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H A Dfile.cdiff 147e1a97 Tue Mar 05 16:45:45 MST 2019 Johannes Weiner <hannes@cmpxchg.org> fs: kernfs: add poll file operation

Patch series "psi: pressure stall monitors", v3.

Android is adopting psi to detect and remedy memory pressure that
results in stuttering and decreased responsiveness on mobile devices.

Psi gives us the stall information, but because we're dealing with
latencies in the millisecond range, periodically reading the pressure
files to detect stalls in a timely fashion is not feasible. Psi also
doesn't aggregate its averages at a high enough frequency right now.

This patch series extends the psi interface such that users can
configure sensitive latency thresholds and use poll() and friends to be
notified when these are breached.

As high-frequency aggregation is costly, it implements an aggregation
method that is optimized for fast, short-interval averaging, and makes
the aggregation frequency adaptive, such that high-frequency updates
only happen while monitored stall events are actively occurring.

With these patches applied, Android can monitor for, and ward off,
mounting memory shortages before they cause problems for the user. For
example, using memory stall monitors in userspace low memory killer
daemon (lmkd) we can detect mounting pressure and kill less important
processes before device becomes visibly sluggish.

In our memory stress testing psi memory monitors produce roughly 10x
less false positives compared to vmpressure signals. Having ability to
specify multiple triggers for the same psi metric allows other parts of
Android framework to monitor memory state of the device and act
accordingly.

The new interface is straightforward. The user opens one of the
pressure files for writing and writes a trigger description into the
file descriptor that defines the stall state - some or full, and the
maximum stall time over a given window of time. E.g.:

/* Signal when stall time exceeds 100ms of a 1s window */
char trigger[] = "full 100000 1000000";
fd = open("/proc/pressure/memory");
write(fd, trigger, sizeof(trigger));
while (poll() >= 0) {
...
}
close(fd);

When the monitored stall state is entered, psi adapts its aggregation
frequency according to what the configured time window requires in order
to emit event signals in a timely fashion. Once the stalling subsides,
aggregation reverts back to normal.

The trigger is associated with the open file descriptor. To stop
monitoring, the user only needs to close the file descriptor and the
trigger is discarded.

Patches 1-4 prepare the psi code for polling support. Patch 5
implements the adaptive polling logic, the pressure growth detection
optimized for short intervals, and hooks up write() and poll() on the
pressure files.

The patches were developed in collaboration with Johannes Weiner.

This patch (of 5):

Kernfs has a standardized poll/notification mechanism for waking all
pollers on all fds when a filesystem node changes. To allow polling for
custom events, add a .poll callback that can override the default.

This is in preparation for pollable cgroup pressure files which have
per-fd trigger configurations.

Link: http://lkml.kernel.org/r/20190124211518.244221-2-surenb@google.com
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff 147e1a97 Tue Mar 05 16:45:45 MST 2019 Johannes Weiner <hannes@cmpxchg.org> fs: kernfs: add poll file operation

Patch series "psi: pressure stall monitors", v3.

Android is adopting psi to detect and remedy memory pressure that
results in stuttering and decreased responsiveness on mobile devices.

Psi gives us the stall information, but because we're dealing with
latencies in the millisecond range, periodically reading the pressure
files to detect stalls in a timely fashion is not feasible. Psi also
doesn't aggregate its averages at a high enough frequency right now.

This patch series extends the psi interface such that users can
configure sensitive latency thresholds and use poll() and friends to be
notified when these are breached.

As high-frequency aggregation is costly, it implements an aggregation
method that is optimized for fast, short-interval averaging, and makes
the aggregation frequency adaptive, such that high-frequency updates
only happen while monitored stall events are actively occurring.

With these patches applied, Android can monitor for, and ward off,
mounting memory shortages before they cause problems for the user. For
example, using memory stall monitors in userspace low memory killer
daemon (lmkd) we can detect mounting pressure and kill less important
processes before device becomes visibly sluggish.

In our memory stress testing psi memory monitors produce roughly 10x
less false positives compared to vmpressure signals. Having ability to
specify multiple triggers for the same psi metric allows other parts of
Android framework to monitor memory state of the device and act
accordingly.

The new interface is straightforward. The user opens one of the
pressure files for writing and writes a trigger description into the
file descriptor that defines the stall state - some or full, and the
maximum stall time over a given window of time. E.g.:

/* Signal when stall time exceeds 100ms of a 1s window */
char trigger[] = "full 100000 1000000";
fd = open("/proc/pressure/memory");
write(fd, trigger, sizeof(trigger));
while (poll() >= 0) {
...
}
close(fd);

When the monitored stall state is entered, psi adapts its aggregation
frequency according to what the configured time window requires in order
to emit event signals in a timely fashion. Once the stalling subsides,
aggregation reverts back to normal.

The trigger is associated with the open file descriptor. To stop
monitoring, the user only needs to close the file descriptor and the
trigger is discarded.

Patches 1-4 prepare the psi code for polling support. Patch 5
implements the adaptive polling logic, the pressure growth detection
optimized for short intervals, and hooks up write() and poll() on the
pressure files.

The patches were developed in collaboration with Johannes Weiner.

This patch (of 5):

Kernfs has a standardized poll/notification mechanism for waking all
pollers on all fds when a filesystem node changes. To allow polling for
custom events, add a .poll callback that can override the default.

This is in preparation for pollable cgroup pressure files which have
per-fd trigger configurations.

Link: http://lkml.kernel.org/r/20190124211518.244221-2-surenb@google.com
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
/linux-master/include/linux/
H A Dkernfs.hdiff 4207b556 Tue Jan 09 14:48:04 MST 2024 Tejun Heo <tj@kernel.org> kernfs: RCU protect kernfs_nodes and avoid kernfs_idr_lock in kernfs_find_and_get_node_by_id()

The BPF helper bpf_cgroup_from_id() calls kernfs_find_and_get_node_by_id()
which acquires kernfs_idr_lock, which is an non-raw non-IRQ-safe lock. This
can lead to deadlocks as bpf_cgroup_from_id() can be called from any BPF
programs including e.g. the ones that attach to functions which are holding
the scheduler rq lock.

Consider the following BPF program:

SEC("fentry/__set_cpus_allowed_ptr_locked")
int BPF_PROG(__set_cpus_allowed_ptr_locked, struct task_struct *p,
struct affinity_context *affn_ctx, struct rq *rq, struct rq_flags *rf)
{
struct cgroup *cgrp = bpf_cgroup_from_id(p->cgroups->dfl_cgrp->kn->id);

if (cgrp) {
bpf_printk("%d[%s] in %s", p->pid, p->comm, cgrp->kn->name);
bpf_cgroup_release(cgrp);
}
return 0;
}

__set_cpus_allowed_ptr_locked() is called with rq lock held and the above
BPF program calls bpf_cgroup_from_id() within leading to the following
lockdep warning:

=====================================================
WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
6.7.0-rc3-work-00053-g07124366a1d7-dirty #147 Not tainted
-----------------------------------------------------
repro/1620 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
ffffffff833b3688 (kernfs_idr_lock){+.+.}-{2:2}, at: kernfs_find_and_get_node_by_id+0x1e/0x70

and this task is already holding:
ffff888237ced698 (&rq->__lock){-.-.}-{2:2}, at: task_rq_lock+0x4e/0xf0
which would create a new lock dependency:
(&rq->__lock){-.-.}-{2:2} -> (kernfs_idr_lock){+.+.}-{2:2}
...
Possible interrupt unsafe locking scenario:

CPU0 CPU1
---- ----
lock(kernfs_idr_lock);
local_irq_disable();
lock(&rq->__lock);
lock(kernfs_idr_lock);
<Interrupt>
lock(&rq->__lock);

*** DEADLOCK ***
...
Call Trace:
dump_stack_lvl+0x55/0x70
dump_stack+0x10/0x20
__lock_acquire+0x781/0x2a40
lock_acquire+0xbf/0x1f0
_raw_spin_lock+0x2f/0x40
kernfs_find_and_get_node_by_id+0x1e/0x70
cgroup_get_from_id+0x21/0x240
bpf_cgroup_from_id+0xe/0x20
bpf_prog_98652316e9337a5a___set_cpus_allowed_ptr_locked+0x96/0x11a
bpf_trampoline_6442545632+0x4f/0x1000
__set_cpus_allowed_ptr_locked+0x5/0x5a0
sched_setaffinity+0x1b3/0x290
__x64_sys_sched_setaffinity+0x4f/0x60
do_syscall_64+0x40/0xe0
entry_SYSCALL_64_after_hwframe+0x46/0x4e

Let's fix it by protecting kernfs_node and kernfs_root with RCU and making
kernfs_find_and_get_node_by_id() acquire rcu_read_lock() instead of
kernfs_idr_lock.

This adds an rcu_head to kernfs_node making it larger by 16 bytes on 64bit.
Combined with the preceding rearrange patch, the net increase is 8 bytes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andrea Righi <andrea.righi@canonical.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20240109214828.252092-4-tj@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff 79038a99 Mon Jul 24 06:18:16 MDT 2023 Arnd Bergmann <arnd@arndb.de> kernfs: add stub helper for kernfs_generic_poll()

In some randconfig builds, kernfs ends up being disabled, so there is no prototype
for kernfs_generic_poll()

In file included from kernel/sched/build_utility.c:97:
kernel/sched/psi.c:1479:3: error: implicit declaration of function 'kernfs_generic_poll' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
kernfs_generic_poll(t->of, wait);
^

Add a stub helper for it, as we have it for other kernfs functions.

Fixes: aff037078ecae ("sched/psi: use kernfs polling functions for PSI trigger polling")
Fixes: 147e1a97c4a0b ("fs: kernfs: add poll file operation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lore.kernel.org/r/20230724121823.1357562-1-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff 147e1a97 Tue Mar 05 16:45:45 MST 2019 Johannes Weiner <hannes@cmpxchg.org> fs: kernfs: add poll file operation

Patch series "psi: pressure stall monitors", v3.

Android is adopting psi to detect and remedy memory pressure that
results in stuttering and decreased responsiveness on mobile devices.

Psi gives us the stall information, but because we're dealing with
latencies in the millisecond range, periodically reading the pressure
files to detect stalls in a timely fashion is not feasible. Psi also
doesn't aggregate its averages at a high enough frequency right now.

This patch series extends the psi interface such that users can
configure sensitive latency thresholds and use poll() and friends to be
notified when these are breached.

As high-frequency aggregation is costly, it implements an aggregation
method that is optimized for fast, short-interval averaging, and makes
the aggregation frequency adaptive, such that high-frequency updates
only happen while monitored stall events are actively occurring.

With these patches applied, Android can monitor for, and ward off,
mounting memory shortages before they cause problems for the user. For
example, using memory stall monitors in userspace low memory killer
daemon (lmkd) we can detect mounting pressure and kill less important
processes before device becomes visibly sluggish.

In our memory stress testing psi memory monitors produce roughly 10x
less false positives compared to vmpressure signals. Having ability to
specify multiple triggers for the same psi metric allows other parts of
Android framework to monitor memory state of the device and act
accordingly.

The new interface is straightforward. The user opens one of the
pressure files for writing and writes a trigger description into the
file descriptor that defines the stall state - some or full, and the
maximum stall time over a given window of time. E.g.:

/* Signal when stall time exceeds 100ms of a 1s window */
char trigger[] = "full 100000 1000000";
fd = open("/proc/pressure/memory");
write(fd, trigger, sizeof(trigger));
while (poll() >= 0) {
...
}
close(fd);

When the monitored stall state is entered, psi adapts its aggregation
frequency according to what the configured time window requires in order
to emit event signals in a timely fashion. Once the stalling subsides,
aggregation reverts back to normal.

The trigger is associated with the open file descriptor. To stop
monitoring, the user only needs to close the file descriptor and the
trigger is discarded.

Patches 1-4 prepare the psi code for polling support. Patch 5
implements the adaptive polling logic, the pressure growth detection
optimized for short intervals, and hooks up write() and poll() on the
pressure files.

The patches were developed in collaboration with Johannes Weiner.

This patch (of 5):

Kernfs has a standardized poll/notification mechanism for waking all
pollers on all fds when a filesystem node changes. To allow polling for
custom events, add a .poll callback that can override the default.

This is in preparation for pollable cgroup pressure files which have
per-fd trigger configurations.

Link: http://lkml.kernel.org/r/20190124211518.244221-2-surenb@google.com
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff 147e1a97 Tue Mar 05 16:45:45 MST 2019 Johannes Weiner <hannes@cmpxchg.org> fs: kernfs: add poll file operation

Patch series "psi: pressure stall monitors", v3.

Android is adopting psi to detect and remedy memory pressure that
results in stuttering and decreased responsiveness on mobile devices.

Psi gives us the stall information, but because we're dealing with
latencies in the millisecond range, periodically reading the pressure
files to detect stalls in a timely fashion is not feasible. Psi also
doesn't aggregate its averages at a high enough frequency right now.

This patch series extends the psi interface such that users can
configure sensitive latency thresholds and use poll() and friends to be
notified when these are breached.

As high-frequency aggregation is costly, it implements an aggregation
method that is optimized for fast, short-interval averaging, and makes
the aggregation frequency adaptive, such that high-frequency updates
only happen while monitored stall events are actively occurring.

With these patches applied, Android can monitor for, and ward off,
mounting memory shortages before they cause problems for the user. For
example, using memory stall monitors in userspace low memory killer
daemon (lmkd) we can detect mounting pressure and kill less important
processes before device becomes visibly sluggish.

In our memory stress testing psi memory monitors produce roughly 10x
less false positives compared to vmpressure signals. Having ability to
specify multiple triggers for the same psi metric allows other parts of
Android framework to monitor memory state of the device and act
accordingly.

The new interface is straightforward. The user opens one of the
pressure files for writing and writes a trigger description into the
file descriptor that defines the stall state - some or full, and the
maximum stall time over a given window of time. E.g.:

/* Signal when stall time exceeds 100ms of a 1s window */
char trigger[] = "full 100000 1000000";
fd = open("/proc/pressure/memory");
write(fd, trigger, sizeof(trigger));
while (poll() >= 0) {
...
}
close(fd);

When the monitored stall state is entered, psi adapts its aggregation
frequency according to what the configured time window requires in order
to emit event signals in a timely fashion. Once the stalling subsides,
aggregation reverts back to normal.

The trigger is associated with the open file descriptor. To stop
monitoring, the user only needs to close the file descriptor and the
trigger is discarded.

Patches 1-4 prepare the psi code for polling support. Patch 5
implements the adaptive polling logic, the pressure growth detection
optimized for short intervals, and hooks up write() and poll() on the
pressure files.

The patches were developed in collaboration with Johannes Weiner.

This patch (of 5):

Kernfs has a standardized poll/notification mechanism for waking all
pollers on all fds when a filesystem node changes. To allow polling for
custom events, add a .poll callback that can override the default.

This is in preparation for pollable cgroup pressure files which have
per-fd trigger configurations.

Link: http://lkml.kernel.org/r/20190124211518.244221-2-surenb@google.com
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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