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H A D | file_table.c | diff 9d5b9475 Mon Nov 20 16:35:12 MST 2023 Joel Granados <j.granados@samsung.com> 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> diff 9c565035 Fri Nov 17 16:02:17 MST 2017 Yang Shi <yang.s@alibaba-inc.com> vfs: remove unused hardirq.h Preempt counter APIs have been split out, currently, hardirq.h just includes irq_enter/exit APIs which are not used by vfs at all. So, remove the unused hardirq.h. Signed-off-by: Yang Shi <yang.s@alibaba-inc.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 9c225f26 Mon Mar 03 10:36:58 MST 2014 Linus Torvalds <torvalds@linux-foundation.org> vfs: atomic f_pos accesses as per POSIX Our write() system call has always been atomic in the sense that you get the expected thread-safe contiguous write, but we haven't actually guaranteed that concurrent writes are serialized wrt f_pos accesses, so threads (or processes) that share a file descriptor and use "write()" concurrently would quite likely overwrite each others data. This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says: "2.9.7 Thread Interactions with Regular File Operations All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: [...]" and one of the effects is the file position update. This unprotected file position behavior is not new behavior, and nobody has ever cared. Until now. Yongzhi Pan reported unexpected behavior to Michael Kerrisk that was due to this. This resolves the issue with a f_pos-specific lock that is taken by read/write/lseek on file descriptors that may be shared across threads or processes. Reported-by: Yongzhi Pan <panyongzhi@gmail.com> Reported-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 9c225f26 Mon Mar 03 10:36:58 MST 2014 Linus Torvalds <torvalds@linux-foundation.org> vfs: atomic f_pos accesses as per POSIX Our write() system call has always been atomic in the sense that you get the expected thread-safe contiguous write, but we haven't actually guaranteed that concurrent writes are serialized wrt f_pos accesses, so threads (or processes) that share a file descriptor and use "write()" concurrently would quite likely overwrite each others data. This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says: "2.9.7 Thread Interactions with Regular File Operations All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: [...]" and one of the effects is the file position update. This unprotected file position behavior is not new behavior, and nobody has ever cared. Until now. Yongzhi Pan reported unexpected behavior to Michael Kerrisk that was due to this. This resolves the issue with a f_pos-specific lock that is taken by read/write/lseek on file descriptors that may be shared across threads or processes. Reported-by: Yongzhi Pan <panyongzhi@gmail.com> Reported-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 9f3acc31 Thu Apr 24 05:44:08 MDT 2008 Al Viro <viro@zeniv.linux.org.uk> [PATCH] split linux/file.h Initial splitoff of the low-level stuff; taken to fdtable.h Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
H A D | namei.c | diff 9d5b9475 Mon Nov 20 16:35:12 MST 2023 Joel Granados <j.granados@samsung.com> 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> diff 9bc37e04 Wed Mar 15 16:34:34 MDT 2023 Al Viro <viro@zeniv.linux.org.uk> fs: introduce lock_rename_child() helper Pass the dentry of a source file and the dentry of a destination directory to lock parent inodes for rename. As soon as this function returns, ->d_parent of the source file dentry is stable and inodes are properly locked for calling vfs-rename. This helper is needed for ksmbd server. rename request of SMB protocol has to rename an opened file, no matter which directory it's in. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Namjae Jeon <linkinjeon@kernel.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff cac2f8b8 Thu Sep 22 09:17:00 MDT 2022 Christian Brauner <brauner@kernel.org> fs: rename current get acl method The current way of setting and getting posix acls through the generic xattr interface is error prone and type unsafe. The vfs needs to interpret and fixup posix acls before storing or reporting it to userspace. Various hacks exist to make this work. The code is hard to understand and difficult to maintain in it's current form. Instead of making this work by hacking posix acls through xattr handlers we are building a dedicated posix acl api around the get and set inode operations. This removes a lot of hackiness and makes the codepaths easier to maintain. A lot of background can be found in [1]. The current inode operation for getting posix acls takes an inode argument but various filesystems (e.g., 9p, cifs, overlayfs) need access to the dentry. In contrast to the ->set_acl() inode operation we cannot simply extend ->get_acl() to take a dentry argument. The ->get_acl() inode operation is called from: acl_permission_check() -> check_acl() -> get_acl() which is part of generic_permission() which in turn is part of inode_permission(). Both generic_permission() and inode_permission() are called in the ->permission() handler of various filesystems (e.g., overlayfs). So simply passing a dentry argument to ->get_acl() would amount to also having to pass a dentry argument to ->permission(). We should avoid this unnecessary change. So instead of extending the existing inode operation rename it from ->get_acl() to ->get_inode_acl() and add a ->get_acl() method later that passes a dentry argument and which filesystems that need access to the dentry can implement instead of ->get_inode_acl(). Filesystems like cifs which allow setting and getting posix acls but not using them for permission checking during lookup can simply not implement ->get_inode_acl(). This is intended to be a non-functional change. Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Suggested-by/Inspired-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> diff 1639a49c Thu Jul 14 00:11:27 MDT 2022 Yang Xu <xuyang2018.jy@fujitsu.com> fs: move S_ISGID stripping into the vfs_*() helpers Move setgid handling out of individual filesystems and into the VFS itself to stop the proliferation of setgid inheritance bugs. Creating files that have both the S_IXGRP and S_ISGID bit raised in directories that themselves have the S_ISGID bit set requires additional privileges to avoid security issues. When a filesystem creates a new inode it needs to take care that the caller is either in the group of the newly created inode or they have CAP_FSETID in their current user namespace and are privileged over the parent directory of the new inode. If any of these two conditions is true then the S_ISGID bit can be raised for an S_IXGRP file and if not it needs to be stripped. However, there are several key issues with the current implementation: * S_ISGID stripping logic is entangled with umask stripping. If a filesystem doesn't support or enable POSIX ACLs then umask stripping is done directly in the vfs before calling into the filesystem. If the filesystem does support POSIX ACLs then unmask stripping may be done in the filesystem itself when calling posix_acl_create(). Since umask stripping has an effect on S_ISGID inheritance, e.g., by stripping the S_IXGRP bit from the file to be created and all relevant filesystems have to call posix_acl_create() before inode_init_owner() where we currently take care of S_ISGID handling S_ISGID handling is order dependent. IOW, whether or not you get a setgid bit depends on POSIX ACLs and umask and in what order they are called. Note that technically filesystems are free to impose their own ordering between posix_acl_create() and inode_init_owner() meaning that there's additional ordering issues that influence S_SIGID inheritance. * Filesystems that don't rely on inode_init_owner() don't get S_ISGID stripping logic. While that may be intentional (e.g. network filesystems might just defer setgid stripping to a server) it is often just a security issue. This is not just ugly it's unsustainably messy especially since we do still have bugs in this area years after the initial round of setgid bugfixes. So the current state is quite messy and while we won't be able to make it completely clean as posix_acl_create() is still a filesystem specific call we can improve the S_SIGD stripping situation quite a bit by hoisting it out of inode_init_owner() and into the vfs creation operations. This means we alleviate the burden for filesystems to handle S_ISGID stripping correctly and can standardize the ordering between S_ISGID and umask stripping in the vfs. We add a new helper vfs_prepare_mode() so S_ISGID handling is now done in the VFS before umask handling. This has S_ISGID handling is unaffected unaffected by whether umask stripping is done by the VFS itself (if no POSIX ACLs are supported or enabled) or in the filesystem in posix_acl_create() (if POSIX ACLs are supported). The vfs_prepare_mode() helper is called directly in vfs_*() helpers that create new filesystem objects. We need to move them into there to make sure that filesystems like overlayfs hat have callchains like: sys_mknod() -> do_mknodat(mode) -> .mknod = ovl_mknod(mode) -> ovl_create(mode) -> vfs_mknod(mode) get S_ISGID stripping done when calling into lower filesystems via vfs_*() creation helpers. Moving vfs_prepare_mode() into e.g. vfs_mknod() takes care of that. This is in any case semantically cleaner because S_ISGID stripping is VFS security requirement. Security hooks so far have seen the mode with the umask applied but without S_ISGID handling done. The relevant hooks are called outside of vfs_*() creation helpers so by calling vfs_prepare_mode() from vfs_*() helpers the security hooks would now see the mode without umask stripping applied. For now we fix this by passing the mode with umask settings applied to not risk any regressions for LSM hooks. IOW, nothing changes for LSM hooks. It is worth pointing out that security hooks never saw the mode that is seen by the filesystem when actually creating the file. They have always been completely misplaced for that to work. The following filesystems use inode_init_owner() and thus relied on S_ISGID stripping: spufs, 9p, bfs, btrfs, ext2, ext4, f2fs, hfsplus, hugetlbfs, jfs, minix, nilfs2, ntfs3, ocfs2, omfs, overlayfs, ramfs, reiserfs, sysv, ubifs, udf, ufs, xfs, zonefs, bpf, tmpfs. All of the above filesystems end up calling inode_init_owner() when new filesystem objects are created through the ->mkdir(), ->mknod(), ->create(), ->tmpfile(), ->rename() inode operations. Since directories always inherit the S_ISGID bit with the exception of xfs when irix_sgid_inherit mode is turned on S_ISGID stripping doesn't apply. The ->symlink() and ->link() inode operations trivially inherit the mode from the target and the ->rename() inode operation inherits the mode from the source inode. All other creation inode operations will get S_ISGID handling via vfs_prepare_mode() when called from their relevant vfs_*() helpers. In addition to this there are filesystems which allow the creation of filesystem objects through ioctl()s or - in the case of spufs - circumventing the vfs in other ways. If filesystem objects are created through ioctl()s the vfs doesn't know about it and can't apply regular permission checking including S_ISGID logic. Therfore, a filesystem relying on S_ISGID stripping in inode_init_owner() in their ioctl() callpath will be affected by moving this logic into the vfs. We audited those filesystems: * btrfs allows the creation of filesystem objects through various ioctls(). Snapshot creation literally takes a snapshot and so the mode is fully preserved and S_ISGID stripping doesn't apply. Creating a new subvolum relies on inode_init_owner() in btrfs_new_subvol_inode() but only creates directories and doesn't raise S_ISGID. * ocfs2 has a peculiar implementation of reflinks. In contrast to e.g. xfs and btrfs FICLONE/FICLONERANGE ioctl() that is only concerned with the actual extents ocfs2 uses a separate ioctl() that also creates the target file. Iow, ocfs2 circumvents the vfs entirely here and did indeed rely on inode_init_owner() to strip the S_ISGID bit. This is the only place where a filesystem needs to call mode_strip_sgid() directly but this is self-inflicted pain. * spufs doesn't go through the vfs at all and doesn't use ioctl()s either. Instead it has a dedicated system call spufs_create() which allows the creation of filesystem objects. But spufs only creates directories and doesn't allo S_SIGID bits, i.e. it specifically only allows 0777 bits. * bpf uses vfs_mkobj() but also doesn't allow S_ISGID bits to be created. The patch will have an effect on ext2 when the EXT2_MOUNT_GRPID mount option is used, on ext4 when the EXT4_MOUNT_GRPID mount option is used, and on xfs when the XFS_FEAT_GRPID mount option is used. When any of these filesystems are mounted with their respective GRPID option then newly created files inherit the parent directories group unconditionally. In these cases non of the filesystems call inode_init_owner() and thus did never strip the S_ISGID bit for newly created files. Moving this logic into the VFS means that they now get the S_ISGID bit stripped. This is a user visible change. If this leads to regressions we will either need to figure out a better way or we need to revert. However, given the various setgid bugs that we found just in the last two years this is a regression risk we should take. Associated with this change is a new set of fstests to enforce the semantics for all new filesystems. Link: https://lore.kernel.org/ceph-devel/20220427092201.wvsdjbnc7b4dttaw@wittgenstein [1] Link: e014f37db1a2 ("xfs: use setattr_copy to set vfs inode attributes") [2] Link: 01ea173e103e ("xfs: fix up non-directory creation in SGID directories") [3] Link: fd84bfdddd16 ("ceph: fix up non-directory creation in SGID directories") [4] Link: https://lore.kernel.org/r/1657779088-2242-3-git-send-email-xuyang2018.jy@fujitsu.com Suggested-by: Dave Chinner <david@fromorbit.com> Suggested-by: Christian Brauner (Microsoft) <brauner@kernel.org> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-and-Tested-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com> [<brauner@kernel.org>: rewrote commit message] Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> diff 9c011be1 Fri Jan 21 23:13:13 MST 2022 Luis Chamberlain <mcgrof@kernel.org> fs: move namei sysctls to its own file 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 namei's own sysctl knobs to its own file. Other than the move we also avoid initializing two static variables to 0 as this is not needed: * sysctl_protected_symlinks * sysctl_protected_hardlinks Link: https://lkml.kernel.org/r/20211129205548.605569-8-mcgrof@kernel.org Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Antti Palosaari <crope@iki.fi> Cc: Eric Biederman <ebiederm@xmission.com> Cc: Iurii Zaikin <yzaikin@google.com> Cc: "J. Bruce Fields" <bfields@fieldses.org> Cc: Jeff Layton <jlayton@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Lukas Middendorf <kernel@tuxforce.de> Cc: Stephen Kitt <steve@sk2.org> Cc: Xiaoming Ni <nixiaoming@huawei.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 51cc3a66 Thu Sep 02 15:53:57 MDT 2021 Hugh Dickins <hughd@google.com> fs, mm: fix race in unlinking swapfile We had a recurring situation in which admin procedures setting up swapfiles would race with test preparation clearing away swapfiles; and just occasionally that got stuck on a swapfile "(deleted)" which could never be swapped off. That is not supposed to be possible. 2.6.28 commit f9454548e17c ("don't unlink an active swapfile") admitted that it was leaving a race window open: now close it. may_delete() makes the IS_SWAPFILE check (amongst many others) before inode_lock has been taken on target: now repeat just that simple check in vfs_unlink() and vfs_rename(), after taking inode_lock. Which goes most of the way to fixing the race, but swapon() must also check after it acquires inode_lock, that the file just opened has not already been unlinked. Link: https://lkml.kernel.org/r/e17b91ad-a578-9a15-5e3-4989e0f999b5@google.com Fixes: f9454548e17c ("don't unlink an active swapfile") Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 45f30dab Thu Jul 08 00:34:44 MDT 2021 Dmitry Kadashev <dkadashev@gmail.com> namei: update do_*() helpers to return ints Update the following to return int rather than long, for uniformity with the rest of the do_* helpers in namei.c: * do_rmdir() * do_unlinkat() * do_mkdirat() * do_mknodat() * do_symlinkat() Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <christian.brauner@ubuntu.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/io-uring/20210514143202.dmzfcgz5hnauy7ze@wittgenstein/ Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Link: https://lore.kernel.org/r/20210708063447.3556403-9-dkadashev@gmail.com Signed-off-by: Jens Axboe <axboe@kernel.dk> diff 2111c3c0 Mon Feb 15 21:29:28 MST 2021 Randy Dunlap <rdunlap@infradead.org> namei: fix kernel-doc for struct renamedata and more Fix kernel-doc warnings in namei.c: ../fs/namei.c:1149: warning: Excess function parameter 'dir_mode' description in 'may_create_in_sticky' ../fs/namei.c:1149: warning: Excess function parameter 'dir_uid' description in 'may_create_in_sticky' ../fs/namei.c:3396: warning: Function parameter or member 'open_flag' not described in 'vfs_tmpfile' ../fs/namei.c:3396: warning: Excess function parameter 'open_flags' description in 'vfs_tmpfile' ../fs/namei.c:4460: warning: Function parameter or member 'rd' not described in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'old_mnt_userns' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'old_dir' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'old_dentry' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'new_mnt_userns' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'new_dir' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'new_dentry' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'delegated_inode' description in 'vfs_rename' ../fs/namei.c:4460: warning: Excess function parameter 'flags' description in 'vfs_rename' Link: https://lore.kernel.org/r/20210216042929.8931-3-rdunlap@infradead.org Fixes: 9fe61450972d ("namei: introduce struct renamedata") Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Cc: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> diff 9fe61450 Thu Jan 21 06:19:32 MST 2021 Christian Brauner <christian.brauner@ubuntu.com> namei: introduce struct renamedata In order to handle idmapped mounts we will extend the vfs rename helper to take two new arguments in follow up patches. Since this operations already takes a bunch of arguments add a simple struct renamedata and make the current helper use it before we extend it. Link: https://lore.kernel.org/r/20210121131959.646623-14-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> diff 9deed3eb Fri Jan 17 06:45:08 MST 2020 Al Viro <viro@zeniv.linux.org.uk> new helper: traverse_mounts() common guts of follow_down() and follow_managed() taken to a new helper - traverse_mounts(). The remnants of follow_managed() are folded into its sole remaining caller (handle_mounts()). Calling conventions of handle_mounts() slightly sanitized - instead of the weird "1 for success, -E... for failure" that used to be imposed by the calling conventions of walk_component() et.al. we can use the normal "0 for success, -E... for failure". Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
H A D | open.c | diff b27c82e1 Tue Jun 21 08:14:54 MDT 2022 Christian Brauner <brauner@kernel.org> attr: port attribute changes to new types Now that we introduced new infrastructure to increase the type safety for filesystems supporting idmapped mounts port the first part of the vfs over to them. This ports the attribute changes codepaths to rely on the new better helpers using a dedicated type. Before this change we used to take a shortcut and place the actual values that would be written to inode->i_{g,u}id into struct iattr. This had the advantage that we moved idmappings mostly out of the picture early on but it made reasoning about changes more difficult than it should be. The filesystem was never explicitly told that it dealt with an idmapped mount. The transition to the value that needed to be stored in inode->i_{g,u}id appeared way too early and increased the probability of bugs in various codepaths. We know place the same value in struct iattr no matter if this is an idmapped mount or not. The vfs will only deal with type safe vfs{g,u}id_t. This makes it massively safer to perform permission checks as the type will tell us what checks we need to perform and what helpers we need to use. Fileystems raising FS_ALLOW_IDMAP can't simply write ia_vfs{g,u}id to inode->i_{g,u}id since they are different types. Instead they need to use the dedicated vfs{g,u}id_to_k{g,u}id() helpers that map the vfs{g,u}id into the filesystem. The other nice effect is that filesystems like overlayfs don't need to care about idmappings explicitly anymore and can simply set up struct iattr accordingly directly. Link: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com [1] Link: https://lore.kernel.org/r/20220621141454.2914719-9-brauner@kernel.org Cc: Seth Forshee <sforshee@digitalocean.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Al Viro <viro@zeniv.linux.org.uk> CC: linux-fsdevel@vger.kernel.org Reviewed-by: Seth Forshee <sforshee@digitalocean.com> Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> diff 55fc0d91 Fri Nov 05 14:43:41 MDT 2021 Rongwei Wang <rongwei.wang@linux.alibaba.com> mm, thp: lock filemap when truncating page cache Patch series "fix two bugs for file THP". This patch (of 2): Transparent huge page has supported read-only non-shmem files. The file- backed THP is collapsed by khugepaged and truncated when written (for shared libraries). However, there is a race when multiple writers truncate the same page cache concurrently. In that case, subpage(s) of file THP can be revealed by find_get_entry in truncate_inode_pages_range, which will trigger PageTail BUG_ON in truncate_inode_page, as follows: page:000000009e420ff2 refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff pfn:0x50c3ff head:0000000075ff816d order:9 compound_mapcount:0 compound_pincount:0 flags: 0x37fffe0000010815(locked|uptodate|lru|arch_1|head) raw: 37fffe0000000000 fffffe0013108001 dead000000000122 dead000000000400 raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 head: 37fffe0000010815 fffffe001066bd48 ffff000404183c20 0000000000000000 head: 0000000000000600 0000000000000000 00000001ffffffff ffff000c0345a000 page dumped because: VM_BUG_ON_PAGE(PageTail(page)) ------------[ cut here ]------------ kernel BUG at mm/truncate.c:213! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: xfs(E) libcrc32c(E) rfkill(E) ... CPU: 14 PID: 11394 Comm: check_madvise_d Kdump: ... Hardware name: ECS, BIOS 0.0.0 02/06/2015 pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--) Call trace: truncate_inode_page+0x64/0x70 truncate_inode_pages_range+0x550/0x7e4 truncate_pagecache+0x58/0x80 do_dentry_open+0x1e4/0x3c0 vfs_open+0x38/0x44 do_open+0x1f0/0x310 path_openat+0x114/0x1dc do_filp_open+0x84/0x134 do_sys_openat2+0xbc/0x164 __arm64_sys_openat+0x74/0xc0 el0_svc_common.constprop.0+0x88/0x220 do_el0_svc+0x30/0xa0 el0_svc+0x20/0x30 el0_sync_handler+0x1a4/0x1b0 el0_sync+0x180/0x1c0 Code: aa0103e0 900061e1 910ec021 9400d300 (d4210000) This patch mainly to lock filemap when one enter truncate_pagecache(), avoiding truncating the same page cache concurrently. Link: https://lkml.kernel.org/r/20211025092134.18562-1-rongwei.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/20211025092134.18562-2-rongwei.wang@linux.alibaba.com Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs") Signed-off-by: Xu Yu <xuyu@linux.alibaba.com> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org> Tested-by: Song Liu <song@kernel.org> Cc: Collin Fijalkovich <cfijalkovich@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: William Kucharski <william.kucharski@oracle.com> Cc: Yang Shi <shy828301@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 9e96c8c0 Tue Jul 14 00:55:05 MDT 2020 Christoph Hellwig <hch@lst.de> fs: add a vfs_fchmod helper Add a helper for struct file based chmode operations. To be used by the initramfs code soon. Signed-off-by: Christoph Hellwig <hch@lst.de> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> diff 278a5fba Fri May 24 03:30:34 MDT 2019 Christian Brauner <christian.brauner@ubuntu.com> open: add close_range() This adds the close_range() syscall. It allows to efficiently close a range of file descriptors up to all file descriptors of a calling task. I was contacted by FreeBSD as they wanted to have the same close_range() syscall as we proposed here. We've coordinated this and in the meantime, Kyle was fast enough to merge close_range() into FreeBSD already in April: https://reviews.freebsd.org/D21627 https://svnweb.freebsd.org/base?view=revision&revision=359836 and the current plan is to backport close_range() to FreeBSD 12.2 (cf. [2]) once its merged in Linux too. Python is in the process of switching to close_range() on FreeBSD and they are waiting on us to merge this to switch on Linux as well: https://bugs.python.org/issue38061 The syscall came up in a recent discussion around the new mount API and making new file descriptor types cloexec by default. During this discussion, Al suggested the close_range() syscall (cf. [1]). Note, a syscall in this manner has been requested by various people over time. First, it helps to close all file descriptors of an exec()ing task. This can be done safely via (quoting Al's example from [1] verbatim): /* that exec is sensitive */ unshare(CLONE_FILES); /* we don't want anything past stderr here */ close_range(3, ~0U); execve(....); The code snippet above is one way of working around the problem that file descriptors are not cloexec by default. This is aggravated by the fact that we can't just switch them over without massively regressing userspace. For a whole class of programs having an in-kernel method of closing all file descriptors is very helpful (e.g. demons, service managers, programming language standard libraries, container managers etc.). (Please note, unshare(CLONE_FILES) should only be needed if the calling task is multi-threaded and shares the file descriptor table with another thread in which case two threads could race with one thread allocating file descriptors and the other one closing them via close_range(). For the general case close_range() before the execve() is sufficient.) Second, it allows userspace to avoid implementing closing all file descriptors by parsing through /proc/<pid>/fd/* and calling close() on each file descriptor. From looking at various large(ish) userspace code bases this or similar patterns are very common in: - service managers (cf. [4]) - libcs (cf. [6]) - container runtimes (cf. [5]) - programming language runtimes/standard libraries - Python (cf. [2]) - Rust (cf. [7], [8]) As Dmitry pointed out there's even a long-standing glibc bug about missing kernel support for this task (cf. [3]). In addition, the syscall will also work for tasks that do not have procfs mounted and on kernels that do not have procfs support compiled in. In such situations the only way to make sure that all file descriptors are closed is to call close() on each file descriptor up to UINT_MAX or RLIMIT_NOFILE, OPEN_MAX trickery (cf. comment [8] on Rust). The performance is striking. For good measure, comparing the following simple close_all_fds() userspace implementation that is essentially just glibc's version in [6]: static int close_all_fds(void) { int dir_fd; DIR *dir; struct dirent *direntp; dir = opendir("/proc/self/fd"); if (!dir) return -1; dir_fd = dirfd(dir); while ((direntp = readdir(dir))) { int fd; if (strcmp(direntp->d_name, ".") == 0) continue; if (strcmp(direntp->d_name, "..") == 0) continue; fd = atoi(direntp->d_name); if (fd == dir_fd || fd == 0 || fd == 1 || fd == 2) continue; close(fd); } closedir(dir); return 0; } to close_range() yields: 1. closing 4 open files: - close_all_fds(): ~280 us - close_range(): ~24 us 2. closing 1000 open files: - close_all_fds(): ~5000 us - close_range(): ~800 us close_range() is designed to allow for some flexibility. Specifically, it does not simply always close all open file descriptors of a task. Instead, callers can specify an upper bound. This is e.g. useful for scenarios where specific file descriptors are created with well-known numbers that are supposed to be excluded from getting closed. For extra paranoia close_range() comes with a flags argument. This can e.g. be used to implement extension. Once can imagine userspace wanting to stop at the first error instead of ignoring errors under certain circumstances. There might be other valid ideas in the future. In any case, a flag argument doesn't hurt and keeps us on the safe side. From an implementation side this is kept rather dumb. It saw some input from David and Jann but all nonsense is obviously my own! - Errors to close file descriptors are currently ignored. (Could be changed by setting a flag in the future if needed.) - __close_range() is a rather simplistic wrapper around __close_fd(). My reasoning behind this is based on the nature of how __close_fd() needs to release an fd. But maybe I misunderstood specifics: We take the files_lock and rcu-dereference the fdtable of the calling task, we find the entry in the fdtable, get the file and need to release files_lock before calling filp_close(). In the meantime the fdtable might have been altered so we can't just retake the spinlock and keep the old rcu-reference of the fdtable around. Instead we need to grab a fresh reference to the fdtable. If my reasoning is correct then there's really no point in fancyfying __close_range(): We just need to rcu-dereference the fdtable of the calling task once to cap the max_fd value correctly and then go on calling __close_fd() in a loop. /* References */ [1]: https://lore.kernel.org/lkml/20190516165021.GD17978@ZenIV.linux.org.uk/ [2]: https://github.com/python/cpython/blob/9e4f2f3a6b8ee995c365e86d976937c141d867f8/Modules/_posixsubprocess.c#L220 [3]: https://sourceware.org/bugzilla/show_bug.cgi?id=10353#c7 [4]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/fd-util.c#L217 [5]: https://github.com/lxc/lxc/blob/ddf4b77e11a4d08f09b7b9cd13e593f8c047edc5/src/lxc/start.c#L236 [6]: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/grantpt.c;h=2030e07fa6e652aac32c775b8c6e005844c3c4eb;hb=HEAD#l17 Note that this is an internal implementation that is not exported. Currently, libc seems to not provide an exported version of this because of missing kernel support to do this. Note, in a recent patch series Florian made grantpt() a nop thereby removing the code referenced here. [7]: https://github.com/rust-lang/rust/issues/12148 [8]: https://github.com/rust-lang/rust/blob/5f47c0613ed4eb46fca3633c1297364c09e5e451/src/libstd/sys/unix/process2.rs#L303-L308 Rust's solution is slightly different but is equally unperformant. Rust calls getdtablesize() which is a glibc library function that simply returns the current RLIMIT_NOFILE or OPEN_MAX values. Rust then goes on to call close() on each fd. That's obviously overkill for most tasks. Rarely, tasks - especially non-demons - hit RLIMIT_NOFILE or OPEN_MAX. Let's be nice and assume an unprivileged user with RLIMIT_NOFILE set to 1024. Even in this case, there's a very high chance that in the common case Rust is calling the close() syscall 1021 times pointlessly if the task just has 0, 1, and 2 open. Suggested-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Kyle Evans <self@kyle-evans.net> Cc: Jann Horn <jannh@google.com> Cc: David Howells <dhowells@redhat.com> Cc: Dmitry V. Levin <ldv@altlinux.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Florian Weimer <fweimer@redhat.com> Cc: linux-api@vger.kernel.org diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 9e79b132 Tue Jan 31 01:34:55 MST 2017 Amir Goldstein <amir73il@gmail.com> vfs: deny fallocate() on directory There was an obscure use case of fallocate of directory inode in the vfs helper with the comment: "Let individual file system decide if it supports preallocation for directories or not." But there is no in-tree file system that implements fallocate for directory operations. Deny an attempt to fallocate a directory with EISDIR error. This change is needed prior to converting sb_start_write() to file_start_write(), so freeze protection is correctly handled for cases of fallocate file and blockdev. Cc: linux-api@vger.kernel.org Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> diff 9a08c352 Wed Feb 17 17:49:38 MST 2016 James Bottomley <James.Bottomley@HansenPartnership.com> fs: add filp_clone_open API I need an API that allows me to obtain a clone of the current file pointer to pass in to an exec handler. I've labelled this as an internal API because I can't see how it would be useful outside of the fs subsystem. The use case will be a persistent binfmt_misc handler. Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Acked-by: Jan Kara <jack@suse.cz> diff 9bf39ab2 Fri Jun 19 02:29:13 MDT 2015 Miklos Szeredi <mszeredi@suse.cz> vfs: add file_path() helper Turn d_path(&file->f_path, ...); into file_path(file, ...); Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
H A D | read_write.c | diff 06bbaa6d Mon Sep 26 09:59:14 MDT 2022 Al Viro <viro@zeniv.linux.org.uk> [coredump] don't use __kernel_write() on kmap_local_page() passing kmap_local_page() result to __kernel_write() is unsafe - random ->write_iter() might (and 9p one does) get unhappy when passed ITER_KVEC with pointer that came from kmap_local_page(). Fix by providing a variant of __kernel_write() that takes an iov_iter from caller (__kernel_write() becomes a trivial wrapper) and adding dump_emit_page() that parallels dump_emit(), except that instead of __kernel_write() it uses __kernel_write_iter() with ITER_BVEC source. Fixes: 3159ed57792b "fs/coredump: use kmap_local_page()" Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff c51acdb7 Fri Dec 31 00:57:50 MST 2021 Tal Zussman <tz2294@columbia.edu> fs: Remove FIXME comment in generic_write_checks() This patch removes an unnecessary comment that had to do with block special files from `generic_write_checks()`. The comment, originally added in Linux v2.4.14.9, was to clarify that we only set `pos` to the file size when the file was opened with `O_APPEND` if the file wasn't a block special file. Prior to Linux v2.4, block special files had a different `write()` function which was unified into a generic `write()` function in Linux v2.4. This generic `write()` function called `generic_write_checks()`. For more details, see this earlier conversation: https://lore.kernel.org/linux-fsdevel/Yc4Czk5A+p5p2Y4W@mit.edu/ Currently, block special devices have their own `write_iter()` function and no longer share the same `generic_write_checks()`, therefore rendering the comment irrelevant. Signed-off-by: Tal Zussman <tz2294@columbia.edu> Co-authored-by: Xijiao Li <xl2950@columbia.edu> Co-authored-by: Hans Montero <hjm2133@columbia.edu> Suggested-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 90fb7027 Tue Sep 29 18:18:34 MDT 2020 Linus Torvalds <torvalds@linux-foundation.org> autofs: use __kernel_write() for the autofs pipe writing autofs got broken in some configurations by commit 13c164b1a186 ("autofs: switch to kernel_write") because there is now an extra LSM permission check done by security_file_permission() in rw_verify_area(). autofs is one if the few places that really does want the much more limited __kernel_write(), because the write is an internal kernel one that shouldn't do any user permission checks (it also doesn't need the file_start_write/file_end_write logic, since it's just a pipe). There are a couple of other cases like that - accounting, core dumping, and splice - but autofs stands out because it can be built as a module. As a result, we need to export this internal __kernel_write() function again. We really don't want any other module to use this, but we don't have a "EXPORT_SYMBOL_FOR_AUTOFS_ONLY()". But we can mark it GPL-only to at least approximate that "internal use only" for licensing. While in this area, make autofs pass in NULL for the file position pointer, since it's always a pipe, and we now use a NULL file pointer for streaming file descriptors (see file_ppos() and commit 438ab720c675: "vfs: pass ppos=NULL to .read()/.write() of FMODE_STREAM files") This effectively reverts commits 9db977522449 ("fs: unexport __kernel_write") and 13c164b1a186 ("autofs: switch to kernel_write"). Fixes: 13c164b1a186 ("autofs: switch to kernel_write") Reported-by: Ondrej Mosnacek <omosnace@redhat.com> Acked-by: Christoph Hellwig <hch@lst.de> Acked-by: Acked-by: Ian Kent <raven@themaw.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 9db97752 Wed May 13 00:47:17 MDT 2020 Christoph Hellwig <hch@lst.de> fs: unexport __kernel_write This is a very special interface that skips sb_writes protection, and not used by modules anymore. Signed-off-by: Christoph Hellwig <hch@lst.de> diff 9e62ccec Fri Mar 20 04:20:12 MDT 2020 Michal Suchanek <msuchanek@suse.de> powerpc: Add back __ARCH_WANT_SYS_LLSEEK macro This partially reverts commit caf6f9c8a326 ("asm-generic: Remove unneeded __ARCH_WANT_SYS_LLSEEK macro") When CONFIG_COMPAT is disabled on ppc64 the kernel does not build. There is resistance to both removing the llseek syscall from the 64bit syscall tables and building the llseek interface unconditionally. Signed-off-by: Michal Suchanek <msuchanek@suse.de> Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/lkml/20190828151552.GA16855@infradead.org/ Link: https://lore.kernel.org/lkml/20190829214319.498c7de2@naga/ Link: https://lore.kernel.org/r/dd4575c51e31766e87f7e7fa121d099ab78d3290.1584699455.git.msuchanek@suse.de diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 10dce8af Tue Mar 26 16:20:43 MDT 2019 Kirill Smelkov <kirr@nexedi.com> fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock Commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per POSIX") added locking for file.f_pos access and in particular made concurrent read and write not possible - now both those functions take f_pos lock for the whole run, and so if e.g. a read is blocked waiting for data, write will deadlock waiting for that read to complete. This caused regression for stream-like files where previously read and write could run simultaneously, but after that patch could not do so anymore. See e.g. commit 581d21a2d02a ("xenbus: fix deadlock on writes to /proc/xen/xenbus") which fixes such regression for particular case of /proc/xen/xenbus. The patch that added f_pos lock in 2014 did so to guarantee POSIX thread safety for read/write/lseek and added the locking to file descriptors of all regular files. In 2014 that thread-safety problem was not new as it was already discussed earlier in 2006. However even though 2006'th version of Linus's patch was adding f_pos locking "only for files that are marked seekable with FMODE_LSEEK (thus avoiding the stream-like objects like pipes and sockets)", the 2014 version - the one that actually made it into the tree as 9c225f2655e3 - is doing so irregardless of whether a file is seekable or not. See https://lore.kernel.org/lkml/53022DB1.4070805@gmail.com/ https://lwn.net/Articles/180387 https://lwn.net/Articles/180396 for historic context. The reason that it did so is, probably, that there are many files that are marked non-seekable, but e.g. their read implementation actually depends on knowing current position to correctly handle the read. Some examples: kernel/power/user.c snapshot_read fs/debugfs/file.c u32_array_read fs/fuse/control.c fuse_conn_waiting_read + ... drivers/hwmon/asus_atk0110.c atk_debugfs_ggrp_read arch/s390/hypfs/inode.c hypfs_read_iter ... Despite that, many nonseekable_open users implement read and write with pure stream semantics - they don't depend on passed ppos at all. And for those cases where read could wait for something inside, it creates a situation similar to xenbus - the write could be never made to go until read is done, and read is waiting for some, potentially external, event, for potentially unbounded time -> deadlock. Besides xenbus, there are 14 such places in the kernel that I've found with semantic patch (see below): drivers/xen/evtchn.c:667:8-24: ERROR: evtchn_fops: .read() can deadlock .write() drivers/isdn/capi/capi.c:963:8-24: ERROR: capi_fops: .read() can deadlock .write() drivers/input/evdev.c:527:1-17: ERROR: evdev_fops: .read() can deadlock .write() drivers/char/pcmcia/cm4000_cs.c:1685:7-23: ERROR: cm4000_fops: .read() can deadlock .write() net/rfkill/core.c:1146:8-24: ERROR: rfkill_fops: .read() can deadlock .write() drivers/s390/char/fs3270.c:488:1-17: ERROR: fs3270_fops: .read() can deadlock .write() drivers/usb/misc/ldusb.c:310:1-17: ERROR: ld_usb_fops: .read() can deadlock .write() drivers/hid/uhid.c:635:1-17: ERROR: uhid_fops: .read() can deadlock .write() net/batman-adv/icmp_socket.c:80:1-17: ERROR: batadv_fops: .read() can deadlock .write() drivers/media/rc/lirc_dev.c:198:1-17: ERROR: lirc_fops: .read() can deadlock .write() drivers/leds/uleds.c:77:1-17: ERROR: uleds_fops: .read() can deadlock .write() drivers/input/misc/uinput.c:400:1-17: ERROR: uinput_fops: .read() can deadlock .write() drivers/infiniband/core/user_mad.c:985:7-23: ERROR: umad_fops: .read() can deadlock .write() drivers/gnss/core.c:45:1-17: ERROR: gnss_fops: .read() can deadlock .write() In addition to the cases above another regression caused by f_pos locking is that now FUSE filesystems that implement open with FOPEN_NONSEEKABLE flag, can no longer implement bidirectional stream-like files - for the same reason as above e.g. read can deadlock write locking on file.f_pos in the kernel. FUSE's FOPEN_NONSEEKABLE was added in 2008 in a7c1b990f715 ("fuse: implement nonseekable open") to support OSSPD. OSSPD implements /dev/dsp in userspace with FOPEN_NONSEEKABLE flag, with corresponding read and write routines not depending on current position at all, and with both read and write being potentially blocking operations: See https://github.com/libfuse/osspd https://lwn.net/Articles/308445 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1406 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1438-L1477 https://github.com/libfuse/osspd/blob/14a9cff0/osspd.c#L1479-L1510 Corresponding libfuse example/test also describes FOPEN_NONSEEKABLE as "somewhat pipe-like files ..." with read handler not using offset. However that test implements only read without write and cannot exercise the deadlock scenario: https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L124-L131 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L146-L163 https://github.com/libfuse/libfuse/blob/fuse-3.4.2-3-ga1bff7d/example/poll.c#L209-L216 I've actually hit the read vs write deadlock for real while implementing my FUSE filesystem where there is /head/watch file, for which open creates separate bidirectional socket-like stream in between filesystem and its user with both read and write being later performed simultaneously. And there it is semantically not easy to split the stream into two separate read-only and write-only channels: https://lab.nexedi.com/kirr/wendelin.core/blob/f13aa600/wcfs/wcfs.go#L88-169 Let's fix this regression. The plan is: 1. We can't change nonseekable_open to include &~FMODE_ATOMIC_POS - doing so would break many in-kernel nonseekable_open users which actually use ppos in read/write handlers. 2. Add stream_open() to kernel to open stream-like non-seekable file descriptors. Read and write on such file descriptors would never use nor change ppos. And with that property on stream-like files read and write will be running without taking f_pos lock - i.e. read and write could be running simultaneously. 3. With semantic patch search and convert to stream_open all in-kernel nonseekable_open users for which read and write actually do not depend on ppos and where there is no other methods in file_operations which assume @offset access. 4. Add FOPEN_STREAM to fs/fuse/ and open in-kernel file-descriptors via steam_open if that bit is present in filesystem open reply. It was tempting to change fs/fuse/ open handler to use stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags, but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE, and in particular GVFS which actually uses offset in its read and write handlers https://codesearch.debian.net/search?q=-%3Enonseekable+%3D https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346 https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481 so if we would do such a change it will break a real user. 5. Add stream_open and FOPEN_STREAM handling to stable kernels starting from v3.14+ (the kernel where 9c225f2655 first appeared). This will allow to patch OSSPD and other FUSE filesystems that provide stream-like files to return FOPEN_STREAM | FOPEN_NONSEEKABLE in their open handler and this way avoid the deadlock on all kernel versions. This should work because fs/fuse/ ignores unknown open flags returned from a filesystem and so passing FOPEN_STREAM to a kernel that is not aware of this flag cannot hurt. In turn the kernel that is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE is sufficient to implement streams without read vs write deadlock. This patch adds stream_open, converts /proc/xen/xenbus to it and adds semantic patch to automatically locate in-kernel places that are either required to be converted due to read vs write deadlock, or that are just safe to be converted because read and write do not use ppos and there are no other funky methods in file_operations. Regarding semantic patch I've verified each generated change manually - that it is correct to convert - and each other nonseekable_open instance left - that it is either not correct to convert there, or that it is not converted due to current stream_open.cocci limitations. The script also does not convert files that should be valid to convert, but that currently have .llseek = noop_llseek or generic_file_llseek for unknown reason despite file being opened with nonseekable_open (e.g. drivers/input/mousedev.c) Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Yongzhi Pan <panyongzhi@gmail.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Juergen Gross <jgross@suse.com> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Tejun Heo <tj@kernel.org> Cc: Kirill Tkhai <ktkhai@virtuozzo.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Christoph Hellwig <hch@lst.de> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Julia Lawall <Julia.Lawall@lip6.fr> Cc: Nikolaus Rath <Nikolaus@rath.org> Cc: Han-Wen Nienhuys <hanwen@google.com> Signed-off-by: Kirill Smelkov <kirr@nexedi.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> diff 9aae2050 Mon Oct 29 17:41:01 MDT 2018 Darrick J. Wong <darrick.wong@oracle.com> vfs: skip zero-length dedupe requests Don't bother calling the filesystem for a zero-length dedupe request; we can return zero and exit. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Dave Chinner <david@fromorbit.com> diff 9a219bc7 Fri Apr 03 20:10:20 MDT 2015 Al Viro <viro@zeniv.linux.org.uk> kill do_sync_read/do_sync_write all remaining instances of aio_{read,write} (all 4 of them) have explicit ->read and ->write resp.; do_sync_read/do_sync_write is never called by __vfs_read/__vfs_write anymore and no other users had been left. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> |
/linux-master/include/linux/ | ||
H A D | file.h | diff 9c930054 Tue Aug 31 04:36:24 MDT 2021 Xie Yongji <xieyongji@bytedance.com> file: Export receive_fd() to modules Export receive_fd() so that some modules can use it to pass file descriptor between processes without missing any security stuffs. Signed-off-by: Xie Yongji <xieyongji@bytedance.com> Acked-by: Jason Wang <jasowang@redhat.com> Link: https://lore.kernel.org/r/20210831103634.33-4-xieyongji@bytedance.com Signed-off-by: Michael S. Tsirkin <mst@redhat.com> diff 9c225f26 Mon Mar 03 10:36:58 MST 2014 Linus Torvalds <torvalds@linux-foundation.org> vfs: atomic f_pos accesses as per POSIX Our write() system call has always been atomic in the sense that you get the expected thread-safe contiguous write, but we haven't actually guaranteed that concurrent writes are serialized wrt f_pos accesses, so threads (or processes) that share a file descriptor and use "write()" concurrently would quite likely overwrite each others data. This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says: "2.9.7 Thread Interactions with Regular File Operations All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: [...]" and one of the effects is the file position update. This unprotected file position behavior is not new behavior, and nobody has ever cared. Until now. Yongzhi Pan reported unexpected behavior to Michael Kerrisk that was due to this. This resolves the issue with a f_pos-specific lock that is taken by read/write/lseek on file descriptors that may be shared across threads or processes. Reported-by: Yongzhi Pan <panyongzhi@gmail.com> Reported-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 9c225f26 Mon Mar 03 10:36:58 MST 2014 Linus Torvalds <torvalds@linux-foundation.org> vfs: atomic f_pos accesses as per POSIX Our write() system call has always been atomic in the sense that you get the expected thread-safe contiguous write, but we haven't actually guaranteed that concurrent writes are serialized wrt f_pos accesses, so threads (or processes) that share a file descriptor and use "write()" concurrently would quite likely overwrite each others data. This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says: "2.9.7 Thread Interactions with Regular File Operations All of the following functions shall be atomic with respect to each other in the effects specified in POSIX.1-2008 when they operate on regular files or symbolic links: [...]" and one of the effects is the file position update. This unprotected file position behavior is not new behavior, and nobody has ever cared. Until now. Yongzhi Pan reported unexpected behavior to Michael Kerrisk that was due to this. This resolves the issue with a f_pos-specific lock that is taken by read/write/lseek on file descriptors that may be shared across threads or processes. Reported-by: Yongzhi Pan <panyongzhi@gmail.com> Reported-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 9f3acc31 Thu Apr 24 05:44:08 MDT 2008 Al Viro <viro@zeniv.linux.org.uk> [PATCH] split linux/file.h Initial splitoff of the low-level stuff; taken to fdtable.h Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> diff 95e861db Sun Nov 13 17:06:24 MST 2005 Eric Dumazet <dada1@cosmosbay.com> [PATCH] reorder struct files_struct The file_lock spinlock sits close to mostly read fields of 'struct files_struct' In SMP (and NUMA) environments, each time a thread wants to open or close a file, it has to acquire the spinlock, thus invalidating the cache line containing this spinlock on other CPUS. So other threads doing read()/write()/... calls that use RCU to access the file table are going to ask further memory (possibly NUMA) transactions to read again this memory line. Move the spinlock to another cache line, so that concurrent threads can share the cache line containing 'count' and 'fdt' fields. It's worth up to 9% on a microbenchmark using a 4-thread 2-package x86 machine. See http://marc.theaimsgroup.com/?l=linux-kernel&m=112680448713342&w=2 Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> |
H A D | fs.h | diff 61d4fb0b Tue Oct 24 16:14:37 MDT 2023 Christian Brauner <brauner@kernel.org> file, i915: fix file reference for mmap_singleton() Today we got a report at [1] for rcu stalls on the i915 testsuite in [2] due to the conversion of files to SLAB_TYPSSAFE_BY_RCU. Afaict, get_file_rcu() goes into an infinite loop trying to carefully verify that i915->gem.mmap_singleton hasn't changed - see the splat below. So I stared at this code to figure out what it actually does. It seems that the i915->gem.mmap_singleton pointer itself never had rcu semantics. The i915->gem.mmap_singleton is replaced in file->f_op->release::singleton_release(): static int singleton_release(struct inode *inode, struct file *file) { struct drm_i915_private *i915 = file->private_data; cmpxchg(&i915->gem.mmap_singleton, file, NULL); drm_dev_put(&i915->drm); return 0; } The cmpxchg() is ordered against a concurrent update of i915->gem.mmap_singleton from mmap_singleton(). IOW, when mmap_singleton() fails to get a reference on i915->gem.mmap_singleton: While mmap_singleton() does rcu_read_lock(); file = get_file_rcu(&i915->gem.mmap_singleton); rcu_read_unlock(); it allocates a new file via anon_inode_getfile() and does smp_store_mb(i915->gem.mmap_singleton, file); So, then what happens in the case of this bug is that at some point fput() is called and drops the file->f_count to zero leaving the pointer in i915->gem.mmap_singleton in tact. Now, there might be delays until file->f_op->release::singleton_release() is called and i915->gem.mmap_singleton is set to NULL. Say concurrently another task hits mmap_singleton() and does: rcu_read_lock(); file = get_file_rcu(&i915->gem.mmap_singleton); rcu_read_unlock(); When get_file_rcu() fails to get a reference via atomic_inc_not_zero() it will try the reload from i915->gem.mmap_singleton expecting it to be NULL, assuming it has comparable semantics as we expect in __fget_files_rcu(). But it hasn't so it reloads the same pointer again, trying the same atomic_inc_not_zero() again and doing so until file->f_op->release::singleton_release() of the old file has been called. So, in contrast to __fget_files_rcu() here we want to not retry when atomic_inc_not_zero() has failed. We only want to retry in case we managed to get a reference but the pointer did change on reload. <3> [511.395679] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: <3> [511.395716] rcu: Tasks blocked on level-1 rcu_node (CPUs 0-9): P6238 <3> [511.395934] rcu: (detected by 16, t=65002 jiffies, g=123977, q=439 ncpus=20) <6> [511.395944] task:i915_selftest state:R running task stack:10568 pid:6238 tgid:6238 ppid:1001 flags:0x00004002 <6> [511.395962] Call Trace: <6> [511.395966] <TASK> <6> [511.395974] ? __schedule+0x3a8/0xd70 <6> [511.395995] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20 <6> [511.396003] ? lockdep_hardirqs_on+0xc3/0x140 <6> [511.396013] ? asm_sysvec_apic_timer_interrupt+0x1a/0x20 <6> [511.396029] ? get_file_rcu+0x10/0x30 <6> [511.396039] ? get_file_rcu+0x10/0x30 <6> [511.396046] ? i915_gem_object_mmap+0xbc/0x450 [i915] <6> [511.396509] ? i915_gem_mmap+0x272/0x480 [i915] <6> [511.396903] ? mmap_region+0x253/0xb60 <6> [511.396925] ? do_mmap+0x334/0x5c0 <6> [511.396939] ? vm_mmap_pgoff+0x9f/0x1c0 <6> [511.396949] ? rcu_is_watching+0x11/0x50 <6> [511.396962] ? igt_mmap_offset+0xfc/0x110 [i915] <6> [511.397376] ? __igt_mmap+0xb3/0x570 [i915] <6> [511.397762] ? igt_mmap+0x11e/0x150 [i915] <6> [511.398139] ? __trace_bprintk+0x76/0x90 <6> [511.398156] ? __i915_subtests+0xbf/0x240 [i915] <6> [511.398586] ? __pfx___i915_live_setup+0x10/0x10 [i915] <6> [511.399001] ? __pfx___i915_live_teardown+0x10/0x10 [i915] <6> [511.399433] ? __run_selftests+0xbc/0x1a0 [i915] <6> [511.399875] ? i915_live_selftests+0x4b/0x90 [i915] <6> [511.400308] ? i915_pci_probe+0x106/0x200 [i915] <6> [511.400692] ? pci_device_probe+0x95/0x120 <6> [511.400704] ? really_probe+0x164/0x3c0 <6> [511.400715] ? __pfx___driver_attach+0x10/0x10 <6> [511.400722] ? __driver_probe_device+0x73/0x160 <6> [511.400731] ? driver_probe_device+0x19/0xa0 <6> [511.400741] ? __driver_attach+0xb6/0x180 <6> [511.400749] ? __pfx___driver_attach+0x10/0x10 <6> [511.400756] ? bus_for_each_dev+0x77/0xd0 <6> [511.400770] ? bus_add_driver+0x114/0x210 <6> [511.400781] ? driver_register+0x5b/0x110 <6> [511.400791] ? i915_init+0x23/0xc0 [i915] <6> [511.401153] ? __pfx_i915_init+0x10/0x10 [i915] <6> [511.401503] ? do_one_initcall+0x57/0x270 <6> [511.401515] ? rcu_is_watching+0x11/0x50 <6> [511.401521] ? kmalloc_trace+0xa3/0xb0 <6> [511.401532] ? do_init_module+0x5f/0x210 <6> [511.401544] ? load_module+0x1d00/0x1f60 <6> [511.401581] ? init_module_from_file+0x86/0xd0 <6> [511.401590] ? init_module_from_file+0x86/0xd0 <6> [511.401613] ? idempotent_init_module+0x17c/0x230 <6> [511.401639] ? __x64_sys_finit_module+0x56/0xb0 <6> [511.401650] ? do_syscall_64+0x3c/0x90 <6> [511.401659] ? entry_SYSCALL_64_after_hwframe+0x6e/0xd8 <6> [511.401684] </TASK> Link: [1]: https://lore.kernel.org/intel-gfx/SJ1PR11MB6129CB39EED831784C331BAFB9DEA@SJ1PR11MB6129.namprd11.prod.outlook.com Link: [2]: https://intel-gfx-ci.01.org/tree/linux-next/next-20231013/bat-dg2-11/igt@i915_selftest@live@mman.html#dmesg-warnings10963 Cc: Jann Horn <jannh@google.com>, Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20231025-formfrage-watscheln-84526cd3bd7d@brauner Signed-off-by: Christian Brauner <brauner@kernel.org> diff 2c18a63b Fri Aug 18 08:00:51 MDT 2023 Christian Brauner <brauner@kernel.org> super: wait until we passed kill super Recent rework moved block device closing out of sb->put_super() and into sb->kill_sb() to avoid deadlocks as s_umount is held in put_super() and blkdev_put() can end up taking s_umount again. That means we need to move the removal of the superblock from @fs_supers out of generic_shutdown_super() and into deactivate_locked_super() to ensure that concurrent mounters don't fail to open block devices that are still in use because blkdev_put() in sb->kill_sb() hasn't been called yet. We can now do this as we can make iterators through @fs_super and @super_blocks wait without holding s_umount. Concurrent mounts will wait until a dying superblock is fully dead so until sb->kill_sb() has been called and SB_DEAD been set. Concurrent iterators can already discard any SB_DYING superblock. Reviewed-by: Jan Kara <jack@suse.cz> Message-Id: <20230818-vfs-super-fixes-v3-v3-4-9f0b1876e46b@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org> diff 5e874914 Fri Aug 18 08:00:50 MDT 2023 Christian Brauner <brauner@kernel.org> super: wait for nascent superblocks Recent patches experiment with making it possible to allocate a new superblock before opening the relevant block device. Naturally this has intricate side-effects that we get to learn about while developing this. Superblock allocators such as sget{_fc}() return with s_umount of the new superblock held and lock ordering currently requires that block level locks such as bdev_lock and open_mutex rank above s_umount. Before aca740cecbe5 ("fs: open block device after superblock creation") ordering was guaranteed to be correct as block devices were opened prior to superblock allocation and thus s_umount wasn't held. But now s_umount must be dropped before opening block devices to avoid locking violations. This has consequences. The main one being that iterators over @super_blocks and @fs_supers that grab a temporary reference to the superblock can now also grab s_umount before the caller has managed to open block devices and called fill_super(). So whereas before such iterators or concurrent mounts would have simply slept on s_umount until SB_BORN was set or the superblock was discard due to initalization failure they can now needlessly spin through sget{_fc}(). If the caller is sleeping on bdev_lock or open_mutex one caller waiting on SB_BORN will always spin somewhere and potentially this can go on for quite a while. It should be possible to drop s_umount while allowing iterators to wait on a nascent superblock to either be born or discarded. This patch implements a wait_var_event() mechanism allowing iterators to sleep until they are woken when the superblock is born or discarded. This also allows us to avoid relooping through @fs_supers and @super_blocks if a superblock isn't yet born or dying. Link: aca740cecbe5 ("fs: open block device after superblock creation") Reviewed-by: Jan Kara <jack@suse.cz> Message-Id: <20230818-vfs-super-fixes-v3-v3-3-9f0b1876e46b@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org> diff ffb6cf19 Mon Aug 07 13:38:40 MDT 2023 Jeff Layton <jlayton@kernel.org> fs: add infrastructure for multigrain timestamps The VFS always uses coarse-grained timestamps when updating the ctime and mtime after a change. This has the benefit of allowing filesystems to optimize away a lot metadata updates, down to around 1 per jiffy, even when a file is under heavy writes. Unfortunately, this has always been an issue when we're exporting via NFSv3, which relies on timestamps to validate caches. A lot of changes can happen in a jiffy, so timestamps aren't sufficient to help the client decide to invalidate the cache. Even with NFSv4, a lot of exported filesystems don't properly support a change attribute and are subject to the same problems with timestamp granularity. Other applications have similar issues with timestamps (e.g backup applications). If we were to always use fine-grained timestamps, that would improve the situation, but that becomes rather expensive, as the underlying filesystem would have to log a lot more metadata updates. What we need is a way to only use fine-grained timestamps when they are being actively queried. POSIX generally mandates that when the the mtime changes, the ctime must also change. The kernel always stores normalized ctime values, so only the first 30 bits of the tv_nsec field are ever used. Use the 31st bit of the ctime tv_nsec field to indicate that something has queried the inode for the mtime or ctime. When this flag is set, on the next mtime or ctime update, the kernel will fetch a fine-grained timestamp instead of the usual coarse-grained one. Filesytems can opt into this behavior by setting the FS_MGTIME flag in the fstype. Filesystems that don't set this flag will continue to use coarse-grained timestamps. Later patches will convert individual filesystems to use the new infrastructure. Signed-off-by: Jeff Layton <jlayton@kernel.org> Reviewed-by: Jan Kara <jack@suse.cz> Message-Id: <20230807-mgctime-v7-9-d1dec143a704@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org> diff 9cf3516c Sat Jul 08 09:55:27 MDT 2023 Jens Axboe <axboe@kernel.dk> fs: add IOCB flags related to passing back dio completions Async dio completions generally happen from hard/soft IRQ context, which means that users like iomap may need to defer some of the completion handling to a workqueue. This is less efficient than having the original issuer handle it, like we do for sync IO, and it adds latency to the completions. Add IOCB_DIO_CALLER_COMP, which the issuer can set if it is able to safely punt these completions to a safe context. If the dio handler is aware of this flag, assign a callback handler in kiocb->dio_complete and associated data io kiocb->private. The issuer will then call this handler with that data from task context. No functional changes in this patch. Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> diff 9b6304c1 Wed Jul 05 12:58:10 MDT 2023 Jeff Layton <jlayton@kernel.org> fs: add ctime accessors infrastructure struct timespec64 has unused bits in the tv_nsec field that can be used for other purposes. In future patches, we're going to change how the inode->i_ctime is accessed in certain inodes in order to make use of them. In order to do that safely though, we'll need to eradicate raw accesses of the inode->i_ctime field from the kernel. Add new accessor functions for the ctime that we use to replace them. Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Luis Chamberlain <mcgrof@kernel.org> Signed-off-by: Jeff Layton <jlayton@kernel.org> Reviewed-by: Damien Le Moal <dlemoal@kernel.org> Message-Id: <20230705185812.579118-2-jlayton@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org> diff 4f704d9a Mon Mar 13 17:51:10 MDT 2023 Christian Brauner <brauner@kernel.org> nfs: use vfs setgid helper We've aligned setgid behavior over multiple kernel releases. The details can be found in the following two merge messages: cf619f891971 ("Merge tag 'fs.ovl.setgid.v6.2') 426b4ca2d6a5 ("Merge tag 'fs.setgid.v6.0') Consistent setgid stripping behavior is now encapsulated in the setattr_should_drop_sgid() helper which is used by all filesystems that strip setgid bits outside of vfs proper. Switch nfs to rely on this helper as well. Without this patch the setgid stripping tests in xfstests will fail. Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Message-Id: <20230313-fs-nfs-setgid-v2-1-9a59f436cfc0@kernel.org> Signed-off-by: Christian Brauner <brauner@kernel.org> diff 17e81022 Fri Dec 30 14:52:52 MST 2022 Yu Zhao <yuzhao@google.com> mm: support POSIX_FADV_NOREUSE This patch adds POSIX_FADV_NOREUSE to vma_has_recency() so that the LRU algorithm can ignore access to mapped files marked by this flag. The advantages of POSIX_FADV_NOREUSE are: 1. Unlike MADV_SEQUENTIAL and MADV_RANDOM, it does not alter the default readahead behavior. 2. Unlike MADV_SEQUENTIAL and MADV_RANDOM, it does not split VMAs and therefore does not take mmap_lock. 3. Unlike MADV_COLD, setting it has a negligible cost, regardless of how many pages it affects. Its limitations are: 1. Like POSIX_FADV_RANDOM and POSIX_FADV_SEQUENTIAL, it currently does not support range. IOW, its scope is the entire file. 2. It currently does not ignore access through file descriptors. Specifically, for the active/inactive LRU, given a file page shared by two users and one of them having set POSIX_FADV_NOREUSE on the file, this page will be activated upon the second user accessing it. This corner case can be covered by checking POSIX_FADV_NOREUSE before calling folio_mark_accessed() on the read path. But it is considered not worth the effort. There have been a few attempts to support POSIX_FADV_NOREUSE, e.g., [1]. This time the goal is to fill a niche: a few desktop applications, e.g., large file transferring and video encoding/decoding, want fast file streaming with mmap() rather than direct IO. Among those applications, an SVT-AV1 regression was reported when running with MGLRU [2]. The following test can reproduce that regression. kb=$(awk '/MemTotal/ { print $2 }' /proc/meminfo) kb=$((kb - 8*1024*1024)) modprobe brd rd_nr=1 rd_size=$kb dd if=/dev/zero of=/dev/ram0 bs=1M mkfs.ext4 /dev/ram0 mount /dev/ram0 /mnt/ swapoff -a fallocate -l 8G /mnt/swapfile mkswap /mnt/swapfile swapon /mnt/swapfile wget http://ultravideo.cs.tut.fi/video/Bosphorus_3840x2160_120fps_420_8bit_YUV_Y4M.7z 7z e -o/mnt/ Bosphorus_3840x2160_120fps_420_8bit_YUV_Y4M.7z SvtAv1EncApp --preset 12 -w 3840 -h 2160 \ -i /mnt/Bosphorus_3840x2160.y4m For MGLRU, the following change showed a [9-11]% increase in FPS, which makes it on par with the active/inactive LRU. patch Source/App/EncApp/EbAppMain.c <<EOF 31a32 > #include <fcntl.h> 35d35 < #include <fcntl.h> /* _O_BINARY */ 117a118 > posix_fadvise(config->mmap.fd, 0, 0, POSIX_FADV_NOREUSE); EOF [1] https://lore.kernel.org/r/1308923350-7932-1-git-send-email-andrea@betterlinux.com/ [2] https://openbenchmarking.org/result/2209259-PTS-MGLRU8GB57 Link: https://lkml.kernel.org/r/20221230215252.2628425-2-yuzhao@google.com Signed-off-by: Yu Zhao <yuzhao@google.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andrea Righi <andrea.righi@canonical.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michael Larabel <Michael@MichaelLarabel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> diff 7420332a Thu Sep 22 09:17:01 MDT 2022 Christian Brauner <brauner@kernel.org> fs: add new get acl method The current way of setting and getting posix acls through the generic xattr interface is error prone and type unsafe. The vfs needs to interpret and fixup posix acls before storing or reporting it to userspace. Various hacks exist to make this work. The code is hard to understand and difficult to maintain in it's current form. Instead of making this work by hacking posix acls through xattr handlers we are building a dedicated posix acl api around the get and set inode operations. This removes a lot of hackiness and makes the codepaths easier to maintain. A lot of background can be found in [1]. Since some filesystem rely on the dentry being available to them when setting posix acls (e.g., 9p and cifs) they cannot rely on the old get acl inode operation to retrieve posix acl and need to implement their own custom handlers because of that. In a previous patch we renamed the old get acl inode operation to ->get_inode_acl(). We decided to rename it and implement a new one since ->get_inode_acl() is called generic_permission() and inode_permission() both of which can be called during an filesystem's ->permission() handler. So simply passing a dentry argument to ->get_acl() would have amounted to also having to pass a dentry argument to ->permission(). We avoided that change. This adds a new ->get_acl() inode operations which takes a dentry argument which filesystems such as 9p, cifs, and overlayfs can implement to get posix acls. Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> diff 7420332a Thu Sep 22 09:17:01 MDT 2022 Christian Brauner <brauner@kernel.org> fs: add new get acl method The current way of setting and getting posix acls through the generic xattr interface is error prone and type unsafe. The vfs needs to interpret and fixup posix acls before storing or reporting it to userspace. Various hacks exist to make this work. The code is hard to understand and difficult to maintain in it's current form. Instead of making this work by hacking posix acls through xattr handlers we are building a dedicated posix acl api around the get and set inode operations. This removes a lot of hackiness and makes the codepaths easier to maintain. A lot of background can be found in [1]. Since some filesystem rely on the dentry being available to them when setting posix acls (e.g., 9p and cifs) they cannot rely on the old get acl inode operation to retrieve posix acl and need to implement their own custom handlers because of that. In a previous patch we renamed the old get acl inode operation to ->get_inode_acl(). We decided to rename it and implement a new one since ->get_inode_acl() is called generic_permission() and inode_permission() both of which can be called during an filesystem's ->permission() handler. So simply passing a dentry argument to ->get_acl() would have amounted to also having to pass a dentry argument to ->permission(). We avoided that change. This adds a new ->get_acl() inode operations which takes a dentry argument which filesystems such as 9p, cifs, and overlayfs can implement to get posix acls. Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1] Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org> |
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