eventpoll: prefer kfree_rcu() in __ep_remove()

In '__ep_remove()', prefer 'kfree_rcu()' over 'call_rcu()' with
dummy 'epi_rcu_free()' callback. This follows commit d0089603fa7a
("fs: prefer kfree_rcu() in fasync_remove_entry()") and should not
be backported to stable as well.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Link: https://lore.kernel.org/r/20240221112205.48389-2-dmantipov@yandex.ru
Signed-off-by: Christian Brauner <brauner@kernel.org>

eventpoll: Add epoll ioctl for epoll_params

Add an ioctl for getting and setting epoll_params. User programs can use
this ioctl to get and set the busy poll usec time, packet budget, and
prefer busy poll params for a specific epoll context.

Parameters are limited:
- busy_poll_usecs is limited to <= s32_max
- busy_poll_budget is limited to <= NAPI_POLL_WEIGHT by unprivileged
users (!capable(CAP_NET_ADMIN))
- prefer_busy_poll must be 0 or 1
- __pad must be 0

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

eventpoll: Add per-epoll prefer busy poll option

When using epoll-based busy poll, the prefer_busy_poll option is hardcoded
to false. Users may want to enable prefer_busy_poll to be used in
conjunction with gro_flush_timeout and defer_hard_irqs_count to keep device
IRQs masked.

Other busy poll methods allow enabling or disabling prefer busy poll via
SO_PREFER_BUSY_POLL, but epoll-based busy polling uses a hardcoded value.

Fix this edge case by adding support for a per-epoll context
prefer_busy_poll option. The default is false, as it was hardcoded before
this change.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

eventpoll: Add per-epoll busy poll packet budget

When using epoll-based busy poll, the packet budget is hardcoded to
BUSY_POLL_BUDGET (8). Users may desire larger busy poll budgets, which
can potentially increase throughput when busy polling under high network
load.

Other busy poll methods allow setting the busy poll budget via
SO_BUSY_POLL_BUDGET, but epoll-based busy polling uses a hardcoded
value.

Fix this edge case by adding support for a per-epoll context busy poll
packet budget. If not specified, the default value (BUSY_POLL_BUDGET) is
used.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

eventpoll: support busy poll per epoll instance

Allow busy polling on a per-epoll context basis. The per-epoll context
usec timeout value is preferred, but the pre-existing system wide sysctl
value is still supported if it specified.

busy_poll_usecs is a u32, but in a follow up patch the ioctl provided to
the user only allows setting a value from 0 to S32_MAX.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

epoll: Remove ep_scan_ready_list() in comments

Since commit 443f1a042233 ("lift the calls of ep_send_events_proc()
into the callers"), ep_scan_ready_list() has been removed.
But there are still several in comments. All of them should
be replaced with other caller functions.

Signed-off-by: Huang Xiaojia <huangxiaojia2@huawei.com>
Link: https://lore.kernel.org/r/20240206014353.4191262-1-huangxiaojia2@huawei.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs: Remove the now superfluous sentinel elements from ctl_table array

This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which
will reduce the overall build time size of the kernel and run time
memory bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)

Remove sentinel elements ctl_table struct. Special attention was placed in
making sure that an empty directory for fs/verity was created when
CONFIG_FS_VERITY_BUILTIN_SIGNATURES is not defined. In this case we use the
register sysctl call that expects a size.

Signed-off-by: Joel Granados <j.granados@samsung.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

treewide: mark stuff as __ro_after_init

__read_mostly predates __ro_after_init. Many variables which are marked
__read_mostly should have been __ro_after_init from day 1.

Also, mark some stuff as "const" and "__init" while I'm at it.

[akpm@linux-foundation.org: revert sysctl_nr_open_min, sysctl_nr_open_max changes due to arm warning]
[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/4f6bb9c0-abba-4ee4-a7aa-89265e886817@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

epoll: simplify ep_alloc()

The get_current_user() does not fail, and moving it after kzalloc() can
simplify the code a bit.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Message-Id: <20230726032135.933-1-thunder.leizhen@huaweicloud.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

epoll: ep_autoremove_wake_function should use list_del_init_careful

autoremove_wake_function uses list_del_init_careful, so should epoll's
more aggressive variant. It only doesn't because it was copied from an
older wait.c rather than the most recent.

[bsegall@google.com: add comment]
Link: https://lkml.kernel.org/r/xm26bki0ulsr.fsf_-_@google.com
Link: https://lkml.kernel.org/r/xm26pm6hvfer.fsf@google.com
Fixes: a16ceb139610 ("epoll: autoremove wakers even more aggressively")
Signed-off-by: Ben Segall <bsegall@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs: use correct __poll_t type

Fix the following sparse warnings by using __poll_t instead
of unsigned type.

fs/eventpoll.c:541:9: sparse: warning: restricted __poll_t degrades to integer
fs/eventfd.c:67:17: sparse: warning: restricted __poll_t degrades to integer

Signed-off-by: Min-Hua Chen <minhuadotchen@gmail.com>
Message-Id: <20230511164628.336586-1-minhuadotchen@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

epoll: rename global epmutex

As of 4f04cbaf128 ("epoll: use refcount to reduce ep_mutex contention"),
this lock is now specific to nesting cases - inserting an epoll fd onto
another epoll fd. Rename the lock to be less generic.

Link: https://lkml.kernel.org/r/20230411234159.20421-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

epoll: use refcount to reduce ep_mutex contention

We are observing huge contention on the epmutex during an http
connection/rate test:

83.17% 0.25% nginx [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe
[...]
|--66.96%--__fput
|--60.04%--eventpoll_release_file
|--58.41%--__mutex_lock.isra.6
|--56.56%--osq_lock

The application is multi-threaded, creates a new epoll entry for
each incoming connection, and does not delete it before the
connection shutdown - that is, before the connection's fd close().

Many different threads compete frequently for the epmutex lock,
affecting the overall performance.

To reduce the contention this patch introduces explicit reference counting
for the eventpoll struct. Each registered event acquires a reference,
and references are released at ep_remove() time.

The eventpoll struct is released by whoever - among EP file close() and
and the monitored file close() drops its last reference.

Additionally, this introduces a new 'dying' flag to prevent races between
the EP file close() and the monitored file close().
ep_eventpoll_release() marks, under f_lock spinlock, each epitem as dying
before removing it, while EP file close() does not touch dying epitems.

The above is needed as both close operations could run concurrently and
drop the EP reference acquired via the epitem entry. Without the above
flag, the monitored file close() could reach the EP struct via the epitem
list while the epitem is still listed and then try to put it after its
disposal.

An alternative could be avoiding touching the references acquired via
the epitems at EP file close() time, but that could leave the EP struct
alive for potentially unlimited time after EP file close(), with nasty
side effects.

With all the above in place, we can drop the epmutex usage at disposal time.

Overall this produces a significant performance improvement in the
mentioned connection/rate scenario: the mutex operations disappear from
the topmost offenders in the perf report, and the measured connections/rate
grows by ~60%.

To make the change more readable this additionally renames ep_free() to
ep_clear_and_put(), and moves the actual memory cleanup in a separate
ep_free() helper.

Link: https://lkml.kernel.org/r/4a57788dcaf28f5eb4f8dfddcc3a8b172a7357bb.1679504153.git.pabeni@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Co-developed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Xiumei Mu <xmu@redhiat.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Carlos Maiolino <cmaiolino@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jacob Keller <jacob.e.keller@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Move ep_take_care_of_epollwakeup() to fs/eventpoll.c

This doesn't make any sense to expose to userspace, so it's been moved
to the one user. This was introduced by commit 95f19f658ce1 ("epoll:
drop EPOLLWAKEUP if PM_SLEEP is disabled").

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Reviewed-by: Andrew Waterman <waterman@eecs.berkeley.edu>
Reviewed-by: Albert Ou <aou@eecs.berkeley.edu>
Message-Id: <1447119071-19392-7-git-send-email-palmer@dabbelt.com>
[thuth: Rebased to fix contextual conflicts]
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

eventpoll: align comment with nested epoll limitation

fix comment in commit 02edc6fc4d5f ("epoll: comment the funky #ifdef")

Signed-off-by: Liu, Changcheng <changchengx.liu@outlook.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

eventpoll: add EPOLL_URING_WAKE poll wakeup flag

We can have dependencies between epoll and io_uring. Consider an epoll
context, identified by the epfd file descriptor, and an io_uring file
descriptor identified by iofd. If we add iofd to the epfd context, and
arm a multishot poll request for epfd with iofd, then the multishot
poll request will repeatedly trigger and generate events until terminated
by CQ ring overflow. This isn't a desired behavior.

Add EPOLL_URING so that io_uring can pass it in as part of the poll wakeup
key, and io_uring can check for that to detect a potential recursive
invocation.

Cc: stable@vger.kernel.org # 6.0
Signed-off-by: Jens Axboe <axboe@kernel.dk>

epoll: use try_cmpxchg in list_add_tail_lockless

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
list_add_tail_lockless. x86 CMPXCHG instruction returns success in ZF
flag, so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

No functional change intended.

Link: https://lkml.kernel.org/r/20220714173255.12987-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

epoll: autoremove wakers even more aggressively

If a process is killed or otherwise exits while having active network
connections and many threads waiting on epoll_wait, the threads will all
be woken immediately, but not removed from ep->wq. Then when network
traffic scans ep->wq in wake_up, every wakeup attempt will fail, and will
not remove the entries from the list.

This means that the cost of the wakeup attempt is far higher than usual,
does not decrease, and this also competes with the dying threads trying to
actually make progress and remove themselves from the wq.

Handle this by removing visited epoll wq entries unconditionally, rather
than only when the wakeup succeeds - the structure of ep_poll means that
the only potential loss is the timed_out->eavail heuristic, which now can
race and result in a redundant ep_send_events attempt. (But only when
incoming data and a timeout actually race, not on every timeout)

Shakeel added:

: We are seeing this issue in production with real workloads and it has
: caused hard lockups. Particularly network heavy workloads with a lot
: of threads in epoll_wait() can easily trigger this issue if they get
: killed (oom-killed in our case).

Link: https://lkml.kernel.org/r/xm26fsjotqda.fsf@google.com
Signed-off-by: Ben Segall <bsegall@google.com>
Tested-by: Shakeel Butt <shakeelb@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Roman Penyaev <rpenyaev@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Khazhismel Kumykov <khazhy@google.com>
Cc: Heiher <r@hev.cc>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

eventpoll: simplify sysctl declaration with register_sysctl()

The kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.

To help with this maintenance let's start by moving sysctls to places
where they actually belong. The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we
just care about the core logic.

So move the epoll_table sysctl to fs/eventpoll.c and use
register_sysctl().

Link: https://lkml.kernel.org/r/20211123202422.819032-9-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: David Airlie <airlied@linux.ie>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Julia Lawall <julia.lawall@inria.fr>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Qing Wang <wangqing@vivo.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ARM: 9108/1: oabi-compat: rework epoll_wait/epoll_pwait emulation

The epoll_wait() system call wrapper is one of the remaining users of
the set_fs() infrasturcture for Arm. Changing it to not require set_fs()
is rather complex unfortunately.

The approach I'm taking here is to allow architectures to override
the code that copies the output to user space, and let the oabi-compat
implementation check whether it is getting called from an EABI or OABI
system call based on the thread_info->syscall value.

The in_oabi_syscall() check here mirrors the in_compat_syscall() and
in_x32_syscall() helpers for 32-bit compat implementations on other
architectures.

Overall, the amount of code goes down, at least with the newly added
sys_oabi_epoll_pwait() helper getting removed again. The downside
is added complexity in the source code for the native implementation.
There should be no difference in runtime performance except for Arm
kernels with CONFIG_OABI_COMPAT enabled that now have to go through
an external function call to check which of the two variants to use.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

fs/epoll: use a per-cpu counter for user's watches count

This counter tracks the number of watches a user has, to compare against
the 'max_user_watches' limit. This causes a scalability bottleneck on
SPECjbb2015 on large systems as there is only one user. Changing to a
per-cpu counter increases throughput of the benchmark by about 30% on a
16-socket, > 1000 thread system.

[rdunlap@infradead.org: fix build errors in kernel/user.c when CONFIG_EPOLL=n]
[npiggin@gmail.com: move ifdefs into wrapper functions, slightly improve panic message]
Link: https://lkml.kernel.org/r/1628051945.fens3r99ox.astroid@bobo.none
[akpm@linux-foundation.org: tweak user_epoll_alloc(), per Guenter]
Link: https://lkml.kernel.org/r/20210804191421.GA1900577@roeck-us.net

Link: https://lkml.kernel.org/r/20210802032013.2751916-1-npiggin@gmail.com
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reported-by: Anton Blanchard <anton@ozlabs.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: restore waking from ep_done_scan()

Commit 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested
epoll") changed the userspace visible behavior of exclusive waiters
blocked on a common epoll descriptor upon a single event becoming ready.

Previously, all tasks doing epoll_wait would awake, and now only one is
awoken, potentially causing missed wakeups on applications that rely on
this behavior, such as Apache Qpid.

While the aforementioned commit aims at having only a wakeup single path
in ep_poll_callback (with the exceptions of epoll_ctl cases), we need to
restore the wakeup in what was the old ep_scan_ready_list() such that
the next thread can be awoken, in a cascading style, after the waker's
corresponding ep_send_events().

Link: https://lkml.kernel.org/r/20210405231025.33829-3-dave@stgolabs.net
Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll")
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Roman Penyaev <rpenyaev@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs: eventpoll: fix comments & kernel-doc notation

Use the documented kernel-doc format for function Return: descriptions.
Begin constant values in kernel-doc comments with '%'.

Remove kernel-doc "/**" from 2 functions that are not documented with
kernel-doc notation.

Fix typos, punctuation, & grammar.

Also fix a few kernel-doc warnings:

../fs/eventpoll.c:1883: warning: Function parameter or member 'ep' not described in 'ep_loop_check_proc'
../fs/eventpoll.c:1883: warning: Excess function parameter 'priv' description in 'ep_loop_check_proc'
../fs/eventpoll.c:1932: warning: Function parameter or member 'ep' not described in 'ep_loop_check'
../fs/eventpoll.c:1932: warning: Excess function parameter 'from' description in 'ep_loop_check'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE

Userspace has discovered the functionality offered by SYS_kcmp and has
started to depend upon it. In particular, Mesa uses SYS_kcmp for
os_same_file_description() in order to identify when two fd (e.g. device
or dmabuf) point to the same struct file. Since they depend on it for
core functionality, lift SYS_kcmp out of the non-default
CONFIG_CHECKPOINT_RESTORE into the selectable syscall category.

Rasmus Villemoes also pointed out that systemd uses SYS_kcmp to
deduplicate the per-service file descriptor store.

Note that some distributions such as Ubuntu are already enabling
CHECKPOINT_RESTORE in their configs and so, by extension, SYS_kcmp.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/3046
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Will Drewry <wad@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: stable@vger.kernel.org
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> # DRM depends on kcmp
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> # systemd uses kcmp
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210205220012.1983-1-chris@chris-wilson.co.uk

epoll: add syscall epoll_pwait2

Add syscall epoll_pwait2, an epoll_wait variant with nsec resolution that
replaces int timeout with struct timespec. It is equivalent otherwise.

int epoll_pwait2(int fd, struct epoll_event *events,
int maxevents,
const struct timespec *timeout,
const sigset_t *sigset);

The underlying hrtimer is already programmed with nsec resolution.
pselect and ppoll also set nsec resolution timeout with timespec.

The sigset_t in epoll_pwait has a compat variant. epoll_pwait2 needs
the same.

For timespec, only support this new interface on 2038 aware platforms
that define __kernel_timespec_t. So no CONFIG_COMPAT_32BIT_TIME.

Link: https://lkml.kernel.org/r/20201121144401.3727659-3-willemdebruijn.kernel@gmail.com
Signed-off-by: Willem de Bruijn <willemb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: convert internal api to timespec64

Patch series "add epoll_pwait2 syscall", v4.

Enable nanosecond timeouts for epoll.

Analogous to pselect and ppoll, introduce an epoll_wait syscall
variant that takes a struct timespec instead of int timeout.

This patch (of 4):

Make epoll more consistent with select/poll: pass along the timeout as
timespec64 pointer.

In anticipation of additional changes affecting all three polling
mechanisms:

- add epoll_pwait2 syscall with timespec semantics,
and share poll_select_set_timeout implementation.
- compute slack before conversion to absolute time,
to save one ktime_get_ts64 call.

Link: https://lkml.kernel.org/r/20201121144401.3727659-1-willemdebruijn.kernel@gmail.com
Link: https://lkml.kernel.org/r/20201121144401.3727659-2-willemdebruijn.kernel@gmail.com
Signed-off-by: Willem de Bruijn <willemb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: eliminate unnecessary lock for zero timeout

We call ep_events_available() under lock when timeout is 0, and then call
it without locks in the loop for the other cases.

Instead, call ep_events_available() without lock for all cases. For
non-zero timeouts, we will recheck after adding the thread to the wait
queue. For zero timeout cases, by definition, user is opportunistically
polling and will have to call epoll_wait again in the future.

Note that this lock was kept in c5a282e9635e9 because the whole loop was
historically under lock.

This patch results in a 1% CPU/RPC reduction in RPC benchmarks.

Link: https://lkml.kernel.org/r/20201106231635.3528496-9-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: replace gotos with a proper loop

The existing loop is pointless, and the labels make it really hard to
follow the structure.

Replace that control structure with a simple loop that returns when there
are new events, there is a signal, or the thread has timed out.

Link: https://lkml.kernel.org/r/20201106231635.3528496-8-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: pull all code between fetch_events and send_event into the loop

This is a no-op change which simplifies the follow up patches.

Link: https://lkml.kernel.org/r/20201106231635.3528496-7-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: simplify and optimize busy loop logic

ep_events_available() is called multiple times around the busy loop logic,
even though the logic is generally not used. ep_reset_busy_poll_napi_id()
is similarly always called, even when busy loop is not used.

Eliminate ep_reset_busy_poll_napi_id() and inline it inside
ep_busy_loop(). Make ep_busy_loop() return whether there are any events
available after the busy loop. This will eliminate unnecessary loads and
branches, and simplifies the loop.

Link: https://lkml.kernel.org/r/20201106231635.3528496-6-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: move eavail next to the list_empty_careful check

This is a no-op change and simply to make the code more coherent.

Link: https://lkml.kernel.org/r/20201106231635.3528496-5-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: pull fatal signal checks into ep_send_events()

To simplify the code, pull in checking the fatal signals into
ep_send_events(). ep_send_events() is called only from ep_poll().

Note that, previously, we were always checking fatal events, but it is
checked only if eavail is true. This should be fine because the goal of
that check is to quickly return from epoll_wait() when there is a pending
fatal signal.

Link: https://lkml.kernel.org/r/20201106231635.3528496-4-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: simplify signal handling

Check signals before locking ep->lock, and immediately return -EINTR if
there is any signal pending.

This saves a few loads, stores, and branches from the hot path and
simplifies the loop structure for follow up patches.

Link: https://lkml.kernel.org/r/20201106231635.3528496-3-soheil.kdev@gmail.com
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Cc: Guantao Liu <guantaol@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: check for events when removing a timed out thread from the wait queue

Patch series "simplify ep_poll".

This patch series is a followup based on the suggestions and feedback by
Linus:
https://lkml.kernel.org/r/CAHk-=wizk=OxUyQPbO8MS41w2Pag1kniUV5WdD5qWL-gq1kjDA@mail.gmail.com

The first patch in the series is a fix for the epoll race in presence of
timeouts, so that it can be cleanly backported to all affected stable
kernels.

The rest of the patch series simplify the ep_poll() implementation. Some
of these simplifications result in minor performance enhancements as well.
We have kept these changes under self tests and internal benchmarks for a
few days, and there are minor (1-2%) performance enhancements as a result.

This patch (of 8):

After abc610e01c66 ("fs/epoll: avoid barrier after an epoll_wait(2)
timeout"), we break out of the ep_poll loop upon timeout, without checking
whether there is any new events available. Prior to that patch-series we
always called ep_events_available() after exiting the loop.

This can cause races and missed wakeups. For example, consider the
following scenario reported by Guantao Liu:

Suppose we have an eventfd added using EPOLLET to an epollfd.

Thread 1: Sleeps for just below 5ms and then writes to an eventfd.
Thread 2: Calls epoll_wait with a timeout of 5 ms. If it sees an
event of the eventfd, it will write back on that fd.
Thread 3: Calls epoll_wait with a negative timeout.

Prior to abc610e01c66, it is guaranteed that Thread 3 will wake up either
by Thread 1 or Thread 2. After abc610e01c66, Thread 3 can be blocked
indefinitely if Thread 2 sees a timeout right before the write to the
eventfd by Thread 1. Thread 2 will be woken up from
schedule_hrtimeout_range and, with evail 0, it will not call
ep_send_events().

To fix this issue:
1) Simplify the timed_out case as suggested by Linus.
2) while holding the lock, recheck whether the thread was woken up
after its time out has reached.

Note that (2) is different from Linus' original suggestion: It do not set
"eavail = ep_events_available(ep)" to avoid unnecessary contention (when
there are too many timed-out threads and a small number of events), as
well as races mentioned in the discussion thread.

This is the first patch in the series so that the backport to stable
releases is straightforward.

Link: https://lkml.kernel.org/r/20201106231635.3528496-1-soheil.kdev@gmail.com
Link: https://lkml.kernel.org/r/CAHk-=wizk=OxUyQPbO8MS41w2Pag1kniUV5WdD5qWL-gq1kjDA@mail.gmail.com
Link: https://lkml.kernel.org/r/20201106231635.3528496-2-soheil.kdev@gmail.com
Fixes: abc610e01c66 ("fs/epoll: avoid barrier after an epoll_wait(2) timeout")
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Tested-by: Guantao Liu <guantaol@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Guantao Liu <guantaol@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

net: Remove the err argument from sock_from_file

Currently, the sock_from_file prototype takes an "err" pointer that is
either not set or set to -ENOTSOCK IFF the returned socket is NULL. This
makes the error redundant and it is ignored by a few callers.

This patch simplifies the API by letting callers deduce the error based
on whether the returned socket is NULL or not.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Florent Revest <revest@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/bpf/20201204113609.1850150-1-revest@google.com

net: Add SO_BUSY_POLL_BUDGET socket option

This option lets a user set a per socket NAPI budget for
busy-polling. If the options is not set, it will use the default of 8.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/bpf/20201130185205.196029-3-bjorn.topel@gmail.com

net: Introduce preferred busy-polling

The existing busy-polling mode, enabled by the SO_BUSY_POLL socket
option or system-wide using the /proc/sys/net/core/busy_read knob, is
an opportunistic. That means that if the NAPI context is not
scheduled, it will poll it. If, after busy-polling, the budget is
exceeded the busy-polling logic will schedule the NAPI onto the
regular softirq handling.

One implication of the behavior above is that a busy/heavy loaded NAPI
context will never enter/allow for busy-polling. Some applications
prefer that most NAPI processing would be done by busy-polling.

This series adds a new socket option, SO_PREFER_BUSY_POLL, that works
in concert with the napi_defer_hard_irqs and gro_flush_timeout
knobs. The napi_defer_hard_irqs and gro_flush_timeout knobs were
introduced in commit 6f8b12d661d0 ("net: napi: add hard irqs deferral
feature"), and allows for a user to defer interrupts to be enabled and
instead schedule the NAPI context from a watchdog timer. When a user
enables the SO_PREFER_BUSY_POLL, again with the other knobs enabled,
and the NAPI context is being processed by a softirq, the softirq NAPI
processing will exit early to allow the busy-polling to be performed.

If the application stops performing busy-polling via a system call,
the watchdog timer defined by gro_flush_timeout will timeout, and
regular softirq handling will resume.

In summary; Heavy traffic applications that prefer busy-polling over
softirq processing should use this option.

Example usage:

$ echo 2 | sudo tee /sys/class/net/ens785f1/napi_defer_hard_irqs
$ echo 200000 | sudo tee /sys/class/net/ens785f1/gro_flush_timeout

Note that the timeout should be larger than the userspace processing
window, otherwise the watchdog will timeout and fall back to regular
softirq processing.

Enable the SO_BUSY_POLL/SO_PREFER_BUSY_POLL options on your socket.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/bpf/20201130185205.196029-2-bjorn.topel@gmail.com

epoll: take epitem list out of struct file

Move the head of epitem list out of struct file; for epoll ones it's
moved into struct eventpoll (->refs there), for non-epoll - into
the new object (struct epitem_head). In place of ->f_ep_links we
leave a pointer to the list head (->f_ep).

->f_ep is protected by ->f_lock and it's zeroed as soon as the list
of epitems becomes empty (that can happen only in ep_remove() by
now).

The list of files for reverse path check is *not* going through
struct file now - it's a single-linked list going through epitem_head
instances. It's terminated by ERR_PTR(-1) (== EP_UNACTIVE_POINTER),
so the elements of list can be distinguished by head->next != NULL.

epitem_head instances are allocated at ep_insert() time (by
attach_epitem()) and freed either by ep_remove() (if it empties
the set of epitems *and* epitem_head does not belong to the
reverse path check list) or by clear_tfile_check_list() when
the list is emptied (if the set of epitems is empty by that
point). Allocations are done from a separate slab - minimal kmalloc()
size is too large on some architectures.

As the result, we trim struct file _and_ get rid of the games with
temporary file references.

Locking and barriers are interesting (aren't they always); see unlist_file()
and ep_remove() for details. The non-obvious part is that ep_remove() needs
to decide if it will be the one to free the damn thing *before* actually
storing NULL to head->epitems.first - that's what smp_load_acquire is for
in there. unlist_file() lockless path is safe, since we hit it only if
we observe NULL in head->epitems.first and whoever had done that store is
guaranteed to have observed non-NULL in head->next. IOW, their last access
had been the store of NULL into ->epitems.first and we can safely free
the sucker. OTOH, we are under rcu_read_lock() and both epitem and
epitem->file have their freeing RCU-delayed. So if we see non-NULL
->epitems.first, we can grab ->f_lock (all epitems in there share the
same struct file) and safely recheck the emptiness of ->epitems; again,
->next is still non-NULL, so ep_remove() couldn't have freed head yet.
->f_lock serializes us wrt ep_remove(); the rest is trivial.

Note that once head->epitems becomes NULL, nothing can get inserted into
it - the only remaining reference to head after that point is from the
reverse path check list.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: massage the check list insertion

in the "non-epoll target" cases do it in ep_insert() rather than
in do_epoll_ctl(), so that we do it only with some epitem is already
guaranteed to exist.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

lift rcu_read_lock() into reverse_path_check()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

convert ->f_ep_links/->fllink to hlist

we don't care about the order of elements there

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_insert(): move creation of wakeup source past the fl_ep_links insertion

That's the beginning of preparations for taking f_ep_links out of struct file.
If insertion might fail, we will need a new failure exit. Having wakeup
source creation done after that point will simplify life there; ep_remove()
can (and commonly does) live with NULL epi->ws, so it can be used for
cleanup after ep_create_wakeup_source() failure. It can't be used before
the rbtree insertion, though, so if we are to unify all old failure exits,
we need to move that thing down. Then we would be free to do simple
kmem_cache_free() on the failure to insert into f_ep_links - no wakeup source
to leak on that failure exit.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fold ep_read_events_proc() into the only caller

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

take the common part of ep_eventpoll_poll() and ep_item_poll() into helper

The only reason why ep_item_poll() can't simply call ep_eventpoll_poll()
(or, better yet, call vfs_poll() in all cases) is that we need to tell
lockdep how deep into the hierarchy of ->mtx we are. So let's add
a variant of ep_eventpoll_poll() that would take depth explicitly
and turn ep_eventpoll_poll() into wrapper for that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_insert(): we only need tep->mtx around the insertion itself

We do need ep->mtx (and we are holding it all along), but that's
the lock on the epoll we are inserting into; locking of the
epoll being inserted is not needed for most of that work -
as the matter of fact, we only need it to provide barriers
for the fastpath check (for now).

Move taking and releasing it into ep_insert(). The caller
(do_epoll_ctl()) doesn't need to bother with that at all.
Moreover, that way we kill the kludge in ep_item_poll() - now
it's always called with tep unlocked.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_insert(): don't open-code ep_remove() on failure exits

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

lift locking/unlocking ep->mtx out of ep_{start,done}_scan()

get rid of depth/ep_locked arguments there and document
the kludge in ep_item_poll() that has lead to ep_locked existence in
the first place

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_send_events_proc(): fold into the caller

... and get rid of struct ep_send_events_data - not needed anymore.
The weird way of passing the arguments in (and real return value
out - nominal return value of ep_send_events_proc() is ignored)
was due to the signature forced on ep_scan_ready_list() callbacks.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

lift the calls of ep_send_events_proc() into the callers

... and kill ep_scan_ready_list()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

lift the calls of ep_read_events_proc() into the callers

Expand the calls of ep_scan_ready_list() that get ep_read_events_proc().
As a side benefit we can pass depth to ep_read_events_proc() by value
and not by address - the latter used to be forced by the signature
expected from ep_scan_ready_list() callback.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_scan_ready_list(): prepare to splitup

take the stuff done before and after the callback into separate helpers

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_loop_check_proc(): saner calling conventions

1) 'cookie' argument is unused; kill it.
2) 'priv' one is always an epoll struct file, and we only care
about its associated struct eventpoll; pass that instead.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

get rid of ep_push_nested()

The only remaining user is loop checking. But there we only need
to check that we have not walked into the epoll we are inserting
into - we are adding an edge to acyclic graph, so any loop being
created will have to pass through the source of that edge.

So we don't need that array of cookies - we have only one eventpoll
to watch out for. RIP ep_push_nested(), along with the cookies
array.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_loop_check_proc(): lift pushing the cookie into callers

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

clean reverse_path_check_proc() a bit

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

reverse_path_check_proc(): don't bother with cookies

We know there's no loops by the time we call it; the
only thing we care about is too deep reverse paths.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

reverse_path_check_proc(): sane arguments

no need to force its calling conventions to match the callback for
late unlamented ep_call_nested()...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

untangling ep_call_nested(): and there was much rejoicing

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

untangling ep_call_nested(): move push/pop of cookie into the callbacks

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

untangling ep_call_nested(): take pushing cookie into a helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

untangling ep_call_nested(): it's all serialized on epmutex.

IOW,
* no locking is needed to protect the list
* the list is actually a stack
* no need to check ->ctx
* it can bloody well be a static 5-element array - nobody is
going to be accessing it in parallel.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

untangling ep_call_nested(): get rid of useless arguments

ctx is always equal to current, ncalls - to &poll_loop_ncalls.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: get rid of epitem->nwait

we use it only to indicate allocation failures within queueing
callback back to ep_insert(). Might as well use epq.epi for that
reporting...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: switch epitem->pwqlist to single-linked list

We only traverse it once to destroy all associated eppoll_entry at
epitem destruction time. The order of traversal is irrelevant there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_create_wakeup_source(): dentry name can change under you...

or get freed, for that matter, if it's a long (separately stored)
name.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: EPOLL_CTL_ADD: close the race in decision to take fast path

Checking for the lack of epitems refering to the epoll we want to insert into
is not enough; we might have an insertion of that epoll into another one that
has already collected the set of files to recheck for excessive reverse paths,
but hasn't gotten to creating/inserting the epitem for it.

However, any such insertion in progress can be detected - it will update the
generation count in our epoll when it's done looking through it for files
to check. That gets done under ->mtx of our epoll and that allows us to
detect that safely.

We are *not* holding epmutex here, so the generation count is not stable.
However, since both the update of ep->gen by loop check and (later)
insertion into ->f_ep_link are done with ep->mtx held, we are fine -
the sequence is
grab epmutex
bump loop_check_gen
...
grab tep->mtx // 1
tep->gen = loop_check_gen
...
drop tep->mtx // 2
...
grab tep->mtx // 3
...
insert into ->f_ep_link
...
drop tep->mtx // 4
bump loop_check_gen
drop epmutex
and if the fastpath check in another thread happens for that
eventpoll, it can come
* before (1) - in that case fastpath is just fine
* after (4) - we'll see non-empty ->f_ep_link, slow path
taken
* between (2) and (3) - loop_check_gen is stable,
with ->mtx providing barriers and we end up taking slow path.

Note that ->f_ep_link emptiness check is slightly racy - we are protected
against insertions into that list, but removals can happen right under us.
Not a problem - in the worst case we'll end up taking a slow path for
no good reason.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: replace ->visited/visited_list with generation count

removes the need to clear it, along with the races.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: do not insert into poll queues until all sanity checks are done

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fix regression in "epoll: Keep a reference on files added to the check list"

epoll_loop_check_proc() can run into a file already committed to destruction;
we can't grab a reference on those and don't need to add them to the set for
reverse path check anyway.

Tested-by: Marc Zyngier <maz@kernel.org>
Fixes: a9ed4a6560b8 ("epoll: Keep a reference on files added to the check list")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

do_epoll_ctl(): clean the failure exits up a bit

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: Keep a reference on files added to the check list

When adding a new fd to an epoll, and that this new fd is an
epoll fd itself, we recursively scan the fds attached to it
to detect cycles, and add non-epool files to a "check list"
that gets subsequently parsed.

However, this check list isn't completely safe when deletions
can happen concurrently. To sidestep the issue, make sure that
a struct file placed on the check list sees its f_count increased,
ensuring that a concurrent deletion won't result in the file
disapearing from under our feet.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: call final ep_events_available() check under the lock

There is a possible race when ep_scan_ready_list() leaves ->rdllist and
->obflist empty for a short period of time although some events are
pending. It is quite likely that ep_events_available() observes empty
lists and goes to sleep.

Since commit 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of
nested epoll") we are conservative in wakeups (there is only one place
for wakeup and this is ep_poll_callback()), thus ep_events_available()
must always observe correct state of two lists.

The easiest and correct way is to do the final check under the lock.
This does not impact the performance, since lock is taken anyway for
adding a wait entry to the wait queue.

The discussion of the problem can be found here:

https://lore.kernel.org/linux-fsdevel/a2f22c3c-c25a-4bda-8339-a7bdaf17849e@akamai.com/

In this patch barrierless __set_current_state() is used. This is safe
since waitqueue_active() is called under the same lock on wakeup side.

Short-circuit for fatal signals (i.e. fatal_signal_pending() check) is
moved to the line just before actual events harvesting routine. This is
fully compliant to what is said in the comment of the patch where the
actual fatal_signal_pending() check was added: c257a340ede0 ("fs, epoll:
short circuit fetching events if thread has been killed").

Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll")
Reported-by: Jason Baron <jbaron@akamai.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jason Baron <jbaron@akamai.com>
Cc: Khazhismel Kumykov <khazhy@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200505145609.1865152-1-rpenyaev@suse.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: atomically remove wait entry on wake up

This patch does two things:

- fixes a lost wakeup introduced by commit 339ddb53d373 ("fs/epoll:
remove unnecessary wakeups of nested epoll")

- improves performance for events delivery.

The description of the problem is the following: if N (>1) threads are
waiting on ep->wq for new events and M (>1) events come, it is quite
likely that >1 wakeups hit the same wait queue entry, because there is
quite a big window between __add_wait_queue_exclusive() and the
following __remove_wait_queue() calls in ep_poll() function.

This can lead to lost wakeups, because thread, which was woken up, can
handle not all the events in ->rdllist. (in better words the problem is
described here: https://lkml.org/lkml/2019/10/7/905)

The idea of the current patch is to use init_wait() instead of
init_waitqueue_entry().

Internally init_wait() sets autoremove_wake_function as a callback,
which removes the wait entry atomically (under the wq locks) from the
list, thus the next coming wakeup hits the next wait entry in the wait
queue, thus preventing lost wakeups.

Problem is very well reproduced by the epoll60 test case [1].

Wait entry removal on wakeup has also performance benefits, because
there is no need to take a ep->lock and remove wait entry from the queue
after the successful wakeup. Here is the timing output of the epoll60
test case:

With explicit wakeup from ep_scan_ready_list() (the state of the
code prior 339ddb53d373):

real 0m6.970s
user 0m49.786s
sys 0m0.113s

After this patch:

real 0m5.220s
user 0m36.879s
sys 0m0.019s

The other testcase is the stress-epoll [2], where one thread consumes
all the events and other threads produce many events:

With explicit wakeup from ep_scan_ready_list() (the state of the
code prior 339ddb53d373):

threads events/ms run-time ms
8 5427 1474
16 6163 2596
32 6824 4689
64 7060 9064
128 6991 18309

After this patch:

threads events/ms run-time ms
8 5598 1429
16 7073 2262
32 7502 4265
64 7640 8376
128 7634 16767

(number of "events/ms" represents event bandwidth, thus higher is
better; number of "run-time ms" represents overall time spent
doing the benchmark, thus lower is better)

[1] tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
[2] https://github.com/rouming/test-tools/blob/master/stress-epoll.c

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jason Baron <jbaron@akamai.com>
Cc: Khazhismel Kumykov <khazhy@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Heiher <r@hev.cc>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200430130326.1368509-2-rpenyaev@suse.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

eventpoll: fix missing wakeup for ovflist in ep_poll_callback

In the event that we add to ovflist, before commit 339ddb53d373
("fs/epoll: remove unnecessary wakeups of nested epoll") we would be
woken up by ep_scan_ready_list, and did no wakeup in ep_poll_callback.

With that wakeup removed, if we add to ovflist here, we may never wake
up. Rather than adding back the ep_scan_ready_list wakeup - which was
resulting in unnecessary wakeups, trigger a wake-up in ep_poll_callback.

We noticed that one of our workloads was missing wakeups starting with
339ddb53d373 and upon manual inspection, this wakeup seemed missing to me.
With this patch added, we no longer see missing wakeups. I haven't yet
tried to make a small reproducer, but the existing kselftests in
filesystem/epoll passed for me with this patch.

[khazhy@google.com: use if/elif instead of goto + cleanup suggested by Roman]
Link: http://lkml.kernel.org/r/20200424190039.192373-1-khazhy@google.com
Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll")
Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Roman Penyaev <rpenyaev@suse.de>
Cc: Heiher <r@hev.cc>
Cc: Jason Baron <jbaron@akamai.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200424025057.118641-1-khazhy@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: make nesting accounting safe for -rt kernel

Davidlohr Bueso pointed out that when CONFIG_DEBUG_LOCK_ALLOC is set
ep_poll_safewake() can take several non-raw spinlocks after disabling
interrupts. Since a spinlock can block in the -rt kernel, we can't take a
spinlock after disabling interrupts. So let's re-work how we determine
the nesting level such that it plays nicely with the -rt kernel.

Let's introduce a 'nests' field in struct eventpoll that records the
current nesting level during ep_poll_callback(). Then, if we nest again
we can find the previous struct eventpoll that we were called from and
increase our count by 1. The 'nests' field is protected by
ep->poll_wait.lock.

I've also moved the visited field to reduce the size of struct eventpoll
from 184 bytes to 176 bytes on x86_64 for !CONFIG_DEBUG_LOCK_ALLOC, which
is typical for a production config.

Reported-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Roman Penyaev <rpenyaev@suse.de>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: http://lkml.kernel.org/r/1582739816-13167-1-git-send-email-jbaron@akamai.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix possible lost wakeup on epoll_ctl() path

This fixes possible lost wakeup introduced by commit a218cc491420.
Originally modifications to ep->wq were serialized by ep->wq.lock, but
in commit a218cc491420 ("epoll: use rwlock in order to reduce
ep_poll_callback() contention") a new rw lock was introduced in order to
relax fd event path, i.e. callers of ep_poll_callback() function.

After the change ep_modify and ep_insert (both are called on epoll_ctl()
path) were switched to ep->lock, but ep_poll (epoll_wait) was using
ep->wq.lock on wqueue list modification.

The bug doesn't lead to any wqueue list corruptions, because wake up
path and list modifications were serialized by ep->wq.lock internally,
but actual waitqueue_active() check prior wake_up() call can be
reordered with modifications of ep ready list, thus wake up can be lost.

And yes, can be healed by explicit smp_mb():

list_add_tail(&epi->rdlink, &ep->rdllist);
smp_mb();
if (waitqueue_active(&ep->wq))
wake_up(&ep->wp);

But let's make it simple, thus current patch replaces ep->wq.lock with
the ep->lock for wqueue modifications, thus wake up path always observes
activeness of the wqueue correcty.

Fixes: a218cc491420 ("epoll: use rwlock in order to reduce ep_poll_callback() contention")
Reported-by: Max Neunhoeffer <max@arangodb.com>
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Max Neunhoeffer <max@arangodb.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Christopher Kohlhoff <chris.kohlhoff@clearpool.io>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Jes Sorensen <jes.sorensen@gmail.com>
Cc: <stable@vger.kernel.org> [5.1+]
Link: http://lkml.kernel.org/r/20200214170211.561524-1-rpenyaev@suse.de
References: https://bugzilla.kernel.org/show_bug.cgi?id=205933
Bisected-by: Max Neunhoeffer <max@arangodb.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

eventpoll: support non-blocking do_epoll_ctl() calls

Also make it available outside of epoll, along with the helper that
decides if we need to copy the passed in epoll_event.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

eventpoll: abstract out epoll_ctl() handler

No functional changes in this patch.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/epoll: remove unnecessary wakeups of nested epoll

Take the case where we have:

t0
| (ew)
e0
| (et)
e1
| (lt)
s0

t0: thread 0
e0: epoll fd 0
e1: epoll fd 1
s0: socket fd 0
ew: epoll_wait
et: edge-trigger
lt: level-trigger

We remove unnecessary wakeups to prevent the nested epoll that working in edge-
triggered mode to waking up continuously.

Test code:
#include <unistd.h>
#include <sys/epoll.h>
#include <sys/socket.h>

int main(int argc, char *argv[])
{
int sfd[2];
int efd[2];
struct epoll_event e;

if (socketpair(AF_UNIX, SOCK_STREAM, 0, sfd) < 0)
goto out;

efd[0] = epoll_create(1);
if (efd[0] < 0)
goto out;

efd[1] = epoll_create(1);
if (efd[1] < 0)
goto out;

e.events = EPOLLIN;
if (epoll_ctl(efd[1], EPOLL_CTL_ADD, sfd[0], &e) < 0)
goto out;

e.events = EPOLLIN | EPOLLET;
if (epoll_ctl(efd[0], EPOLL_CTL_ADD, efd[1], &e) < 0)
goto out;

if (write(sfd[1], "w", 1) != 1)
goto out;

if (epoll_wait(efd[0], &e, 1, 0) != 1)
goto out;

if (epoll_wait(efd[0], &e, 1, 0) != 0)
goto out;

close(efd[0]);
close(efd[1]);
close(sfd[0]);
close(sfd[1]);

return 0;

out:
return -1;
}

More tests:
https://github.com/heiher/epoll-wakeup

Link: http://lkml.kernel.org/r/20191009060516.3577-1-r@hev.cc
Signed-off-by: hev <r@hev.cc>
Reviewed-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Eric Wong <e@80x24.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: simplify ep_poll_safewake() for CONFIG_DEBUG_LOCK_ALLOC

Currently, ep_poll_safewake() in the CONFIG_DEBUG_LOCK_ALLOC case uses
ep_call_nested() in order to pass the correct subclass argument to
spin_lock_irqsave_nested(). However, ep_call_nested() adds unnecessary
checks for epoll depth and loops that are already verified when doing
EPOLL_CTL_ADD. This mirrors a conversion that was done for
!CONFIG_DEBUG_LOCK_ALLOC in: commit 37b5e5212a44 ("epoll: remove
ep_call_nested() from ep_eventpoll_poll()")

Link: http://lkml.kernel.org/r/1567628549-11501-1-git-send-email-jbaron@akamai.com
Signed-off-by: Jason Baron <jbaron@akamai.com>
Reviewed-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

PM / wakeup: Show wakeup sources stats in sysfs

Add an ID and a device pointer to 'struct wakeup_source'. Use them to to
expose wakeup sources statistics in sysfs under
/sys/class/wakeup/wakeup<ID>/*.

Co-developed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Tri Vo <trong@android.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

proc/sysctl: add shared variables for range check

In the sysctl code the proc_dointvec_minmax() function is often used to
validate the user supplied value between an allowed range. This
function uses the extra1 and extra2 members from struct ctl_table as
minimum and maximum allowed value.

On sysctl handler declaration, in every source file there are some
readonly variables containing just an integer which address is assigned
to the extra1 and extra2 members, so the sysctl range is enforced.

The special values 0, 1 and INT_MAX are very often used as range
boundary, leading duplication of variables like zero=0, one=1,
int_max=INT_MAX in different source files:

$ git grep -E '\.extra[12].*&(zero|one|int_max)' |wc -l
248

Add a const int array containing the most commonly used values, some
macros to refer more easily to the correct array member, and use them
instead of creating a local one for every object file.

This is the bloat-o-meter output comparing the old and new binary
compiled with the default Fedora config:

# scripts/bloat-o-meter -d vmlinux.o.old vmlinux.o
add/remove: 2/2 grow/shrink: 0/2 up/down: 24/-188 (-164)
Data old new delta
sysctl_vals - 12 +12
__kstrtab_sysctl_vals - 12 +12
max 14 10 -4
int_max 16 - -16
one 68 - -68
zero 128 28 -100
Total: Before=20583249, After=20583085, chg -0.00%

[mcroce@redhat.com: tipc: remove two unused variables]
Link: http://lkml.kernel.org/r/20190530091952.4108-1-mcroce@redhat.com
[akpm@linux-foundation.org: fix net/ipv6/sysctl_net_ipv6.c]
[arnd@arndb.de: proc/sysctl: make firmware loader table conditional]
Link: http://lkml.kernel.org/r/20190617130014.1713870-1-arnd@arndb.de
[akpm@linux-foundation.org: fix fs/eventpoll.c]
Link: http://lkml.kernel.org/r/20190430180111.10688-1-mcroce@redhat.com
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

signal: simplify set_user_sigmask/restore_user_sigmask

task->saved_sigmask and ->restore_sigmask are only used in the ret-from-
syscall paths. This means that set_user_sigmask() can save ->blocked in
->saved_sigmask and do set_restore_sigmask() to indicate that ->blocked
was modified.

This way the callers do not need 2 sigset_t's passed to set/restore and
restore_user_sigmask() renamed to restore_saved_sigmask_unless() turns
into the trivial helper which just calls restore_saved_sigmask().

Link: http://lkml.kernel.org/r/20190606113206.GA9464@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Eric Wong <e@80x24.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: David Laight <David.Laight@aculab.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

signal: remove the wrong signal_pending() check in restore_user_sigmask()

This is the minimal fix for stable, I'll send cleanups later.

Commit 854a6ed56839 ("signal: Add restore_user_sigmask()") introduced
the visible change which breaks user-space: a signal temporary unblocked
by set_user_sigmask() can be delivered even if the caller returns
success or timeout.

Change restore_user_sigmask() to accept the additional "interrupted"
argument which should be used instead of signal_pending() check, and
update the callers.

Eric said:

: For clarity. I don't think this is required by posix, or fundamentally to
: remove the races in select. It is what linux has always done and we have
: applications who care so I agree this fix is needed.
:
: Further in any case where the semantic change that this patch rolls back
: (aka where allowing a signal to be delivered and the select like call to
: complete) would be advantage we can do as well if not better by using
: signalfd.
:
: Michael is there any chance we can get this guarantee of the linux
: implementation of pselect and friends clearly documented. The guarantee
: that if the system call completes successfully we are guaranteed that no
: signal that is unblocked by using sigmask will be delivered?

Link: http://lkml.kernel.org/r/20190604134117.GA29963@redhat.com
Fixes: 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add restore_user_sigmask()")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Eric Wong <e@80x24.org>
Tested-by: Eric Wong <e@80x24.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: <stable@vger.kernel.org> [5.0+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

epoll: use rwlock in order to reduce ep_poll_callback() contention

The goal of this patch is to reduce contention of ep_poll_callback()
which can be called concurrently from different CPUs in case of high
events rates and many fds per epoll. Problem can be very well
reproduced by generating events (write to pipe or eventfd) from many
threads, while consumer thread does polling. In other words this patch
increases the bandwidth of events which can be delivered from sources to
the poller by adding poll items in a lockless way to the list.

The main change is in replacement of the spinlock with a rwlock, which
is taken on read in ep_poll_callback(), and then by adding poll items to
the tail of the list using xchg atomic instruction. Write lock is taken
everywhere else in order to stop list modifications and guarantee that
list updates are fully completed (I assume that write side of a rwlock
does not starve, it seems qrwlock implementation has these guarantees).

The following are some microbenchmark results based on the test [1]
which starts threads which generate N events each. The test ends when
all events are successfully fetched by the poller thread:

spinlock
========

threads events/ms run-time ms
8 6402 12495
16 7045 22709
32 7395 43268

rwlock + xchg
=============

threads events/ms run-time ms
8 10038 7969
16 12178 13138
32 13223 24199

According to the results bandwidth of delivered events is significantly
increased, thus execution time is reduced.

This patch was tested with different sort of microbenchmarks and
artificial delays (e.g. "udelay(get_random_int() & 0xff)") introduced
in kernel on paths where items are added to lists.

[1] https://github.com/rouming/test-tools/blob/master/stress-epoll.c

Link: http://lkml.kernel.org/r/20190103150104.17128-5-rpenyaev@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: unify awaking of wakeup source on ep_poll_callback() path

Original comment "Activate ep->ws since epi->ws may get deactivated at
any time" indeed sounds loud, but it is incorrect, because the path
where we check epi->ws is a path where insert to ovflist happens, i.e.
ep_scan_ready_list() has taken ep->mtx and waits for this callback to
finish, thus ep_modify() (which unregisters wakeup source) waits for
ep_scan_ready_list().

Here in this patch I simply call ep_pm_stay_awake_rcu(), which is a bit
extra for this path (indirectly protected by main ep->mtx, so even rcu
is not needed), but I do not want to create another naked
__ep_pm_stay_awake() variant only for this particular case, so rcu variant
is just better for all the cases.

Link: http://lkml.kernel.org/r/20190103150104.17128-4-rpenyaev@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: make sure all elements in ready list are in FIFO order

Patch series "use rwlock in order to reduce ep_poll_callback()
contention", v3.

The last patch targets the contention problem in ep_poll_callback(),
which can be very well reproduced by generating events (write to pipe or
eventfd) from many threads, while consumer thread does polling.

The following are some microbenchmark results based on the test [1]
which starts threads which generate N events each. The test ends when
all events are successfully fetched by the poller thread:

spinlock
========

threads events/ms run-time ms
8 6402 12495
16 7045 22709
32 7395 43268

rwlock + xchg
=============

threads events/ms run-time ms
8 10038 7969
16 12178 13138
32 13223 24199

According to the results bandwidth of delivered events is significantly
increased, thus execution time is reduced.

This patch (of 4):

All coming events are stored in FIFO order and this is also should be
applicable to ->ovflist, which originally is stack, i.e. LIFO.

Thus to keep correct FIFO order ->ovflist should reversed by adding
elements to the head of the read list but not to the tail.

Link: http://lkml.kernel.org/r/20190103150104.17128-2-rpenyaev@suse.de
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: deal with wait_queue only once

There is no reason why we rearm the waitiqueue upon every fetch_events
retry (for when events are found yet send_events() fails). If nothing
else, this saves four lock operations per retry, and furthermore reduces
the scope of the lock even further.

[akpm@linux-foundation.org: restore code to original position, fix and reflow comment]
Link: http://lkml.kernel.org/r/20181114182532.27981-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: rename check_events label to send_events

It is currently called check_events because it, well, did exactly that.
However, since the lockless ep_events_available() call, the label no
longer checks, but just sends the events. Rename as such.

Link: http://lkml.kernel.org/r/20181114182532.27981-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: avoid barrier after an epoll_wait(2) timeout

Upon timeout, we can just exit out of the loop, without the cost of the
changing the task's state with an smp_store_mb call. Just exit out of
the loop and be done - setting the task state afterwards will be, of
course, redundant.

[dave@stgolabs.net: forgotten fixlets]
Link: http://lkml.kernel.org/r/20181109155258.jxcr4t2pnz6zqct3@linux-r8p5
Link: http://lkml.kernel.org/r/20181108051006.18751-7-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: reduce the scope of wq lock in epoll_wait()

This patch aims at reducing ep wq.lock hold times in epoll_wait(2). For
the blocking case, there is no need to constantly take and drop the
spinlock, which is only needed to manipulate the waitqueue.

The call to ep_events_available() is now lockless, and only exposed to
benign races. Here, if false positive (returns available events and
does not see another thread deleting an epi from the list) we call into
send_events and then the list's state is correctly seen. Otoh, if a
false negative and we don't see a list_add_tail(), for example, from irq
callback, then it is rechecked again before blocking, which will see the
correct state.

In order for more accuracy to see concurrent list_del_init(), use the
list_empty_careful() variant -- of course, this won't be safe against
insertions from wakeup.

For the overflow list we obviously need to prevent load/store tearing as
we don't want to see partial values while the ready list is disabled.

[dave@stgolabs.net: forgotten fixlets]
Link: http://lkml.kernel.org/r/20181109155258.jxcr4t2pnz6zqct3@linux-r8p5
Link: http://lkml.kernel.org/r/20181108051006.18751-6-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Suggested-by: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: robustify ep->mtx held checks

Insted of just commenting how important it is, lets make it more robust
and add a lockdep_assert_held() call.

Link: http://lkml.kernel.org/r/20181108051006.18751-5-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: drop ovflist branch prediction

The ep->ovflist is a secondary ready-list to temporarily store events
that might occur when doing sproc without holding the ep->wq.lock. This
accounts for every time we check for ready events and also send events
back to userspace; both callbacks, particularly the latter because of
copy_to_user, can account for a non-trivial time.

As such, the unlikely() check to see if the pointer is being used, seems
both misleading and sub-optimal. In fact, we go to an awful lot of
trouble to sync both lists, and populating the ovflist is far from an
uncommon scenario.

For example, profiling a concurrent epoll_wait(2) benchmark, with
CONFIG_PROFILE_ANNOTATED_BRANCHES shows that for a two threads a 33%
incorrect rate was seen; and when incrementally increasing the number of
epoll instances (which is used, for example for multiple queuing load
balancing models), up to a 90% incorrect rate was seen.

Similarly, by deleting the prediction, 3% throughput boost was seen
across incremental threads.

Link: http://lkml.kernel.org/r/20181108051006.18751-4-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: simplify ep_send_events_proc() ready-list loop

The current logic is a bit convoluted. Lets simplify this with a
standard list_for_each_entry_safe() loop instead and just break out
after maxevents is reached.

While at it, remove an unnecessary indentation level in the loop when
there are in fact ready events.

Link: http://lkml.kernel.org/r/20181108051006.18751-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: remove max_nests argument from ep_call_nested()

Patch series "epoll: some miscellaneous optimizations".

The following are some incremental optimizations on some of the epoll
core. Each patch has the details, but together, the series is seen to
shave off measurable cycles on a number of systems and workloads.

For example, on a 40-core IB, a pipetest as well as parallel
epoll_wait() benchmark show around a 20-30% increase in raw operations
per second when the box is fully occupied (incremental thread counts),
and up to 15% performance improvement with lower counts.

Passes ltp epoll related testcases.

This patch(of 6):

All callers pass the EP_MAX_NESTS constant already, so lets simplify
this a tad and get rid of the redundant parameter for nested eventpolls.

Link: http://lkml.kernel.org/r/20181108051006.18751-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Remove 'type' argument from access_ok() function

Nobody has actually used the type (VERIFY_READ vs VERIFY_WRITE) argument
of the user address range verification function since we got rid of the
old racy i386-only code to walk page tables by hand.

It existed because the original 80386 would not honor the write protect
bit when in kernel mode, so you had to do COW by hand before doing any
user access. But we haven't supported that in a long time, and these
days the 'type' argument is a purely historical artifact.

A discussion about extending 'user_access_begin()' to do the range
checking resulted this patch, because there is no way we're going to
move the old VERIFY_xyz interface to that model. And it's best done at
the end of the merge window when I've done most of my merges, so let's
just get this done once and for all.

This patch was mostly done with a sed-script, with manual fix-ups for
the cases that weren't of the trivial 'access_ok(VERIFY_xyz' form.

There were a couple of notable cases:

- csky still had the old "verify_area()" name as an alias.

- the iter_iov code had magical hardcoded knowledge of the actual
values of VERIFY_{READ,WRITE} (not that they mattered, since nothing
really used it)

- microblaze used the type argument for a debug printout

but other than those oddities this should be a total no-op patch.

I tried to fix up all architectures, did fairly extensive grepping for
access_ok() uses, and the changes are trivial, but I may have missed
something. Any missed conversion should be trivially fixable, though.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

signal: Add restore_user_sigmask()

Refactor the logic to restore the sigmask before the syscall
returns into an api.
This is useful for versions of syscalls that pass in the
sigmask and expect the current->sigmask to be changed during
the execution and restored after the execution of the syscall.

With the advent of new y2038 syscalls in the subsequent patches,
we add two more new versions of the syscalls (for pselect, ppoll
and io_pgetevents) in addition to the existing native and compat
versions. Adding such an api reduces the logic that would need to
be replicated otherwise.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

signal: Add set_user_sigmask()

Refactor reading sigset from userspace and updating sigmask
into an api.

This is useful for versions of syscalls that pass in the
sigmask and expect the current->sigmask to be changed during,
and restored after, the execution of the syscall.

With the advent of new y2038 syscalls in the subsequent patches,
we add two more new versions of the syscalls (for pselect, ppoll,
and io_pgetevents) in addition to the existing native and compat
versions. Adding such an api reduces the logic that would need to
be replicated otherwise.

Note that the calls to sigprocmask() ignored the return value
from the api as the function only returns an error on an invalid
first argument that is hardcoded at these call sites.
The updated logic uses set_current_blocked() instead.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

fs/eventpoll.c: simplify ep_is_linked() callers

Instead of having each caller pass the rdllink explicitly, just have
ep_is_linked() pass it while the callers just need the epi pointer. This
helper is all about the rdllink, and this change, furthermore, improves
the function's self documentation.

Link: http://lkml.kernel.org/r/20180727053432.16679-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventpoll.c: loosen irq safety in ep_poll()

Similar to other calls, ep_poll() is not called with interrupts disabled,
and we can therefore avoid the irq save/restore dance and just disable
local irqs. In fact, the call should never be called in irq context at
all, considering that the only path is

epoll_wait(2) -> do_epoll_wait() -> ep_poll().

When running on a 2 socket 40-core (ht) IvyBridge a common pipe based
epoll_wait(2) microbenchmark, the following performance improvements are
seen:

# threads vanilla dirty
1 1805587 2106412
2 1854064 2090762
4 1805484 2017436
8 1751222 1974475
16 1725299 1962104
32 1378463 1571233
64 787368 900784

Which is a pretty constantly near 15%.

Also add a lockdep check such that we detect any mischief before
deadlocking.

Link: http://lkml.kernel.org/r/20180727053432.16679-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventpoll.c: simply CONFIG_NET_RX_BUSY_POLL ifdefery

... 'tis easier on the eye.

[akpm@linux-foundation.org: use inlines rather than macros]
Link: http://lkml.kernel.org/r/20180725185620.11020-1-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

s/epoll: robustify irq safety with lockdep_assert_irqs_enabled()

Sprinkle lockdep_assert_irqs_enabled() checks in the functions that do not
save and restore interrupts when dealing with the ep->wq.lock. These are
ep_scan_ready_list() and those called by epoll_ctl(): ep_insert, ep_modify
and ep_remove.

[akpm@linux-foundation.org: remove too-obvious comments]
Link: http://lkml.kernel.org/r/20180721183127.3busfa335zlcjeox@linux-r8p5
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: loosen irq safety in epoll_insert() and epoll_remove()

Both functions are similar to the context of ep_modify(), called via
epoll_ctl(2). Just like ep_modify(), saving and restoring interrupts is
an overkill in these calls as it will never be called with irqs disabled.
While ep_remove() can be called directly from EPOLL_CTL_DEL, it can also
be called when releasing the file, but this also complies with the above.

Link: http://lkml.kernel.org/r/20180720172956.2883-3-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/epoll: loosen irq safety in ep_scan_ready_list()

Patch series "fs/epoll: loosen irq safety when possible".

Both patches replace saving+restoring interrupts when taking the ep->lock
(now the waitqueue lock), with just disabling local irqs. This shows
immediate performance benefits in patch 1 for an epoll workload running on
Xen. The main concern we need to have with this sort of changes in epoll
is the ep_poll_callback() which is passed to the wait queue wakeup and is
done very often under irq context, this patch does not touch this call.

Patches have been tested pretty heavily with the customer workload,
microbenchmarks, ltp testcases and two high level workloads that use epoll
under the hood: nginx and libevent benchmarks.

This patch (of 2):

Saving and restoring interrupts in ep_scan_ready_list() is an
overkill as it is never called with interrupts disabled. Loosen
this to simply disabling local irqs such that archs where managing
irqs is expensive or virtual environments. This patch yields
some throughput improvements on a workload that is epoll intensive
running on a single Xen DomU.

1 Job 7500 --> 8800 enq/s (+17%)
2 Jobs 14000 --> 15200 enq/s (+8%)
3 Jobs 20500 --> 22300 enq/s (+8%)
4 Jobs 25000 --> 28000 enq/s (+8-12)%

On bare metal:

For a 2-socket 40-core (ht) IvyBridge on a few workloads, unfortunately I
don't have a xen environment and the results for Xen I do have (which
numbers are in patch 1) I don't have the actual workload, so cannot
compare them directly.

1) Different configurations were used for a epoll_wait (pipes io)
microbench (http://linux-scalability.org/epoll/epoll-test.c) and shows
around a 7-10% improvement in overall total number of times the
epoll_wait() loops when using both regular and nested epolls, so very
raw numbers, but measurable nonetheless.

# threads vanilla dirty
1 1677717 1805587
2 1660510 1854064
4 1610184 1805484
8 1577696 1751222
16 1568837 1725299
32 1291532 1378463
64 752584 787368

Note that stddev is pretty small.

2) Another pipe test, which shows no real measurable improvement.
(http://www.xmailserver.org/linux-patches/pipetest.c)

Link: http://lkml.kernel.org/r/20180720172956.2883-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: use the waitqueue lock to protect ep->wq

Patch series "waitqueue lockdep annotation", v3.

This series adds a strategic lockdep_assert_held to __wake_up_common to
ensure callers really do hold the wait_queue_head lock when calling the
unlocked wake_up variants. It turns out epoll did not do this for a
fairly common path (hit all the time by systemd during bootup), so the
second patch fixed this instance as well.

This patch (of 3):

The epoll code currently uses the unlocked waitqueue helpers for managing
ep->wq, but instead of holding the waitqueue lock around these calls, it
uses its own ep->lock spinlock. Given that the waitqueue is not exposed
to the rest of the kernel this actually works ok at the moment, but
prevents the epoll locking rules from being enforced using lockdep.
Remove ep->lock and use the waitqueue lock to not only reduce the size of
struct eventpoll but also to make sure we can assert locking invariants in
the waitqueue code.

Link: http://lkml.kernel.org/r/20171214152344.6880-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Baron <jbaron@akamai.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL

The poll() changes were not well thought out, and completely
unexplained. They also caused a huge performance regression, because
"->poll()" was no longer a trivial file operation that just called down
to the underlying file operations, but instead did at least two indirect
calls.

Indirect calls are sadly slow now with the Spectre mitigation, but the
performance problem could at least be largely mitigated by changing the
"->get_poll_head()" operation to just have a per-file-descriptor pointer
to the poll head instead. That gets rid of one of the new indirections.

But that doesn't fix the new complexity that is completely unwarranted
for the regular case. The (undocumented) reason for the poll() changes
was some alleged AIO poll race fixing, but we don't make the common case
slower and more complex for some uncommon special case, so this all
really needs way more explanations and most likely a fundamental
redesign.

[ This revert is a revert of about 30 different commits, not reverted
individually because that would just be unnecessarily messy - Linus ]

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

eventpoll: switch to ->poll_mask

Signed-off-by: Ben Noordhuis <info@bnoordhuis.nl>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs: add new vfs_poll and file_can_poll helpers

These abstract out calls to the poll method in preparation for changes
in how we poll.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

fs: add do_epoll_*() helpers; remove internal calls to sys_epoll_*()

Using the helper functions do_epoll_create() and do_epoll_wait() allows us
to remove in-kernel calls to the related syscall functions.

This patch is part of a series which removes in-kernel calls to syscalls.
On this basis, the syscall entry path can be streamlined. For details, see
http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>

vfs: do bulk POLL* -> EPOLL* replacement

This is the mindless scripted replacement of kernel use of POLL*
variables as described by Al, done by this script:

for V in IN OUT PRI ERR RDNORM RDBAND WRNORM WRBAND HUP RDHUP NVAL MSG; do
L=`git grep -l -w POLL$V | grep -v '^t' | grep -v /um/ | grep -v '^sa' | grep -v '/poll.h$'|grep -v '^D'`
for f in $L; do sed -i "-es/^\([^\"]*\)\(\<POLL$V\>\)/\\1E\\2/" $f; done
done

with de-mangling cleanups yet to come.

NOTE! On almost all architectures, the EPOLL* constants have the same
values as the POLL* constants do. But they keyword here is "almost".
For various bad reasons they aren't the same, and epoll() doesn't
actually work quite correctly in some cases due to this on Sparc et al.

The next patch from Al will sort out the final differences, and we
should be all done.

Scripted-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

annotate ep_scan_ready_list()

make it always return __poll_t and have its callbacks do the same

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

ep_send_events_proc(): return result via esed->res

preparations for not mixing __poll_t and int in ep_scan_ready_list()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

eventpoll: no need to mask the result of epi_item_poll() again

two callers that do so don't need to bother - we'd already
masked it with epi->event.events, which
* couldn't have changed since we are holding ->mtx
* had been set to event->events
* is still equal to event->events, since *event is never
changed by anything.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

eventpoll: constify struct epoll_event pointers

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs: annotate ->poll() instances

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

annotate poll-related wait keys

__poll_t is also used as wait key in some waitqueues.
Verify that wait_..._poll() gets __poll_t as key and
provide a helper for wakeup functions to get back to
that __poll_t value.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: remove ep_call_nested() from ep_eventpoll_poll()

The use of ep_call_nested() in ep_eventpoll_poll(), which is the .poll
routine for an epoll fd, is used to prevent excessively deep epoll
nesting, and to prevent circular paths.

However, we are already preventing these conditions during
EPOLL_CTL_ADD. In terms of too deep epoll chains, we do in fact allow
deep nesting of the epoll fds themselves (deeper than EP_MAX_NESTS),
however we don't allow more than EP_MAX_NESTS when an epoll file
descriptor is actually connected to a wakeup source. Thus, we do not
require the use of ep_call_nested(), since ep_eventpoll_poll(), which is
called via ep_scan_ready_list() only continues nesting if there are
events available.

Since ep_call_nested() is implemented using a global lock, applications
that make use of nested epoll can see large performance improvements
with this change.

Davidlohr said:

: Improvements are quite obscene actually, such as for the following
: epoll_wait() benchmark with 2 level nesting on a 80 core IvyBridge:
:
: ncpus vanilla dirty delta
: 1 2447092 3028315 +23.75%
: 4 231265 2986954 +1191.57%
: 8 121631 2898796 +2283.27%
: 16 59749 2902056 +4757.07%
: 32 26837 2326314 +8568.30%
: 64 12926 1341281 +10276.61%
:
: (http://linux-scalability.org/epoll/epoll-test.c)

Link: http://lkml.kernel.org/r/1509430214-5599-1-git-send-email-jbaron@akamai.com
Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Salman Qazi <sqazi@google.com>
Cc: Hou Tao <houtao1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: avoid calling ep_call_nested() from ep_poll_safewake()

ep_poll_safewake() is used to wakeup potentially nested epoll file
descriptors. The function uses ep_call_nested() to prevent entering the
same wake up queue more than once, and to prevent excessively deep
wakeup paths (deeper than EP_MAX_NESTS). However, this is not necessary
since we are already preventing these conditions during EPOLL_CTL_ADD.
This saves extra function calls, and avoids taking a global lock during
the ep_call_nested() calls.

I have, however, left ep_call_nested() for the CONFIG_DEBUG_LOCK_ALLOC
case, since ep_call_nested() keeps track of the nesting level, and this
is required by the call to spin_lock_irqsave_nested(). It would be nice
to remove the ep_call_nested() calls for the CONFIG_DEBUG_LOCK_ALLOC
case as well, however its not clear how to simply pass the nesting level
through multiple wake_up() levels without more surgery. In any case, I
don't think CONFIG_DEBUG_LOCK_ALLOC is generally used for production.
This patch, also apparently fixes a workload at Google that Salman Qazi
reported by completely removing the poll_safewake_ncalls->lock from
wakeup paths.

Link: http://lkml.kernel.org/r/1507920533-8812-1-git-send-email-jbaron@akamai.com
Signed-off-by: Jason Baron <jbaron@akamai.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Salman Qazi <sqazi@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: account epitem and eppoll_entry to kmemcg

A userspace application can directly trigger the allocations from
eventpoll_epi and eventpoll_pwq slabs. A buggy or malicious application
can consume a significant amount of system memory by triggering such
allocations. Indeed we have seen in production where a buggy
application was leaking the epoll references and causing a burst of
eventpoll_epi and eventpoll_pwq slab allocations. This patch opt-in the
charging of eventpoll_epi and eventpoll_pwq slabs.

There is a per-user limit (~4% of total memory if no highmem) on these
caches. I think it is too generous particularly in the scenario where
jobs of multiple users are running on the system and the administrator
is reducing cost by overcomitting the memory. This is unaccounted
kernel memory and will not be considered by the oom-killer. I think by
accounting it to kmemcg, for systems with kmem accounting enabled, we
can provide better isolation between jobs of different users.

Link: http://lkml.kernel.org/r/20171003021519.23907-1-shakeelb@google.com
Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

get_compat_sigset()

similar to put_compat_sigset()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/epoll: use faster rb_first_cached()

... such that we can avoid the tree walks to get the node with the
smallest key. Semantically the same, as the previously used rb_first(),
but O(1). The main overhead is the extra footprint for the cached rb_node
pointer, which should not matter for epoll.

Link: http://lkml.kernel.org/r/20170719014603.19029-15-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove()

The race was introduced by me in commit 971316f0503a ("epoll:
ep_unregister_pollwait() can use the freed pwq->whead"). I did not
realize that nothing can protect eventpoll after ep_poll_callback() sets
->whead = NULL, only whead->lock can save us from the race with
ep_free() or ep_remove().

Move ->whead = NULL to the end of ep_poll_callback() and add the
necessary barriers.

TODO: cleanup the ewake/EPOLLEXCLUSIVE logic, it was confusing even
before this patch.

Hopefully this explains use-after-free reported by syzcaller:

BUG: KASAN: use-after-free in debug_spin_lock_before
...
_raw_spin_lock_irqsave+0x4a/0x60 kernel/locking/spinlock.c:159
ep_poll_callback+0x29f/0xff0 fs/eventpoll.c:1148

this is spin_lock(eventpoll->lock),

...
Freed by task 17774:
...
kfree+0xe8/0x2c0 mm/slub.c:3883
ep_free+0x22c/0x2a0 fs/eventpoll.c:865

Fixes: 971316f0503a ("epoll: ep_unregister_pollwait() can use the freed pwq->whead")
Reported-by: 范龙飞 <long7573@126.com>
Cc: stable@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kcmp: fs/epoll: wrap kcmp code with CONFIG_CHECKPOINT_RESTORE

kcmp syscall is build iif CONFIG_CHECKPOINT_RESTORE is selected, so wrap
appropriate helpers in epoll code with the config to build it
conditionally.

Link: http://lkml.kernel.org/r/20170513083456.GG1881@uranus.lan
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reported-by: Andrew Morton <akpm@linuxfoundation.org>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kcmp: add KCMP_EPOLL_TFD mode to compare epoll target files

With current epoll architecture target files are addressed with
file_struct and file descriptor number, where the last is not unique.
Moreover files can be transferred from another process via unix socket,
added into queue and closed then so we won't find this descriptor in the
task fdinfo list.

Thus to checkpoint and restore such processes CRIU needs to find out
where exactly the target file is present to add it into epoll queue.
For this sake one can use kcmp call where some particular target file
from the queue is compared with arbitrary file passed as an argument.

Because epoll target files can have same file descriptor number but
different file_struct a caller should explicitly specify the offset
within.

To test if some particular file is matching entry inside epoll one have
to

- fill kcmp_epoll_slot structure with epoll file descriptor,
target file number and target file offset (in case if only
one target is present then it should be 0)

- call kcmp as kcmp(pid1, pid2, KCMP_EPOLL_TFD, fd, &kcmp_epoll_slot)
- the kernel fetch file pointer matching file descriptor @fd of pid1
- lookups for file struct in epoll queue of pid2 and returns traditional
0,1,2 result for sorting purpose

Link: http://lkml.kernel.org/r/20170424154423.511592110@gmail.com
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

procfs: fdinfo: extend information about epoll target files

Since it is possbile to have same number in tfd field (say file added,
closed, then nother file dup'ed to same number and added back) it is
imposible to distinguish such target files solely by their numbers.

Strictly speaking regular applications don't need to recognize these
targets at all but for checkpoint/restore sake we need to collect
targets to be able to push them back on restore stage in a proper order.

Thus lets add file position, inode and device number where this target
lays. This three fields can be used as a primary key for sorting, and
together with kcmp help CRIU can find out an exact file target (from the
whole set of processes being checkpointed).

Link: http://lkml.kernel.org/r/20170424154423.436491881@gmail.com
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrei Vagin <avagin@virtuozzo.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs, epoll: short circuit fetching events if thread has been killed

We've encountered zombies that are waiting for a thread to exit that are
looping in ep_poll() almost endlessly although there is a pending
SIGKILL as a result of a group exit.

This happens because we always find ep_events_available() and fetch more
events and never are able to check for signal_pending() that would break
from the loop and return -EINTR.

Special case fatal signals and break immediately to guarantee that we
loop to fetch more events and delay making a timely exit.

It would also be possible to simply move the check for signal_pending()
higher than checking for ep_events_available(), but there have been no
reports of delayed signal handling other than SIGKILL preventing zombies
from exiting that would be fixed by this.

It fixes an issue for us where we have witnessed zombies sticking around
for at least O(minutes), but considering the code has been like this
forever and nobody else has complained that I have found, I would simply
queue it up for 4.12.

Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1705031722350.76784@chino.kir.corp.google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

sched/wait: Disambiguate wq_entry->task_list and wq_head->task_list naming

So I've noticed a number of instances where it was not obvious from the
code whether ->task_list was for a wait-queue head or a wait-queue entry.

Furthermore, there's a number of wait-queue users where the lists are
not for 'tasks' but other entities (poll tables, etc.), in which case
the 'task_list' name is actively confusing.

To clear this all up, name the wait-queue head and entry list structure
fields unambiguously:

struct wait_queue_head::task_list => ::head
struct wait_queue_entry::task_list => ::entry

For example, this code:

rqw->wait.task_list.next != &wait->task_list

... is was pretty unclear (to me) what it's doing, while now it's written this way:

rqw->wait.head.next != &wait->entry

... which makes it pretty clear that we are iterating a list until we see the head.

Other examples are:

list_for_each_entry_safe(pos, next, &x->task_list, task_list) {
list_for_each_entry(wq, &fence->wait.task_list, task_list) {

... where it's unclear (to me) what we are iterating, and during review it's
hard to tell whether it's trying to walk a wait-queue entry (which would be
a bug), while now it's written as:

list_for_each_entry_safe(pos, next, &x->head, entry) {
list_for_each_entry(wq, &fence->wait.head, entry) {

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

sched/wait: Rename wait_queue_t => wait_queue_entry_t

Rename:

wait_queue_t => wait_queue_entry_t

'wait_queue_t' was always a slight misnomer: its name implies that it's a "queue",
but in reality it's a queue *entry*. The 'real' queue is the wait queue head,
which had to carry the name.

Start sorting this out by renaming it to 'wait_queue_entry_t'.

This also allows the real structure name 'struct __wait_queue' to
lose its double underscore and become 'struct wait_queue_entry',
which is the more canonical nomenclature for such data types.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

epoll: Add busy poll support to epoll with socket fds.

This patch adds busy poll support to epoll. The implementation is meant to
be opportunistic in that it will take the NAPI ID from the last socket
that is added to the ready list that contains a valid NAPI ID and it will
use that for busy polling until the ready list goes empty. Once the ready
list goes empty the NAPI ID is reset and busy polling is disabled until a
new socket is added to the ready list.

In addition when we insert a new socket into the epoll we record the NAPI
ID and assume we are going to receive events on it. If that doesn't occur
it will be evicted as the active NAPI ID and we will resume normal
behavior.

An application can use SO_INCOMING_CPU or SO_REUSEPORT_ATTACH_C/EBPF socket
options to spread the incoming connections to specific worker threads
based on the incoming queue. This enables epoll for each worker thread
to have only sockets that receive packets from a single queue. So when an
application calls epoll_wait() and there are no events available to report,
busy polling is done on the associated queue to pull the packets.

Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h>

Fix up affected files that include this signal functionality via sched.h.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs,eventpoll: don't test for bitfield with stack value

In case if epoll_ctl is called with operation EPOLL_CTL_DEL then
@epds.events variable allocated on stack may contain random bits which
we test then for EPOLLEXCLUSIVE. Since currently the test look like

if (epds.events & EPOLLEXCLUSIVE) {
if (op == EPOLL_CTL_MOD)
goto error_tgt_fput;
if (op == EPOLL_CTL_ADD && (is_file_epoll(tf.file) ||
(epds.events & ~EPOLLEXCLUSIVE_OK_BITS)))
goto error_tgt_fput;
}

Nothing serious will happen even if epds.events has this bit set, still
better to be on safe side and make sure that we're to test this bit at
all.

Link: http://lkml.kernel.org/r/20170214154935.GG1850@uranus.lan
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Vagin <avagin@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Replace <asm/uaccess.h> with <linux/uaccess.h> globally

This was entirely automated, using the script by Al:

PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*<asm/uaccess.h>'
sed -i -e "s!$PATT!#include <linux/uaccess.h>!" \
$(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.

Requested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs: poll/select/recvmmsg: use timespec64 for timeout events

struct timespec is not y2038 safe. Even though timespec might be
sufficient to represent timeouts, use struct timespec64 here as the plan
is to get rid of all timespec reference in the kernel.

The patch transitions the common functions: poll_select_set_timeout()
and select_estimate_accuracy() to use timespec64. And, all the syscalls
that use these functions are transitioned in the same patch.

The restart block parameters for poll uses monotonic time. Use
timespec64 here as well to assign timeout value. This parameter in the
restart block need not change because this only holds the monotonic
timestamp at which timeout should occur. And, unsigned long data type
should be big enough for this timestamp.

The system call interfaces will be handled in a separate series.

Compat interfaces need not change as timespec64 is an alias to struct
timespec on a 64 bit system.

Link: http://lkml.kernel.org/r/1461947989-21926-3-git-send-email-deepa.kernel@gmail.com
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

timer: convert timer_slack_ns from unsigned long to u64

This patchset introduces a /proc/<pid>/timerslack_ns interface which
would allow controlling processes to be able to set the timerslack value
on other processes in order to save power by avoiding wakeups (Something
Android currently does via out-of-tree patches).

The first patch tries to fix the internal timer_slack_ns usage which was
defined as a long, which limits the slack range to ~4 seconds on 32bit
systems. It converts it to a u64, which provides the same basically
unlimited slack (500 years) on both 32bit and 64bit machines.

The second patch introduces the /proc/<pid>/timerslack_ns interface
which allows the full 64bit slack range for a task to be read or set on
both 32bit and 64bit machines.

With these two patches, on a 32bit machine, after setting the slack on
bash to 10 seconds:

$ time sleep 1

real 0m10.747s
user 0m0.001s
sys 0m0.005s

The first patch is a little ugly, since I had to chase the slack delta
arguments through a number of functions converting them to u64s. Let me
know if it makes sense to break that up more or not.

Other than that things are fairly straightforward.

This patch (of 2):

The timer_slack_ns value in the task struct is currently a unsigned
long. This means that on 32bit applications, the maximum slack is just
over 4 seconds. However, on 64bit machines, its much much larger (~500
years).

This disparity could make application development a little (as well as
the default_slack) to a u64. This means both 32bit and 64bit systems
have the same effective internal slack range.

Now the existing ABI via PR_GET_TIMERSLACK and PR_SET_TIMERSLACK specify
the interface as a unsigned long, so we preserve that limitation on
32bit systems, where SET_TIMERSLACK can only set the slack to a unsigned
long value, and GET_TIMERSLACK will return ULONG_MAX if the slack is
actually larger then what can be stored by an unsigned long.

This patch also modifies hrtimer functions which specified the slack
delta as a unsigned long.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Oren Laadan <orenl@cellrox.com>
Cc: Ruchi Kandoi <kandoiruchi@google.com>
Cc: Rom Lemarchand <romlem@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: restrict EPOLLEXCLUSIVE to POLLIN and POLLOUT

In the current implementation of the EPOLLEXCLUSIVE flag (added for
4.5-rc1), if epoll waiters create different POLL* sets and register them
as exclusive against the same target fd, the current implementation will
stop waking any further waiters once it finds the first idle waiter.
This means that waiters could miss wakeups in certain cases.

For example, when we wake up a pipe for reading we do:
wake_up_interruptible_sync_poll(&pipe->wait, POLLIN | POLLRDNORM); So if
one epoll set or epfd is added to pipe p with POLLIN and a second set
epfd2 is added to pipe p with POLLRDNORM, only epfd may receive the
wakeup since the current implementation will stop after it finds any
intersection of events with a waiter that is blocked in epoll_wait().

We could potentially address this by requiring all epoll waiters that
are added to p be required to pass the same set of POLL* events. IE the
first EPOLL_CTL_ADD that passes EPOLLEXCLUSIVE establishes the set POLL*
flags to be used by any other epfds that are added as EPOLLEXCLUSIVE.
However, I think it might be somewhat confusing interface as we would
have to reference count the number of users for that set, and so
userspace would have to keep track of that count, or we would need a
more involved interface. It also adds some shared state that we'd have
store somewhere. I don't think anybody will want to bloat
__wait_queue_head for this.

I think what we could do instead, is to simply restrict EPOLLEXCLUSIVE
such that it can only be specified with EPOLLIN and/or EPOLLOUT. So
that way if the wakeup includes 'POLLIN' and not 'POLLOUT', we can stop
once we hit the first idle waiter that specifies the EPOLLIN bit, since
any remaining waiters that only have 'POLLOUT' set wouldn't need to be
woken. Likewise, we can do the same thing if 'POLLOUT' is in the wakeup
bit set and not 'POLLIN'. If both 'POLLOUT' and 'POLLIN' are set in the
wake bit set (there is at least one example of this I saw in fs/pipe.c),
then we just wake the entire exclusive list. Having both 'POLLOUT' and
'POLLIN' both set should not be on any performance critical path, so I
think that's ok (in fs/pipe.c its in pipe_release()). We also continue
to include EPOLLERR and EPOLLHUP by default in any exclusive set. Thus,
the user can specify EPOLLERR and/or EPOLLHUP but is not required to do
so.

Since epoll waiters may be interested in other events as well besides
EPOLLIN, EPOLLOUT, EPOLLERR and EPOLLHUP, these can still be added by
doing a 'dup' call on the target fd and adding that as one normally
would with EPOLL_CTL_ADD. Since I think that the POLLIN and POLLOUT
events are what we are interest in balancing, I think that the 'dup'
thing could perhaps be added to only one of the waiter threads.
However, I think that EPOLLIN, EPOLLOUT, EPOLLERR and EPOLLHUP should be
sufficient for the majority of use-cases.

Since EPOLLEXCLUSIVE is intended to be used with a target fd shared
among multiple epfds, where between 1 and n of the epfds may receive an
event, it does not satisfy the semantics of EPOLLONESHOT where only 1
epfd would get an event. Thus, it is not allowed to be specified in
conjunction with EPOLLEXCLUSIVE.

EPOLL_CTL_MOD is also not allowed if the fd was previously added as
EPOLLEXCLUSIVE. It seems with the limited number of flags to not be as
interesting, but this could be relaxed at some further point.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Tested-by: Madars Vitolins <m@silodev.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: add EPOLLEXCLUSIVE flag

Currently, epoll file descriptors or epfds (the fd returned from
epoll_create[1]()) that are added to a shared wakeup source are always
added in a non-exclusive manner. This means that when we have multiple
epfds attached to a shared fd source they are all woken up. This creates
thundering herd type behavior.

Introduce a new 'EPOLLEXCLUSIVE' flag that can be passed as part of the
'event' argument during an epoll_ctl() EPOLL_CTL_ADD operation. This new
flag allows for exclusive wakeups when there are multiple epfds attached
to a shared fd event source.

The implementation walks the list of exclusive waiters, and queues an
event to each epfd, until it finds the first waiter that has threads
blocked on it via epoll_wait(). The idea is to search for threads which
are idle and ready to process the wakeup events. Thus, we queue an event
to at least 1 epfd, but may still potentially queue an event to all epfds
that are attached to the shared fd source.

Performance testing was done by Madars Vitolins using a modified version
of Enduro/X. The use of the 'EPOLLEXCLUSIVE' flag reduce the length of
this particular workload from 860s down to 24s.

Sample epoll_clt text:

EPOLLEXCLUSIVE

Sets an exclusive wakeup mode for the epfd file descriptor that is
being attached to the target file descriptor, fd. Thus, when an event
occurs and multiple epfd file descriptors are attached to the same
target file using EPOLLEXCLUSIVE, one or more epfds will receive an
event with epoll_wait(2). The default in this scenario (when
EPOLLEXCLUSIVE is not set) is for all epfds to receive an event.
EPOLLEXCLUSIVE may only be specified with the op EPOLL_CTL_ADD.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Tested-by: Madars Vitolins <m@silodev.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: optimize setting task running after blocking

After waking up a task waiting for an event, we explicitly mark it as
TASK_RUNNING (which is necessary as we do the checks for wakeups as
TASK_INTERRUPTIBLE). Once running and dealing with actually delivering
the events, we're obviously not planning on calling schedule, thus we can
relax the implied barrier and simply update the state with
__set_current_state().

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs: Convert show_fdinfo functions to void

seq_printf functions shouldn't really check the return value.
Checking seq_has_overflowed() occasionally is used instead.

Update vfs documentation.

Link: http://lkml.kernel.org/p/e37e6e7b76acbdcc3bb4ab2a57c8f8ca1ae11b9a.1412031505.git.joe@perches.com

Cc: David S. Miller <davem@davemloft.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Joe Perches <joe@perches.com>
[ did a few clean ups ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

eventpoll: fix uninitialized variable in epoll_ctl

When calling epoll_ctl with operation EPOLL_CTL_DEL, structure epds is
not initialized but ep_take_care_of_epollwakeup reads its event field.
When this unintialized field has EPOLLWAKEUP bit set, a capability check
is done for CAP_BLOCK_SUSPEND in ep_take_care_of_epollwakeup. This
produces unexpected messages in the audit log, such as (on a system
running SELinux):

type=AVC msg=audit(1408212798.866:410): avc: denied
{ block_suspend } for pid=7754 comm="dbus-daemon" capability=36
scontext=unconfined_u:unconfined_r:unconfined_t
tcontext=unconfined_u:unconfined_r:unconfined_t
tclass=capability2 permissive=1

type=SYSCALL msg=audit(1408212798.866:410): arch=c000003e syscall=233
success=yes exit=0 a0=3 a1=2 a2=9 a3=7fffd4d66ec0 items=0 ppid=1
pid=7754 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0
fsgid=0 tty=(none) ses=3 comm="dbus-daemon"
exe="/usr/bin/dbus-daemon"
subj=unconfined_u:unconfined_r:unconfined_t key=(null)

("arch=c000003e syscall=233 a1=2" means "epoll_ctl(op=EPOLL_CTL_DEL)")

Remove use of epds in epoll_ctl when op == EPOLL_CTL_DEL.

Fixes: 4d7e30d98939 ("epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready")
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix use-after-free in eventpoll_release_file

This fixes use-after-free of epi->fllink.next inside list loop macro.
This loop actually releases elements in the body. The list is
rcu-protected but here we cannot hold rcu_read_lock because we need to
lock mutex inside.

The obvious solution is to use list_for_each_entry_safe(). RCU-ness
isn't essential because nobody can change this list under us, it's final
fput for this file.

The bug was introduced by ae10b2b4eb01 ("epoll: optimize EPOLL_CTL_DEL
using rcu")

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Reported-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Stable <stable@vger.kernel.org> # 3.13+
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Jason Baron <jbaron@akamai.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs: convert use of typedef ctl_table to struct ctl_table

This typedef is unnecessary and should just be removed.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: do not take the nested ep->mtx on EPOLL_CTL_DEL

The EPOLL_CTL_DEL path of epoll contains a classic, ab-ba deadlock.
That is, epoll_ctl(a, EPOLL_CTL_DEL, b, x), will deadlock with
epoll_ctl(b, EPOLL_CTL_DEL, a, x). The deadlock was introduced with
commmit 67347fe4e632 ("epoll: do not take global 'epmutex' for simple
topologies").

The acquistion of the ep->mtx for the destination 'ep' was added such
that a concurrent EPOLL_CTL_ADD operation would see the correct state of
the ep (Specifically, the check for '!list_empty(&f.file->f_ep_links')

However, by simply not acquiring the lock, we do not serialize behind
the ep->mtx from the add path, and thus may perform a full path check
when if we had waited a little longer it may not have been necessary.
However, this is a transient state, and performing the full loop
checking in this case is not harmful.

The important point is that we wouldn't miss doing the full loop
checking when required, since EPOLL_CTL_ADD always locks any 'ep's that
its operating upon. The reason we don't need to do lock ordering in the
add path, is that we are already are holding the global 'epmutex'
whenever we do the double lock. Further, the original posting of this
patch, which was tested for the intended performance gains, did not
perform this additional locking.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: Nathan Zimmer <nzimmer@sgi.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Nelson Elhage <nelhage@nelhage.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: drop EPOLLWAKEUP if PM_SLEEP is disabled

Drop EPOLLWAKEUP from epoll events mask if CONFIG_PM_SLEEP is disabled.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

epoll: do not take global 'epmutex' for simple topologies

When calling EPOLL_CTL_ADD for an epoll file descriptor that is attached
directly to a wakeup source, we do not need to take the global 'epmutex',
unless the epoll file descriptor is nested. The purpose of taking the
'epmutex' on add is to prevent complex topologies such as loops and deep
wakeup paths from forming in parallel through multiple EPOLL_CTL_ADD
operations. However, for the simple case of an epoll file descriptor
attached directly to a wakeup source (with no nesting), we do not need to
hold the 'epmutex'.

This patch along with 'epoll: optimize EPOLL_CTL_DEL using rcu' improves
scalability on larger systems. Quoting Nathan Zimmer's mail on SPECjbb
performance:

"On the 16 socket run the performance went from 35k jOPS to 125k jOPS. In
addition the benchmark when from scaling well on 10 sockets to scaling
well on just over 40 sockets.

...

Currently the benchmark stops scaling at around 40-44 sockets but it seems like
I found a second unrelated bottleneck."

[akpm@linux-foundation.org: use `bool' for boolean variables, remove unneeded/undesirable cast of void*, add missed ep_scan_ready_list() kerneldoc]
Signed-off-by: Jason Baron <jbaron@akamai.com>
Tested-by: Nathan Zimmer <nzimmer@sgi.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Nelson Elhage <nelhage@nelhage.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: optimize EPOLL_CTL_DEL using rcu

Nathan Zimmer found that once we get over 10+ cpus, the scalability of
SPECjbb falls over due to the contention on the global 'epmutex', which is
taken in on EPOLL_CTL_ADD and EPOLL_CTL_DEL operations.

Patch #1 removes the 'epmutex' lock completely from the EPOLL_CTL_DEL path
by using rcu to guard against any concurrent traversals.

Patch #2 remove the 'epmutex' lock from EPOLL_CTL_ADD operations for
simple topologies. IE when adding a link from an epoll file descriptor to
a wakeup source, where the epoll file descriptor is not nested.

This patch (of 2):

Optimize EPOLL_CTL_DEL such that it does not require the 'epmutex' by
converting the file->f_ep_links list into an rcu one. In this way, we can
traverse the epoll network on the add path in parallel with deletes.
Since deletes can't create loops or worse wakeup paths, this is safe.

This patch in combination with the patch "epoll: Do not take global 'epmutex'
for simple topologies", shows a dramatic performance improvement in
scalability for SPECjbb.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Tested-by: Nathan Zimmer <nzimmer@sgi.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Nelson Elhage <nelhage@nelhage.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
CC: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Revert "epoll: use freezable blocking call"

This reverts commit 1c441e921201 (epoll: use freezable blocking call)
which is reported to cause user space memory corruption to happen
after suspend to RAM.

Since it appears to be extremely difficult to root cause this
problem, it is best to revert the offending commit and try to address
the original issue in a better way later.

References: https://bugzilla.kernel.org/show_bug.cgi?id=61781
Reported-by: Natrio <natrio@list.ru>
Reported-by: Jeff Pohlmeyer <yetanothergeek@gmail.com>
Bisected-by: Leo Wolf <jclw@ymail.com>
Fixes: 1c441e921201 (epoll: use freezable blocking call)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: 3.11+ <stable@vger.kernel.org> # 3.11+

file->f_op is never NULL...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: add a reschedule point in ep_free()

ep_free() might iterate on a huge set of epitems and hold cpu too long.
Add two cond_resched() in order to yield cpu to other tasks. This is safe
as we only hold mutexes in this function.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Theodore Ts'o <tytso@mit.edu>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

switch epoll_ctl() to fdget

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

signals: eventpoll: do not use sigprocmask()

sigprocmask() should die. None of the current callers actually
need this strange interface.

Change fs/eventpoll.c to use set_current_blocked(). This also
means we should not worry about SIGKILL/SIGSTOP.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eric Wong <normalperson@yhbt.net>
Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: use freezable blocking call

Avoid waking up every thread sleeping in an epoll_wait call during
suspend and resume by calling a freezable blocking call. Previous
patches modified the freezer to avoid sending wakeups to threads
that are blocked in freezable blocking calls.

This call was selected to be converted to a freezable call because
it doesn't hold any locks or release any resources when interrupted
that might be needed by another freezing task or a kernel driver
during suspend, and is a common site where idle userspace tasks are
blocked.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

epoll: cleanup: use RCU_INIT_POINTER when nulling

It is always safe to use RCU_INIT_POINTER to NULL a pointer. This results
in slightly smaller/faster code.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: cleanup: hoist out f_op->poll calls

This reduces the amount of code inside the ready list iteration loops for
better readability IMHO.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: lock ep->mtx in ep_free to silence lockdep

Technically we do not need to hold ep->mtx during ep_free since we are
certain there are no other users of ep at that point. However, lockdep
complains with a "suspicious rcu_dereference_check() usage!" message; so
lock the mutex before ep_remove to silence the warning.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: NeilBrown <neilb@suse.de>,
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: use RCU to protect wakeup_source in epitem

This prevents wakeup_source destruction when a user hits the item with
EPOLL_CTL_MOD while ep_poll_callback is running.

Tested with CONFIG_SPARSE_RCU_POINTER=y and "make fs/eventpoll.o C=2"

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: NeilBrown <neilb@suse.de>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: trim epitem by one cache line

It is common for epoll users to have thousands of epitems, so saving a
cache line on every allocation leads to large memory savings.

Since epitem allocations are cache-aligned, reducing sizeof(struct
epitem) from 136 bytes to 128 bytes will allow it to squeeze under a
cache line boundary on x86_64.

Via /sys/kernel/slab/eventpoll_epi, I see the following changes on my
x86_64 Core2 Duo (which has 64-byte cache alignment):

object_size : 192 => 128
objs_per_slab: 21 => 32

Also, add a BUILD_BUG_ON() to check for future accidental breakage.

[akpm@linux-foundation.org: use __packed, for all architectures]
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

switch epoll_pwait to COMPAT_SYSCALL_DEFINE

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: prevent missed events on EPOLL_CTL_MOD

EPOLL_CTL_MOD sets the interest mask before calling f_op->poll() to
ensure events are not missed. Since the modifications to the interest
mask are not protected by the same lock as ep_poll_callback, we need to
ensure the change is visible to other CPUs calling ep_poll_callback.

We also need to ensure f_op->poll() has an up-to-date view of past
events which occured before we modified the interest mask. So this
barrier also pairs with the barrier in wq_has_sleeper().

This should guarantee either ep_poll_callback or f_op->poll() (or both)
will notice the readiness of a recently-ready/modified item.

This issue was encountered by Andreas Voellmy and Junchang(Jason) Wang in:
http://thread.gmane.org/gmane.linux.kernel/1408782/

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Voellmy <andreas.voellmy@yale.edu>
Tested-by: "Junchang(Jason) Wang" <junchang.wang@yale.edu>
Cc: netdev@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs, epoll: add procfs fdinfo helper

This allows us to print out eventpoll target file descriptor, events and
data, the /proc/pid/fdinfo/fd consists of

| pos: 0
| flags: 02
| tfd: 5 events: 1d data: ffffffffffffffff enabled: 1

[avagin@: fix for unitialized ret variable]

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: James Bottomley <jbottomley@parallels.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Matthew Helsley <matt.helsley@gmail.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

revert "epoll: support for disabling items, and a self-test app"

Revert commit 03a7beb55b9f ("epoll: support for disabling items, and a
self-test app") pending resolution of the issues identified by Michael
Kerrisk, copied below.

We'll revisit this for 3.8.

: I've taken a look at this patch as it currently stands in 3.7-rc1, and
: done a bit of testing. (By the way, the test program
: tools/testing/selftests/epoll/test_epoll.c does not compile...)
:
: There are one or two places where the behavior seems a little strange,
: so I have a question or two at the end of this mail. But other than
: that, I want to check my understanding so that the interface can be
: correctly documented.
:
: Just to go though my understanding, the problem is the following
: scenario in a multithreaded application:
:
: 1. Multiple threads are performing epoll_wait() operations,
: and maintaining a user-space cache that contains information
: corresponding to each file descriptor being monitored by
: epoll_wait().
:
: 2. At some point, a thread wants to delete (EPOLL_CTL_DEL)
: a file descriptor from the epoll interest list, and
: delete the corresponding record from the user-space cache.
:
: 3. The problem with (2) is that some other thread may have
: previously done an epoll_wait() that retrieved information
: about the fd in question, and may be in the middle of using
: information in the cache that relates to that fd. Thus,
: there is a potential race.
:
: 4. The race can't solved purely in user space, because doing
: so would require applying a mutex across the epoll_wait()
: call, which would of course blow thread concurrency.
:
: Right?
:
: Your solution is the EPOLL_CTL_DISABLE operation. I want to
: confirm my understanding about how to use this flag, since
: the description that has accompanied the patches so far
: has been a bit sparse
:
: 0. In the scenario you're concerned about, deleting a file
: descriptor means (safely) doing the following:
: (a) Deleting the file descriptor from the epoll interest list
: using EPOLL_CTL_DEL
: (b) Deleting the corresponding record in the user-space cache
:
: 1. It's only meaningful to use this EPOLL_CTL_DISABLE in
: conjunction with EPOLLONESHOT.
:
: 2. Using EPOLL_CTL_DISABLE without using EPOLLONESHOT in
: conjunction is a logical error.
:
: 3. The correct way to code multithreaded applications using
: EPOLL_CTL_DISABLE and EPOLLONESHOT is as follows:
:
: a. All EPOLL_CTL_ADD and EPOLL_CTL_MOD operations should
: should EPOLLONESHOT.
:
: b. When a thread wants to delete a file descriptor, it
: should do the following:
:
: [1] Call epoll_ctl(EPOLL_CTL_DISABLE)
: [2] If the return status from epoll_ctl(EPOLL_CTL_DISABLE)
: was zero, then the file descriptor can be safely
: deleted by the thread that made this call.
: [3] If the epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY,
: then the descriptor is in use. In this case, the calling
: thread should set a flag in the user-space cache to
: indicate that the thread that is using the descriptor
: should perform the deletion operation.
:
: Is all of the above correct?
:
: The implementation depends on checking on whether
: (events & ~EP_PRIVATE_BITS) == 0
: This replies on the fact that EPOLL_CTL_AD and EPOLL_CTL_MOD always
: set EPOLLHUP and EPOLLERR in the 'events' mask, and EPOLLONESHOT
: causes those flags (as well as all others in ~EP_PRIVATE_BITS) to be
: cleared.
:
: A corollary to the previous paragraph is that using EPOLL_CTL_DISABLE
: is only useful in conjunction with EPOLLONESHOT. However, as things
: stand, one can use EPOLL_CTL_DISABLE on a file descriptor that does
: not have EPOLLONESHOT set in 'events' This results in the following
: (slightly surprising) behavior:
:
: (a) The first call to epoll_ctl(EPOLL_CTL_DISABLE) returns 0
: (the indicator that the file descriptor can be safely deleted).
: (b) The next call to epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY.
:
: This doesn't seem particularly useful, and in fact is probably an
: indication that the user made a logic error: they should only be using
: epoll_ctl(EPOLL_CTL_DISABLE) on a file descriptor for which
: EPOLLONESHOT was set in 'events'. If that is correct, then would it
: not make sense to return an error to user space for this case?

Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: "Paton J. Lewis" <palewis@adobe.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: support for disabling items, and a self-test app

Enhanced epoll_ctl to support EPOLL_CTL_DISABLE, which disables an epoll
item. If epoll_ctl doesn't return -EBUSY in this case, it is then safe to
delete the epoll item in a multi-threaded environment. Also added a new
test_epoll self- test app to both demonstrate the need for this feature
and test it.

Signed-off-by: Paton J. Lewis <palewis@adobe.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Paul Holland <pholland@adobe.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

switch simple cases of fget_light to fdget

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

switch epoll_wait(2) to fget_light()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

eventpoll: use-after-possible-free in epoll_create1()

As soon as we'd installed the file into descriptor table, it can
get closed by another thread. Freeing ep in process...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

PM: Rename CAP_EPOLLWAKEUP to CAP_BLOCK_SUSPEND

As discussed in
http://thread.gmane.org/gmane.linux.kernel/1249726/focus=1288990,
the capability introduced in 4d7e30d98939a0340022ccd49325a3d70f7e0238
to govern EPOLLWAKEUP seems misnamed: this capability is about governing
the ability to suspend the system, not using a particular API flag
(EPOLLWAKEUP). We should make the name of the capability more general
to encourage reuse in related cases. (Whether or not this capability
should also be used to govern the use of /sys/power/wake_lock is a
question that needs to be separately resolved.)

This patch renames the capability to CAP_BLOCK_SUSPEND. In order to ensure
that the old capability name doesn't make it out into the wild, could you
please apply and push up the tree to ensure that it is incorporated
for the 3.5 release.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

HAVE_RESTORE_SIGMASK is defined on all architectures now

Everyone either defines it in arch thread_info.h or has TIF_RESTORE_SIGMASK
and picks default set_restore_sigmask() in linux/thread_info.h. Kill the
ifdefs, slap #error in linux/thread_info.h to catch breakage when new ones
get merged.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

epoll: Fix user space breakage related to EPOLLWAKEUP

Commit 4d7e30d (epoll: Add a flag, EPOLLWAKEUP, to prevent
suspend while epoll events are ready) caused some applications to
malfunction, because they set the bit corresponding to the new
EPOLLWAKEUP flag in their eventpoll flags and they don't have the
new CAP_EPOLLWAKEUP capability.

To prevent that from happening, change epoll_ctl() to clear
EPOLLWAKEUP in epds.events if the caller doesn't have the
CAP_EPOLLWAKEUP capability instead of failing and returning an
error code, which allows the affected applications to function
normally.

Reported-and-tested-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready

When an epoll_event, that has the EPOLLWAKEUP flag set, is ready, a
wakeup_source will be active to prevent suspend. This can be used to
handle wakeup events from a driver that support poll, e.g. input, if
that driver wakes up the waitqueue passed to epoll before allowing
suspend.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

epoll: clear the tfile_check_list on -ELOOP

An epoll_ctl(,EPOLL_CTL_ADD,,) operation can return '-ELOOP' to prevent
circular epoll dependencies from being created. However, in that case we
do not properly clear the 'tfile_check_list'. Thus, add a call to
clear_tfile_check_list() for the -ELOOP case.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Reported-by: Yurij M. Plotnikov <Yurij.Plotnikov@oktetlabs.ru>
Cc: Nelson Elhage <nelhage@nelhage.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Tested-by: Alexandra N. Kossovsky <Alexandra.Kossovsky@oktetlabs.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Remove all #inclusions of asm/system.h

Remove all #inclusions of asm/system.h preparatory to splitting and killing
it. Performed with the following command:

perl -p -i -e 's!^#\s*include\s*<asm/system[.]h>.*\n!!' `grep -Irl '^#\s*include\s*<asm/system[.]h>' *`

Signed-off-by: David Howells <dhowells@redhat.com>

poll: add poll_requested_events() and poll_does_not_wait() functions

In some cases the poll() implementation in a driver has to do different
things depending on the events the caller wants to poll for. An example
is when a driver needs to start a DMA engine if the caller polls for
POLLIN, but doesn't want to do that if POLLIN is not requested but instead
only POLLOUT or POLLPRI is requested. This is something that can happen
in the video4linux subsystem among others.

Unfortunately, the current epoll/poll/select implementation doesn't
provide that information reliably. The poll_table_struct does have it: it
has a key field with the event mask. But once a poll() call matches one
or more bits of that mask any following poll() calls are passed a NULL
poll_table pointer.

Also, the eventpoll implementation always left the key field at ~0 instead
of using the requested events mask.

This was changed in eventpoll.c so the key field now contains the actual
events that should be polled for as set by the caller.

The solution to the NULL poll_table pointer is to set the qproc field to
NULL in poll_table once poll() matches the events, not the poll_table
pointer itself. That way drivers can obtain the mask through a new
poll_requested_events inline.

The poll_table_struct can still be NULL since some kernel code calls it
internally (netfs_state_poll() in ./drivers/staging/pohmelfs/netfs.h). In
that case poll_requested_events() returns ~0 (i.e. all events).

Very rarely drivers might want to know whether poll_wait will actually
wait. If another earlier file descriptor in the set already matched the
events the caller wanted to wait for, then the kernel will return from the
select() call without waiting. This might be useful information in order
to avoid doing expensive work.

A new helper function poll_does_not_wait() is added that drivers can use
to detect this situation. This is now used in sock_poll_wait() in
include/net/sock.h. This was the only place in the kernel that needed
this information.

Drivers should no longer access any of the poll_table internals, but use
the poll_requested_events() and poll_does_not_wait() access functions
instead. In order to enforce that the poll_table fields are now prepended
with an underscore and a comment was added warning against using them
directly.

This required a change in unix_dgram_poll() in unix/af_unix.c which used
the key field to get the requested events. It's been replaced by a call
to poll_requested_events().

For qproc it was especially important to change its name since the
behavior of that field changes with this patch since this function pointer
can now be NULL when that wasn't possible in the past.

Any driver accessing the qproc or key fields directly will now fail to compile.

Some notes regarding the correctness of this patch: the driver's poll()
function is called with a 'struct poll_table_struct *wait' argument. This
pointer may or may not be NULL, drivers can never rely on it being one or
the other as that depends on whether or not an earlier file descriptor in
the select()'s fdset matched the requested events.

There are only three things a driver can do with the wait argument:

1) obtain the key field:

events = wait ? wait->key : ~0;

This will still work although it should be replaced with the new
poll_requested_events() function (which does exactly the same).
This will now even work better, since wait is no longer set to NULL
unnecessarily.

2) use the qproc callback. This could be deadly since qproc can now be
NULL. Renaming qproc should prevent this from happening. There are no
kernel drivers that actually access this callback directly, BTW.

3) test whether wait == NULL to determine whether poll would return without
waiting. This is no longer sufficient as the correct test is now
wait == NULL || wait->_qproc == NULL.

However, the worst that can happen here is a slight performance hit in
the case where wait != NULL and wait->_qproc == NULL. In that case the
driver will assume that poll_wait() will actually add the fd to the set
of waiting file descriptors. Of course, poll_wait() will not do that
since it tests for wait->_qproc. This will not break anything, though.

There is only one place in the whole kernel where this happens
(sock_poll_wait() in include/net/sock.h) and that code will be replaced
by a call to poll_does_not_wait() in the next patch.

Note that even if wait->_qproc != NULL drivers cannot rely on poll_wait()
actually waiting. The next file descriptor from the set might match the
event mask and thus any possible waits will never happen.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Cc: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: remove unneeded variable in reverse_path_check()

We never use the length variable.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: comment the funky #ifdef

Looking for a bug in -rt, I stumbled across this code here from: commit
2dfa4eeab0fc ("epoll keyed wakeups: teach epoll about hints coming with
the wakeup key"), specifically:

#ifdef CONFIG_DEBUG_LOCK_ALLOC
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
unsigned long events, int subclass)
{
unsigned long flags;

spin_lock_irqsave_nested(&wqueue->lock, flags, subclass);
wake_up_locked_poll(wqueue, events);
spin_unlock_irqrestore(&wqueue->lock, flags);
}
#else
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
unsigned long events, int subclass)
{
wake_up_poll(wqueue, events);
}
#endif

You change the function of ep_wake_up_nested() depending on whether
CONFIG_DEBUG_LOCK_ALLOC is set or not. This looks awfully suspicious,
and there's no comment to explain why. I initially thought that this
was trying to fool lockdep, and hiding a real bug.

Investigating it, I found the creation of wake_up_nested() (which no
longer exists) but was created for the sole purpose of epoll and its
strange wake ups, as explained in commit 0ccf831cbee9 ("lockdep:
annotate epoll")

Although the commit message says "annotate epoll" the change log is much
better at explaining what is happening than what is in the actual code.
Thus a comment is really necessary here. And to save the time of other
developers from having to go trudging through the git logs trying to
figure out why this code exists.

I took parts of the change log and placed it into a comment above the
affected code. This will make the description of what is happening more
visible to new developers that have to look at this code for the first
time.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Don't limit non-nested epoll paths

Commit 28d82dc1c4ed ("epoll: limit paths") that I did to limit the
number of possible wakeup paths in epoll is causing a few applications
to longer work (dovecot for one).

The original patch is really about limiting the amount of epoll nesting
(since epoll fds can be attached to other fds). Thus, we probably can
allow an unlimited number of paths of depth 1. My current patch limits
it at 1000. And enforce the limits on paths that have a greater depth.

This is captured in: https://bugzilla.redhat.com/show_bug.cgi?id=681578

Signed-off-by: Jason Baron <jbaron@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: ep_unregister_pollwait() can use the freed pwq->whead

signalfd_cleanup() ensures that ->signalfd_wqh is not used, but
this is not enough. eppoll_entry->whead still points to the memory
we are going to free, ep_unregister_pollwait()->remove_wait_queue()
is obviously unsafe.

Change ep_poll_callback(POLLFREE) to set eppoll_entry->whead = NULL,
change ep_unregister_pollwait() to check pwq->whead != NULL under
rcu_read_lock() before remove_wait_queue(). We add the new helper,
ep_remove_wait_queue(), for this.

This works because sighand_cachep is SLAB_DESTROY_BY_RCU and because
->signalfd_wqh is initialized in sighand_ctor(), not in copy_sighand.
ep_unregister_pollwait()->remove_wait_queue() can play with already
freed and potentially reused ->sighand, but this is fine. This memory
must have the valid ->signalfd_wqh until rcu_read_unlock().

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Cc: <stable@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()

This patch is intentionally incomplete to simplify the review.
It ignores ep_unregister_pollwait() which plays with the same wqh.
See the next change.

epoll assumes that the EPOLL_CTL_ADD'ed file controls everything
f_op->poll() needs. In particular it assumes that the wait queue
can't go away until eventpoll_release(). This is not true in case
of signalfd, the task which does EPOLL_CTL_ADD uses its ->sighand
which is not connected to the file.

This patch adds the special event, POLLFREE, currently only for
epoll. It expects that init_poll_funcptr()'ed hook should do the
necessary cleanup. Perhaps it should be defined as EPOLLFREE in
eventpoll.

__cleanup_sighand() is changed to do wake_up_poll(POLLFREE) if
->signalfd_wqh is not empty, we add the new signalfd_cleanup()
helper.

ep_poll_callback(POLLFREE) simply does list_del_init(task_list).
This make this poll entry inconsistent, but we don't care. If you
share epoll fd which contains our sigfd with another process you
should blame yourself. signalfd is "really special". I simply do
not know how we can define the "right" semantics if it used with
epoll.

The main problem is, epoll calls signalfd_poll() once to establish
the connection with the wait queue, after that signalfd_poll(NULL)
returns the different/inconsistent results depending on who does
EPOLL_CTL_MOD/signalfd_read/etc. IOW: apart from sigmask, signalfd
has nothing to do with the file, it works with the current thread.

In short: this patch is the hack which tries to fix the symptoms.
It also assumes that nobody can take tasklist_lock under epoll
locks, this seems to be true.

Note:

- we do not have wake_up_all_poll() but wake_up_poll()
is fine, poll/epoll doesn't use WQ_FLAG_EXCLUSIVE.

- signalfd_cleanup() uses POLLHUP along with POLLFREE,
we need a couple of simple changes in eventpoll.c to
make sure it can't be "lost".

Reported-by: Maxime Bizon <mbizon@freebox.fr>
Cc: <stable@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: limit paths

The current epoll code can be tickled to run basically indefinitely in
both loop detection path check (on ep_insert()), and in the wakeup paths.
The programs that tickle this behavior set up deeply linked networks of
epoll file descriptors that cause the epoll algorithms to traverse them
indefinitely. A couple of these sample programs have been previously
posted in this thread: https://lkml.org/lkml/2011/2/25/297.

To fix the loop detection path check algorithms, I simply keep track of
the epoll nodes that have been already visited. Thus, the loop detection
becomes proportional to the number of epoll file descriptor and links.
This dramatically decreases the run-time of the loop check algorithm. In
one diabolical case I tried it reduced the run-time from 15 mintues (all
in kernel time) to .3 seconds.

Fixing the wakeup paths could be done at wakeup time in a similar manner
by keeping track of nodes that have already been visited, but the
complexity is harder, since there can be multiple wakeups on different
cpus...Thus, I've opted to limit the number of possible wakeup paths when
the paths are created.

This is accomplished, by noting that the end file descriptor points that
are found during the loop detection pass (from the newly added link), are
actually the sources for wakeup events. I keep a list of these file
descriptors and limit the number and length of these paths that emanate
from these 'source file descriptors'. In the current implemetation I
allow 1000 paths of length 1, 500 of length 2, 100 of length 3, 50 of
length 4 and 10 of length 5. Note that it is sufficient to check the
'source file descriptors' reachable from the newly added link, since no
other 'source file descriptors' will have newly added links. This allows
us to check only the wakeup paths that may have gotten too long, and not
re-check all possible wakeup paths on the system.

In terms of the path limit selection, I think its first worth noting that
the most common case for epoll, is probably the model where you have 1
epoll file descriptor that is monitoring n number of 'source file
descriptors'. In this case, each 'source file descriptor' has a 1 path of
length 1. Thus, I believe that the limits I'm proposing are quite
reasonable and in fact may be too generous. Thus, I'm hoping that the
proposed limits will not prevent any workloads that currently work to
fail.

In terms of locking, I have extended the use of the 'epmutex' to all
epoll_ctl add and remove operations. Currently its only used in a subset
of the add paths. I need to hold the epmutex, so that we can correctly
traverse a coherent graph, to check the number of paths. I believe that
this additional locking is probably ok, since its in the setup/teardown
paths, and doesn't affect the running paths, but it certainly is going to
add some extra overhead. Also, worth noting is that the epmuex was
recently added to the ep_ctl add operations in the initial path loop
detection code using the argument that it was not on a critical path.

Another thing to note here, is the length of epoll chains that is allowed.
Currently, eventpoll.c defines:

/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4

This basically means that I am limited to a graph depth of 5 (EP_MAX_NESTS
+ 1). However, this limit is currently only enforced during the loop
check detection code, and only when the epoll file descriptors are added
in a certain order. Thus, this limit is currently easily bypassed. The
newly added check for wakeup paths, stricly limits the wakeup paths to a
length of 5, regardless of the order in which ep's are linked together.
Thus, a side-effect of the new code is a more consistent enforcement of
the graph depth.

Thus far, I've tested this, using the sample programs previously
mentioned, which now either return quickly or return -EINVAL. I've also
testing using the piptest.c epoll tester, which showed no difference in
performance. I've also created a number of different epoll networks and
tested that they behave as expectded.

I believe this solves the original diabolical test cases, while still
preserving the sane epoll nesting.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Cc: Nelson Elhage <nelhage@ksplice.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix spurious lockdep warnings

epoll can acquire recursively acquire ep->mtx on multiple "struct
eventpoll"s at once in the case where one epoll fd is monitoring another
epoll fd. This is perfectly OK, since we're careful about the lock
ordering, but it causes spurious lockdep warnings. Annotate the recursion
using mutex_lock_nested, and add a comment explaining the nesting rules
for good measure.

Recent versions of systemd are triggering this, and it can also be
demonstrated with the following trivial test program:

--------------------8<--------------------

int main(void) {
int e1, e2;
struct epoll_event evt = {
.events = EPOLLIN
};

e1 = epoll_create1(0);
e2 = epoll_create1(0);
epoll_ctl(e1, EPOLL_CTL_ADD, e2, &evt);
return 0;
}
--------------------8<--------------------

Reported-by: Paul Bolle <pebolle@tiscali.nl>
Tested-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
Acked-by: Jason Baron <jbaron@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

atomic: use <linux/atomic.h>

This allows us to move duplicated code in <asm/atomic.h>
(atomic_inc_not_zero() for now) to <linux/atomic.h>

Signed-off-by: Arun Sharma <asharma@fb.com>
Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

eventpoll: fix comment typo 'evenpoll'

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>

epoll: fix compiler warning and optimize the non-blocking path

Add a comment to ep_poll(), rename labels a bit clearly, fix a warning of
unused variable from gcc and optimize the non-blocking path a little.

Hinted-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>

hannes@cmpxchg.org:

: The non-blocking ep_poll path optimization introduced skipping over the
: return value setup.
:
: Initialize it properly, my userspace gets upset by epoll_wait() returning
: random things.
:
: In addition, remove the reinitialization at the fetch_events label, the
: return value is garuanteed to be zero when execution reaches there.

[hannes@cmpxchg.org: fix initialization]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: move ready event check into proper inline

Move the event readiness check into a proper inline, and use it uniformly
inside ep_poll() code. Events in the ->ovflist are no less ready than the
ones in ->rdllist.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: prevent creating circular epoll structures

In several places, an epoll fd can call another file's ->f_op->poll()
method with ep->mtx held. This is in general unsafe, because that other
file could itself be an epoll fd that contains the original epoll fd.

The code defends against this possibility in its own ->poll() method using
ep_call_nested, but there are several other unsafe calls to ->poll
elsewhere that can be made to deadlock. For example, the following simple
program causes the call in ep_insert recursively call the original fd's
->poll, leading to deadlock:

#include <unistd.h>
#include <sys/epoll.h>

int main(void) {
int e1, e2, p[2];
struct epoll_event evt = {
.events = EPOLLIN
};

e1 = epoll_create(1);
e2 = epoll_create(2);
pipe(p);

epoll_ctl(e2, EPOLL_CTL_ADD, e1, &evt);
epoll_ctl(e1, EPOLL_CTL_ADD, p[0], &evt);
write(p[1], p, sizeof p);
epoll_ctl(e1, EPOLL_CTL_ADD, e2, &evt);

return 0;
}

On insertion, check whether the inserted file is itself a struct epoll,
and if so, do a recursive walk to detect whether inserting this file would
create a loop of epoll structures, which could lead to deadlock.

[nelhage@ksplice.com: Use epmutex to serialize concurrent inserts]
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Nelson Elhage <nelhage@ksplice.com>
Reported-by: Nelson Elhage <nelhage@ksplice.com>
Tested-by: Nelson Elhage <nelhage@ksplice.com>
Cc: <stable@kernel.org> [2.6.34+, possibly earlier]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventpoll.c: fix spelling

eventpoll.c has wonderful comments but some annoying typos
sneaked in:
* toepoll_ctl -> to epoll_ctl
* rapresent -> represents
* sructure -> structure
* machanism -> mechanism
* trasfering -> transferring

Signed-off-by: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

epoll: epoll_wait() should not use timespec_add_ns()

commit 95aac7b1cd224f ("epoll: make epoll_wait() use the hrtimer range
feature") added a performance regression because it uses timespec_add_ns()
with potential very large 'ns' values.

[akpm@linux-foundation.org: s/epoll_set_mstimeout/ep_set_mstimeout/, per Davide]
Reported-by: Simon Kirby <sim@hostway.ca>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <stable@kernel.org> [2.6.37.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: convert max_user_watches to long

On a 16TB machine, max_user_watches has an integer overflow. Convert it
to use a long and handle the associated fallout.

Signed-off-by: Robin Holt <holt@sgi.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: make epoll_wait() use the hrtimer range feature

This make epoll use hrtimers for the timeout value which prevents
epoll_wait() from timing out up to a millisecond early.

This mirrors the behavior of select() and poll().

Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

llseek: automatically add .llseek fop

All file_operations should get a .llseek operation so we can make
nonseekable_open the default for future file operations without a
.llseek pointer.

The three cases that we can automatically detect are no_llseek, seq_lseek
and default_llseek. For cases where we can we can automatically prove that
the file offset is always ignored, we use noop_llseek, which maintains
the current behavior of not returning an error from a seek.

New drivers should normally not use noop_llseek but instead use no_llseek
and call nonseekable_open at open time. Existing drivers can be converted
to do the same when the maintainer knows for certain that no user code
relies on calling seek on the device file.

The generated code is often incorrectly indented and right now contains
comments that clarify for each added line why a specific variant was
chosen. In the version that gets submitted upstream, the comments will
be gone and I will manually fix the indentation, because there does not
seem to be a way to do that using coccinelle.

Some amount of new code is currently sitting in linux-next that should get
the same modifications, which I will do at the end of the merge window.

Many thanks to Julia Lawall for helping me learn to write a semantic
patch that does all this.

===== begin semantic patch =====
// This adds an llseek= method to all file operations,
// as a preparation for making no_llseek the default.
//
// The rules are
// - use no_llseek explicitly if we do nonseekable_open
// - use seq_lseek for sequential files
// - use default_llseek if we know we access f_pos
// - use noop_llseek if we know we don't access f_pos,
// but we still want to allow users to call lseek
//
@ open1 exists @
identifier nested_open;
@@
nested_open(...)
{
<+...
nonseekable_open(...)
...+>
}

@ open exists@
identifier open_f;
identifier i, f;
identifier open1.nested_open;
@@
int open_f(struct inode *i, struct file *f)
{
<+...
(
nonseekable_open(...)
|
nested_open(...)
)
...+>
}

@ read disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{
<+...
(
*off = E
|
*off += E
|
func(..., off, ...)
|
E = *off
)
...+>
}

@ read_no_fpos disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{
... when != off
}

@ write @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{
<+...
(
*off = E
|
*off += E
|
func(..., off, ...)
|
E = *off
)
...+>
}

@ write_no_fpos @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{
... when != off
}

@ fops0 @
identifier fops;
@@
struct file_operations fops = {
...
};

@ has_llseek depends on fops0 @
identifier fops0.fops;
identifier llseek_f;
@@
struct file_operations fops = {
...
.llseek = llseek_f,
...
};

@ has_read depends on fops0 @
identifier fops0.fops;
identifier read_f;
@@
struct file_operations fops = {
...
.read = read_f,
...
};

@ has_write depends on fops0 @
identifier fops0.fops;
identifier write_f;
@@
struct file_operations fops = {
...
.write = write_f,
...
};

@ has_open depends on fops0 @
identifier fops0.fops;
identifier open_f;
@@
struct file_operations fops = {
...
.open = open_f,
...
};

// use no_llseek if we call nonseekable_open
////////////////////////////////////////////
@ nonseekable1 depends on !has_llseek && has_open @
identifier fops0.fops;
identifier nso ~= "nonseekable_open";
@@
struct file_operations fops = {
... .open = nso, ...
+.llseek = no_llseek, /* nonseekable */
};

@ nonseekable2 depends on !has_llseek @
identifier fops0.fops;
identifier open.open_f;
@@
struct file_operations fops = {
... .open = open_f, ...
+.llseek = no_llseek, /* open uses nonseekable */
};

// use seq_lseek for sequential files
/////////////////////////////////////
@ seq depends on !has_llseek @
identifier fops0.fops;
identifier sr ~= "seq_read";
@@
struct file_operations fops = {
... .read = sr, ...
+.llseek = seq_lseek, /* we have seq_read */
};

// use default_llseek if there is a readdir
///////////////////////////////////////////
@ fops1 depends on !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier readdir_e;
@@
// any other fop is used that changes pos
struct file_operations fops = {
... .readdir = readdir_e, ...
+.llseek = default_llseek, /* readdir is present */
};

// use default_llseek if at least one of read/write touches f_pos
/////////////////////////////////////////////////////////////////
@ fops2 depends on !fops1 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read.read_f;
@@
// read fops use offset
struct file_operations fops = {
... .read = read_f, ...
+.llseek = default_llseek, /* read accesses f_pos */
};

@ fops3 depends on !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write.write_f;
@@
// write fops use offset
struct file_operations fops = {
... .write = write_f, ...
+ .llseek = default_llseek, /* write accesses f_pos */
};

// Use noop_llseek if neither read nor write accesses f_pos
///////////////////////////////////////////////////////////

@ fops4 depends on !fops1 && !fops2 && !fops3 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
identifier write_no_fpos.write_f;
@@
// write fops use offset
struct file_operations fops = {
...
.write = write_f,
.read = read_f,
...
+.llseek = noop_llseek, /* read and write both use no f_pos */
};

@ depends on has_write && !has_read && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write_no_fpos.write_f;
@@
struct file_operations fops = {
... .write = write_f, ...
+.llseek = noop_llseek, /* write uses no f_pos */
};

@ depends on has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
@@
struct file_operations fops = {
... .read = read_f, ...
+.llseek = noop_llseek, /* read uses no f_pos */
};

@ depends on !has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
@@
struct file_operations fops = {
...
+.llseek = noop_llseek, /* no read or write fn */
};
===== End semantic patch =====

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Julia Lawall <julia@diku.dk>
Cc: Christoph Hellwig <hch@infradead.org>

sched, wait: Use wrapper functions

epoll should not touch flags in wait_queue_t. This patch introduces a new
function __add_wait_queue_exclusive(), for the users, who use wait queue as a
LIFO queue.

__add_wait_queue_tail_exclusive() is introduced too instead of
add_wait_queue_exclusive_locked(). remove_wait_queue_locked() is removed, as
it is a duplicate of __remove_wait_queue(), disliked by users, and with less
users.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: <containers@lists.linux-foundation.org>
LKML-Reference: <1273214006-2979-1-git-send-email-xiaosuo@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

anonfd: Allow making anon files read-only

It seems a couple places such as arch/ia64/kernel/perfmon.c and
drivers/infiniband/core/uverbs_main.c could use anon_inode_getfile()
instead of a private pseudo-fs + alloc_file(), if only there were a way
to get a read-only file. So provide this by having anon_inode_getfile()
create a read-only file if we pass O_RDONLY in flags.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

sysctl: Drop & in front of every proc_handler.

For consistency drop & in front of every proc_handler. Explicity
taking the address is unnecessary and it prevents optimizations
like stubbing the proc_handlers to NULL.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

sysctl fs: Remove dead binary sysctl support

Now that sys_sysctl is a generic wrapper around /proc/sys .ctl_name
and .strategy members of sysctl tables are dead code. Remove them.

Cc: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

epoll: fix nested calls support

This fixes a regression in 2.6.30.

I unfortunately accepted a patch time ago, to drop the "current" usage
from possible IRQ context, w/out proper thought over it. The patch
switched to using the CPU id by bounding the nested call callback with a
get_cpu()/put_cpu().

Unfortunately the ep_call_nested() function can be called with a callback
that grabs sleepy locks (from own f_op->poll()), that results in epic
fails. The following patch uses the proper "context" depending on the
path where it is called, and on the kind of callback.

This has been reported by Stefan Richter, that has also verified the patch
is his previously failing environment.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix size check in epoll_create()

Fix a size check WRT the manual pages. This was inadvertently broken by
commit 9fe5ad9c8cef9ad5873d8ee55d1cf00d9b607df0 ("flag parameters
add-on: remove epoll_create size param").

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: <Hiroyuki.Mach@gmail.com>
Cc: rohit verma <rohit.170309@gmail.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll keyed wakeups: teach epoll about hints coming with the wakeup key

Use the events hint now sent by some devices, to avoid unnecessary wakeups
for events that are of no interest for the caller. This code handles both
devices that are sending keyed events, and the ones that are not (and
event the ones that sometimes send events, and sometimes don't).

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David Miller <davem@davemloft.net>
Cc: William Lee Irwin III <wli@movementarian.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: use real type instead of void *

eventpoll.c uses void * in one place for no obvious reason; change it to
use the real type instead.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: clean up ep_modify

ep_modify() doesn't need to set event.data from within the ep->lock
spinlock as the comment suggests. The only place event.data is used is
ep_send_events_proc(), and this is protected by ep->mtx instead of
ep->lock. Also update the comment for mutex_lock() at the top of
ep_scan_ready_list(), which mentions epoll_ctl(EPOLL_CTL_DEL) but not
epoll_ctl(EPOLL_CTL_MOD).

ep_modify() can also use spin_lock_irq() instead of spin_lock_irqsave().

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: remove unnecessary xchg

xchg in ep_unregister_pollwait() is unnecessary because it is protected by
either epmutex or ep->mtx (the same protection as ep_remove()).

If xchg was necessary, it would be insufficient to protect against
problems: if multiple concurrent calls to ep_unregister_pollwait() were
possible then a second caller that returns without doing anything because
nwait == 0 could return before the waitqueues are removed by the first
caller, which looks like it could lead to problematic races with
ep_poll_callback().

So remove xchg and add comments about the locking.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: remember the event if epoll_wait returns -EFAULT

If epoll_wait returns -EFAULT, the event that was being returned when the
fault was encountered will be forgotten. This is not a big deal since
EFAULT will happen only if a buggy userspace program passes in a bad
address, in which case what happens later usually doesn't matter.
However, it is easy to remember the event for later, and this patch makes
a simple change to do that.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: don't use current in irq context

ep_call_nested() (formerly ep_poll_safewake()) uses "current" (without
dereferencing it) to detect callback recursion, but it may be called from
irq context where the use of current is generally discouraged. It would
be better to use get_cpu() and put_cpu() to detect the callback recursion.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: remove debugging code

Remove debugging code from epoll. There's no need for it to be included
into mainline code.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix epoll's own poll (update)

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: fix epoll's own poll

Fix a bug inside the epoll's f_op->poll() code, that returns POLLIN even
though there are no actual ready monitored fds. The bug shows up if you
add an epoll fd inside another fd container (poll, select, epoll).

The problem is that callback-based wake ups used by epoll does not carry
(patches will follow, to fix this) any information about the events that
actually happened. So the callback code, since it can't call the file*
->poll() inside the callback, chains the file* into a ready-list.

So, suppose you added an fd with EPOLLOUT only, and some data shows up on
the fd, the file* mapped by the fd will be added into the ready-list (via
wakeup callback). During normal epoll_wait() use, this condition is
sorted out at the time we're actually able to call the file*'s
f_op->poll().

Inside the old epoll's f_op->poll() though, only a quick check
!list_empty(ready-list) was performed, and this could have led to
reporting POLLIN even though no ready fds would show up at a following
epoll_wait(). In order to correctly report the ready status for an epoll
fd, the ready-list must be checked to see if any really available fd+event
would be ready in a following epoll_wait().

Operation (calling f_op->poll() from inside f_op->poll()) that, like wake
ups, must be handled with care because of the fact that epoll fds can be
added to other epoll fds.

Test code:

/*
* epoll_test by Davide Libenzi (Simple code to test epoll internals)
* Copyright (C) 2008 Davide Libenzi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Davide Libenzi <davidel@xmailserver.org>
*
*/

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <limits.h>
#include <poll.h>
#include <sys/epoll.h>
#include <sys/wait.h>

#define EPWAIT_TIMEO (1 * 1000)
#ifndef POLLRDHUP
#define POLLRDHUP 0x2000
#endif

#define EPOLL_MAX_CHAIN 100L

#define EPOLL_TF_LOOP (1 << 0)

struct epoll_test_cfg {
long size;
long flags;
};

static int xepoll_create(int n) {
int epfd;

if ((epfd = epoll_create(n)) == -1) {
perror("epoll_create");
exit(2);
}

return epfd;
}

static void xepoll_ctl(int epfd, int cmd, int fd, struct epoll_event *evt) {
if (epoll_ctl(epfd, cmd, fd, evt) < 0) {
perror("epoll_ctl");
exit(3);
}
}

static void xpipe(int *fds) {
if (pipe(fds)) {
perror("pipe");
exit(4);
}
}

static pid_t xfork(void) {
pid_t pid;

if ((pid = fork()) == (pid_t) -1) {
perror("pipe");
exit(5);
}

return pid;
}

static int run_forked_proc(int (*proc)(void *), void *data) {
int status;
pid_t pid;

if ((pid = xfork()) == 0)
exit((*proc)(data));
if (waitpid(pid, &status, 0) != pid) {
perror("waitpid");
return -1;
}

return WIFEXITED(status) ? WEXITSTATUS(status): -2;
}

static int check_events(int fd, int timeo) {
struct pollfd pfd;

fprintf(stdout, "Checking events for fd %d\n", fd);
memset(&pfd, 0, sizeof(pfd));
pfd.fd = fd;
pfd.events = POLLIN | POLLOUT;
if (poll(&pfd, 1, timeo) < 0) {
perror("poll()");
return 0;
}
if (pfd.revents & POLLIN)
fprintf(stdout, "\tPOLLIN\n");
if (pfd.revents & POLLOUT)
fprintf(stdout, "\tPOLLOUT\n");
if (pfd.revents & POLLERR)
fprintf(stdout, "\tPOLLERR\n");
if (pfd.revents & POLLHUP)
fprintf(stdout, "\tPOLLHUP\n");
if (pfd.revents & POLLRDHUP)
fprintf(stdout, "\tPOLLRDHUP\n");

return pfd.revents;
}

static int epoll_test_tty(void *data) {
int epfd, ifd = fileno(stdin), res;
struct epoll_event evt;

if (check_events(ifd, 0) != POLLOUT) {
fprintf(stderr, "Something is cooking on STDIN (%d)\n", ifd);
return 1;
}
epfd = xepoll_create(1);
fprintf(stdout, "Created epoll fd (%d)\n", epfd);
memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;
xepoll_ctl(epfd, EPOLL_CTL_ADD, ifd, &evt);
if (check_events(epfd, 0) & POLLIN) {
res = epoll_wait(epfd, &evt, 1, 0);
if (res == 0) {
fprintf(stderr, "Epoll fd (%d) is ready when it shouldn't!\n",
epfd);
return 2;
}
}

return 0;
}

static int epoll_wakeup_chain(void *data) {
struct epoll_test_cfg *tcfg = data;
int i, res, epfd, bfd, nfd, pfds[2];
pid_t pid;
struct epoll_event evt;

memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;

epfd = bfd = xepoll_create(1);

for (i = 0; i < tcfg->size; i++) {
nfd = xepoll_create(1);
xepoll_ctl(bfd, EPOLL_CTL_ADD, nfd, &evt);
bfd = nfd;
}
xpipe(pfds);
if (tcfg->flags & EPOLL_TF_LOOP)
{
xepoll_ctl(bfd, EPOLL_CTL_ADD, epfd, &evt);
/*
* If we're testing for loop, we want that the wakeup
* triggered by the write to the pipe done in the child
* process, triggers a fake event. So we add the pipe
* read size with EPOLLOUT events. This will trigger
* an addition to the ready-list, but no real events
* will be there. The the epoll kernel code will proceed
* in calling f_op->poll() of the epfd, triggering the
* loop we want to test.
*/
evt.events = EPOLLOUT;
}
xepoll_ctl(bfd, EPOLL_CTL_ADD, pfds[0], &evt);

/*
* The pipe write must come after the poll(2) call inside
* check_events(). This tests the nested wakeup code in
* fs/eventpoll.c:ep_poll_safewake()
* By having the check_events() (hence poll(2)) happens first,
* we have poll wait queue filled up, and the write(2) in the
* child will trigger the wakeup chain.
*/
if ((pid = xfork()) == 0) {
sleep(1);
write(pfds[1], "w", 1);
exit(0);
}

res = check_events(epfd, 2000) & POLLIN;

if (waitpid(pid, NULL, 0) != pid) {
perror("waitpid");
return -1;
}

return res;
}

static int epoll_poll_chain(void *data) {
struct epoll_test_cfg *tcfg = data;
int i, res, epfd, bfd, nfd, pfds[2];
pid_t pid;
struct epoll_event evt;

memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;

epfd = bfd = xepoll_create(1);

for (i = 0; i < tcfg->size; i++) {
nfd = xepoll_create(1);
xepoll_ctl(bfd, EPOLL_CTL_ADD, nfd, &evt);
bfd = nfd;
}
xpipe(pfds);
if (tcfg->flags & EPOLL_TF_LOOP)
{
xepoll_ctl(bfd, EPOLL_CTL_ADD, epfd, &evt);
/*
* If we're testing for loop, we want that the wakeup
* triggered by the write to the pipe done in the child
* process, triggers a fake event. So we add the pipe
* read size with EPOLLOUT events. This will trigger
* an addition to the ready-list, but no real events
* will be there. The the epoll kernel code will proceed
* in calling f_op->poll() of the epfd, triggering the
* loop we want to test.
*/
evt.events = EPOLLOUT;
}
xepoll_ctl(bfd, EPOLL_CTL_ADD, pfds[0], &evt);

/*
* The pipe write mush come before the poll(2) call inside
* check_events(). This tests the nested f_op->poll calls code in
* fs/eventpoll.c:ep_eventpoll_poll()
* By having the pipe write(2) happen first, we make the kernel
* epoll code to load the ready lists, and the following poll(2)
* done inside check_events() will test nested poll code in
* ep_eventpoll_poll().
*/
if ((pid = xfork()) == 0) {
write(pfds[1], "w", 1);
exit(0);
}
sleep(1);
res = check_events(epfd, 1000) & POLLIN;

if (waitpid(pid, NULL, 0) != pid) {
perror("waitpid");
return -1;
}

return res;
}

int main(int ac, char **av) {
int error;
struct epoll_test_cfg tcfg;

fprintf(stdout, "\n********** Testing TTY events\n");
error = run_forked_proc(epoll_test_tty, NULL);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing short wakeup chain\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == POLLIN ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = EPOLL_MAX_CHAIN;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing long wakeup chain (HOLD ON)\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing short poll chain\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == POLLIN ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = EPOLL_MAX_CHAIN;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing long poll chain (HOLD ON)\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = EPOLL_TF_LOOP;
fprintf(stdout, "\n********** Testing loopy wakeup chain (HOLD ON)\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = EPOLL_TF_LOOP;
fprintf(stdout, "\n********** Testing loopy poll chain (HOLD ON)\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

return 0;
}

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Rename struct file->f_ep_lock

This lock moves out of the CONFIG_EPOLL ifdef and becomes f_lock. For now,
epoll remains the only user, but a future patch will use it to protect
f_flags as well.

Cc: Davide Libenzi <davidel@xmailserver.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

epoll: drop max_user_instances and rely only on max_user_watches

Linus suggested to put limits where the money is, and max_user_watches
already does that w/out the need of max_user_instances. That has the
advantage to mitigate the potential DoS while allowing pretty generous
default behavior.

Allowing top 4% of low memory (per user) to be allocated in epoll watches,
we have:

LOMEM MAX_WATCHES (per user)
512MB ~178000
1GB ~356000
2GB ~712000

A box with 512MB of lomem, will meet some challenge in hitting 180K
watches, socket buffers math teaches us. No more max_user_instances
limits then.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Bron Gondwana <brong@fastmail.fm>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

[CVE-2009-0029] System call wrappers part 23

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

epoll: introduce resource usage limits

It has been thought that the per-user file descriptors limit would also
limit the resources that a normal user can request via the epoll
interface. Vegard Nossum reported a very simple program (a modified
version attached) that can make a normal user to request a pretty large
amount of kernel memory, well within the its maximum number of fds. To
solve such problem, default limits are now imposed, and /proc based
configuration has been introduced. A new directory has been created,
named /proc/sys/fs/epoll/ and inside there, there are two configuration
points:

max_user_instances = Maximum number of devices - per user

max_user_watches = Maximum number of "watched" fds - per user

The current default for "max_user_watches" limits the memory used by epoll
to store "watches", to 1/32 of the amount of the low RAM. As example, a
256MB 32bit machine, will have "max_user_watches" set to roughly 90000.
That should be enough to not break existing heavy epoll users. The
default value for "max_user_instances" is set to 128, that should be
enough too.

This also changes the userspace, because a new error code can now come out
from EPOLL_CTL_ADD (-ENOSPC). The EMFILE from epoll_create() was already
listed, so that should be ok.

[akpm@linux-foundation.org: use get_current_user()]
Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: <stable@kernel.org>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Reported-by: Vegard Nossum <vegardno@ifi.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: avoid double-inserts in case of EFAULT

In commit f337b9c58332bdecde965b436e47ea4c94d30da0 ("epoll: drop
unnecessary test") Thomas found that there is an unnecessary (always
true) test in ep_send_events(). The callback never inserts into
->rdllink while the send loop is performed, and also does the
~EP_PRIVATE_BITS test. Given we're holding the mutex during this time,
the conditions tested inside the loop are always true.

HOWEVER.

The test "!ep_is_linked(&epi->rdllink)" wasn't there because we insert
into ->rdllink, but because the send-events loop might terminate before
the whole list is scanned (-EFAULT).

In such cases, when the loop terminates early, and when a (leftover)
file received an event while we're performing the lockless loop, we need
such test to avoid to double insert the epoll items. The list_splice()
done a few steps below, will correctly re-insert the ones that were left
on "txlist".

This should fix the kenrel.org bugzilla entry 11831.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

epoll: drop unnecessary test

Thomas found that there is an unnecessary (always true) test in
ep_send_events(). The callback never inserts into ->rdllink while the
send loop is performed, and also does the ~EP_PRIVATE_BITS test. Given
we're holding the mutex during this time, the conditions tested inside the
loop are always true. This patch drops the test done inside the
re-insertion loop.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/eventpoll.c: fix sys_epoll_create1() comment

The `size' argument was removed.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>