kernel/linux.git/fs/fs-writeback.c, branch v6.18.21

writeback: don't block sync for filesystems with no data integrity guarantees

2026-04-02T11:23:20+00:00

commit 76f9377cd2ab7a9220c25d33940d9ca20d368172 upstream. Add a SB_I_NO_DATA_INTEGRITY superblock flag for filesystems that cannot guarantee data persistence on sync (eg fuse). For superblocks with this flag set, sync kicks off writeback of dirty inodes but does not wait for the flusher threads to complete the writeback. This replaces the per-inode AS_NO_DATA_INTEGRITY mapping flag added in commit f9a49aa302a0 ("fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()"). The flag belongs at the superblock level because data integrity is a filesystem-wide property, not a per-inode one. Having this flag at the superblock level also allows us to skip having to iterate every dirty inode in wait_sb_inodes() only to skip each inode individually. Prior to this commit, mappings with no data integrity guarantees skipped waiting on writeback completion but still waited on the flusher threads to finish initiating the writeback. Waiting on the flusher threads is unnecessary. This commit kicks off writeback but does not wait on the flusher threads. This change properly addresses a recent report [1] for a suspend-to-RAM hang seen on fuse-overlayfs that was caused by waiting on the flusher threads to finish: Workqueue: pm_fs_sync pm_fs_sync_work_fn Call Trace: __schedule+0x457/0x1720 schedule+0x27/0xd0 wb_wait_for_completion+0x97/0xe0 sync_inodes_sb+0xf8/0x2e0 __iterate_supers+0xdc/0x160 ksys_sync+0x43/0xb0 pm_fs_sync_work_fn+0x17/0xa0 process_one_work+0x193/0x350 worker_thread+0x1a1/0x310 kthread+0xfc/0x240 ret_from_fork+0x243/0x280 ret_from_fork_asm+0x1a/0x30 On fuse this is problematic because there are paths that may cause the flusher thread to block (eg if systemd freezes the user session cgroups first, which freezes the fuse daemon, before invoking the kernel suspend. The kernel suspend triggers ->write_node() which on fuse issues a synchronous setattr request, which cannot be processed since the daemon is frozen. Or if the daemon is buggy and cannot properly complete writeback, initiating writeback on a dirty folio already under writeback leads to writeback_get_folio() -> folio_prepare_writeback() -> unconditional wait on writeback to finish, which will cause a hang). This commit restores fuse to its prior behavior before tmp folios were removed, where sync was essentially a no-op. [1] https://lore.kernel.org/linux-fsdevel/CAJnrk1a-asuvfrbKXbEwwDSctvemF+6zfhdnuzO65Pt8HsFSRw@mail.gmail.com/T/#m632c4648e9cafc4239299887109ebd880ac6c5c1 Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Reported-by: John Cc: stable@vger.kernel.org Signed-off-by: Joanne Koong Link: https://patch.msgid.link/20260320005145.2483161-2-joannelkoong@gmail.com Reviewed-by: Jan Kara Reviewed-by: David Hildenbrand (Arm) Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

writeback: fix 100% CPU usage when dirtytime_expire_interval is 0

2026-02-06T15:57:37+00:00

commit 543467d6fe97e27e22a26e367fda972dbefebbff upstream. When vm.dirtytime_expire_seconds is set to 0, wakeup_dirtytime_writeback() schedules delayed work with a delay of 0, causing immediate execution. The function then reschedules itself with 0 delay again, creating an infinite busy loop that causes 100% kworker CPU usage. Fix by: - Only scheduling delayed work in wakeup_dirtytime_writeback() when dirtytime_expire_interval is non-zero - Cancelling the delayed work in dirtytime_interval_handler() when the interval is set to 0 - Adding a guard in start_dirtytime_writeback() for defensive coding Tested by booting kernel in QEMU with virtme-ng: - Before fix: kworker CPU spikes to ~73% - After fix: CPU remains at normal levels - Setting interval back to non-zero correctly resumes writeback Fixes: a2f4870697a5 ("fs: make sure the timestamps for lazytime inodes eventually get written") Cc: stable@vger.kernel.org Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220227 Signed-off-by: Laveesh Bansal Link: https://patch.msgid.link/20260106145059.543282-2-laveeshb@laveeshbansal.com Reviewed-by: Jan Kara Signed-off-by: Christian Brauner Signed-off-by: Greg Kroah-Hartman

fs/writeback: skip AS_NO_DATA_INTEGRITY mappings in wait_sb_inodes()

2026-01-30T09:32:15+00:00

commit f9a49aa302a05e91ca01f69031cb79a0ea33031f upstream. Above the while() loop in wait_sb_inodes(), we document that we must wait for all pages under writeback for data integrity. Consequently, if a mapping, like fuse, traditionally does not have data integrity semantics, there is no need to wait at all; we can simply skip these inodes. This restores fuse back to prior behavior where syncs are no-ops. This fixes a user regression where if a system is running a faulty fuse server that does not reply to issued write requests, this causes wait_sb_inodes() to wait forever. Link: https://lkml.kernel.org/r/20260105211737.4105620-2-joannelkoong@gmail.com Fixes: 0c58a97f919c ("fuse: remove tmp folio for writebacks and internal rb tree") Signed-off-by: Joanne Koong Reported-by: Athul Krishna Reported-by: J. Neuschäfer Reviewed-by: Bernd Schubert Tested-by: J. Neuschäfer Cc: Alexander Viro Cc: Bernd Schubert Cc: Bonaccorso Salvatore Cc: Christian Brauner Cc: David Hildenbrand Cc: Jan Kara Cc: "Liam R. Howlett" Cc: Lorenzo Stoakes Cc: "Matthew Wilcox (Oracle)" Cc: Michal Hocko Cc: Mike Rapoport Cc: Miklos Szeredi Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

Merge tag 'vfs-6.18-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-09-29T18:34:40+00:00

Pull vfs writeback updates from Christian Brauner: "This contains work adressing lockups reported by users when a systemd unit reading lots of files from a filesystem mounted with the lazytime mount option exits. With the lazytime mount option enabled we can be switching many dirty inodes on cgroup exit to the parent cgroup. The numbers observed in practice when systemd slice of a large cron job exits can easily reach hundreds of thousands or millions. The logic in inode_do_switch_wbs() which sorts the inode into appropriate place in b_dirty list of the target wb however has linear complexity in the number of dirty inodes thus overall time complexity of switching all the inodes is quadratic leading to workers being pegged for hours consuming 100% of the CPU and switching inodes to the parent wb. Simple reproducer of the issue: FILES=10000 # Filesystem mounted with lazytime mount option MNT=/mnt/ echo "Creating files and switching timestamps" for (( j = 0; j < 50; j ++ )); do mkdir $MNT/dir$j for (( i = 0; i < $FILES; i++ )); do echo "foo" >$MNT/dir$j/file$i done touch -a -t 202501010000 $MNT/dir$j/file* done wait echo "Syncing and flushing" sync echo 3 >/proc/sys/vm/drop_caches echo "Reading all files from a cgroup" mkdir /sys/fs/cgroup/unified/mycg1 || exit echo $$ >/sys/fs/cgroup/unified/mycg1/cgroup.procs || exit for (( j = 0; j < 50; j ++ )); do cat /mnt/dir$j/file* >/dev/null & done wait echo "Switching wbs" # Now rmdir the cgroup after the script exits This can be solved by: - Avoiding contention on the wb->list_lock when switching inodes by running a single work item per wb and managing a queue of items switching to the wb - Allowing rescheduling when switching inodes over to a different cgroup to avoid softlockups - Maintaining the b_dirty list ordering instead of sorting it" * tag 'vfs-6.18-rc1.writeback' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: writeback: Add tracepoint to track pending inode switches writeback: Avoid excessively long inode switching times writeback: Avoid softlockup when switching many inodes writeback: Avoid contention on wb->list_lock when switching inodes

Merge tag 'vfs-6.18-rc1.workqueue' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-09-29T17:27:17+00:00

Pull vfs workqueue updates from Christian Brauner: "This contains various workqueue changes affecting the filesystem layer. Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This replaces the use of system_wq and system_unbound_wq. system_wq is a per-CPU workqueue which isn't very obvious from the name and system_unbound_wq is to be used when locality is not required. So this renames system_wq to system_percpu_wq, and system_unbound_wq to system_dfl_wq. This also adds a new WQ_PERCPU flag to allow the fs subsystem users to explicitly request the use of per-CPU behavior. Both WQ_UNBOUND and WQ_PERCPU flags coexist for one release cycle to allow callers to transition their calls. WQ_UNBOUND will be removed in a next release cycle" * tag 'vfs-6.18-rc1.workqueue' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: fs: WQ_PERCPU added to alloc_workqueue users fs: replace use of system_wq with system_percpu_wq fs: replace use of system_unbound_wq with system_dfl_wq

Merge tag 'vfs-6.18-rc1.inode' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-09-29T16:42:30+00:00

Pull vfs inode updates from Christian Brauner: "This contains a series I originally wrote and that Eric brought over the finish line. It moves out the i_crypt_info and i_verity_info pointers out of 'struct inode' and into the fs-specific part of the inode. So now the few filesytems that actually make use of this pay the price in their own private inode storage instead of forcing it upon every user of struct inode. The pointer for the crypt and verity info is simply found by storing an offset to its address in struct fsverity_operations and struct fscrypt_operations. This shrinks struct inode by 16 bytes. I hope to move a lot more out of it in the future so that struct inode becomes really just about very core stuff that we need, much like struct dentry and struct file, instead of the dumping ground it has become over the years. On top of this are a various changes associated with the ongoing inode lifetime handling rework that multiple people are pushing forward: - Stop accessing inode->i_count directly in f2fs and gfs2. They simply should use the __iget() and iput() helpers - Make the i_state flags an enum - Rework the iput() logic Currently, if we are the last iput, and we have the I_DIRTY_TIME bit set, we will grab a reference on the inode again and then mark it dirty and then redo the put. This is to make sure we delay the time update for as long as possible We can rework this logic to simply dec i_count if it is not 1, and if it is do the time update while still holding the i_count reference Then we can replace the atomic_dec_and_lock with locking the ->i_lock and doing atomic_dec_and_test, since we did the atomic_add_unless above - Add an icount_read() helper and convert everyone that accesses inode->i_count directly for this purpose to use the helper - Expand dump_inode() to dump more information about an inode helping in debugging - Add some might_sleep() annotations to iput() and associated helpers" * tag 'vfs-6.18-rc1.inode' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: fs: add might_sleep() annotation to iput() and more fs: expand dump_inode() inode: fix whitespace issues fs: add an icount_read helper fs: rework iput logic fs: make the i_state flags an enum fs: stop accessing ->i_count directly in f2fs and gfs2 fsverity: check IS_VERITY() in fsverity_cleanup_inode() fs: remove inode::i_verity_info btrfs: move verity info pointer to fs-specific part of inode f2fs: move verity info pointer to fs-specific part of inode ext4: move verity info pointer to fs-specific part of inode fsverity: add support for info in fs-specific part of inode fs: remove inode::i_crypt_info ceph: move crypt info pointer to fs-specific part of inode ubifs: move crypt info pointer to fs-specific part of inode f2fs: move crypt info pointer to fs-specific part of inode ext4: move crypt info pointer to fs-specific part of inode fscrypt: add support for info in fs-specific part of inode fscrypt: replace raw loads of info pointer with helper function

Merge tag 'vfs-6.18-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2025-09-29T16:03:07+00:00

Pull misc vfs updates from Christian Brauner: "This contains the usual selections of misc updates for this cycle. Features: - Add "initramfs_options" parameter to set initramfs mount options. This allows to add specific mount options to the rootfs to e.g., limit the memory size - Add RWF_NOSIGNAL flag for pwritev2() Add RWF_NOSIGNAL flag for pwritev2. This flag prevents the SIGPIPE signal from being raised when writing on disconnected pipes or sockets. The flag is handled directly by the pipe filesystem and converted to the existing MSG_NOSIGNAL flag for sockets - Allow to pass pid namespace as procfs mount option Ever since the introduction of pid namespaces, procfs has had very implicit behaviour surrounding them (the pidns used by a procfs mount is auto-selected based on the mounting process's active pidns, and the pidns itself is basically hidden once the mount has been constructed) This implicit behaviour has historically meant that userspace was required to do some special dances in order to configure the pidns of a procfs mount as desired. Examples include: * In order to bypass the mnt_too_revealing() check, Kubernetes creates a procfs mount from an empty pidns so that user namespaced containers can be nested (without this, the nested containers would fail to mount procfs) But this requires forking off a helper process because you cannot just one-shot this using mount(2) * Container runtimes in general need to fork into a container before configuring its mounts, which can lead to security issues in the case of shared-pidns containers (a privileged process in the pidns can interact with your container runtime process) While SUID_DUMP_DISABLE and user namespaces make this less of an issue, the strict need for this due to a minor uAPI wart is kind of unfortunate Things would be much easier if there was a way for userspace to just specify the pidns they want. So this pull request contains changes to implement a new "pidns" argument which can be set using fsconfig(2): fsconfig(procfd, FSCONFIG_SET_FD, "pidns", NULL, nsfd); fsconfig(procfd, FSCONFIG_SET_STRING, "pidns", "/proc/self/ns/pid", 0); or classic mount(2) / mount(8): // mount -t proc -o pidns=/proc/self/ns/pid proc /tmp/proc mount("proc", "/tmp/proc", "proc", MS_..., "pidns=/proc/self/ns/pid"); Cleanups: - Remove the last references to EXPORT_OP_ASYNC_LOCK - Make file_remove_privs_flags() static - Remove redundant __GFP_NOWARN when GFP_NOWAIT is used - Use try_cmpxchg() in start_dir_add() - Use try_cmpxchg() in sb_init_done_wq() - Replace offsetof() with struct_size() in ioctl_file_dedupe_range() - Remove vfs_ioctl() export - Replace rwlock() with spinlock in epoll code as rwlock causes priority inversion on preempt rt kernels - Make ns_entries in fs/proc/namespaces const - Use a switch() statement() in init_special_inode() just like we do in may_open() - Use struct_size() in dir_add() in the initramfs code - Use str_plural() in rd_load_image() - Replace strcpy() with strscpy() in find_link() - Rename generic_delete_inode() to inode_just_drop() and generic_drop_inode() to inode_generic_drop() - Remove unused arguments from fcntl_{g,s}et_rw_hint() Fixes: - Document @name parameter for name_contains_dotdot() helper - Fix spelling mistake - Always return zero from replace_fd() instead of the file descriptor number - Limit the size for copy_file_range() in compat mode to prevent a signed overflow - Fix debugfs mount options not being applied - Verify the inode mode when loading it from disk in minixfs - Verify the inode mode when loading it from disk in cramfs - Don't trigger automounts with RESOLVE_NO_XDEV If openat2() was called with RESOLVE_NO_XDEV it didn't traverse through automounts, but could still trigger them - Add FL_RECLAIM flag to show_fl_flags() macro so it appears in tracepoints - Fix unused variable warning in rd_load_image() on s390 - Make INITRAMFS_PRESERVE_MTIME depend on BLK_DEV_INITRD - Use ns_capable_noaudit() when determining net sysctl permissions - Don't call path_put() under namespace semaphore in listmount() and statmount()" * tag 'vfs-6.18-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (38 commits) fcntl: trim arguments listmount: don't call path_put() under namespace semaphore statmount: don't call path_put() under namespace semaphore pid: use ns_capable_noaudit() when determining net sysctl permissions fs: rename generic_delete_inode() and generic_drop_inode() init: INITRAMFS_PRESERVE_MTIME should depend on BLK_DEV_INITRD initramfs: Replace strcpy() with strscpy() in find_link() initrd: Use str_plural() in rd_load_image() initramfs: Use struct_size() helper to improve dir_add() initrd: Fix unused variable warning in rd_load_image() on s390 fs: use the switch statement in init_special_inode() fs/proc/namespaces: make ns_entries const filelock: add FL_RECLAIM to show_fl_flags() macro eventpoll: Replace rwlock with spinlock selftests/proc: add tests for new pidns APIs procfs: add "pidns" mount option pidns: move is-ancestor logic to helper openat2: don't trigger automounts with RESOLVE_NO_XDEV namei: move cross-device check to __traverse_mounts namei: remove LOOKUP_NO_XDEV check from handle_mounts ...

fs: WQ_PERCPU added to alloc_workqueue users

2025-09-19T14:15:07+00:00

Currently if a user enqueue a work item using schedule_delayed_work() the used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to schedule_work() that is using system_wq and queue_work(), that makes use again of WORK_CPU_UNBOUND. This lack of consistentcy cannot be addressed without refactoring the API. alloc_workqueue() treats all queues as per-CPU by default, while unbound workqueues must opt-in via WQ_UNBOUND. This default is suboptimal: most workloads benefit from unbound queues, allowing the scheduler to place worker threads where they’re needed and reducing noise when CPUs are isolated. This patch adds a new WQ_PERCPU flag to all the fs subsystem users to explicitly request the use of the per-CPU behavior. Both flags coexist for one release cycle to allow callers to transition their calls. Once migration is complete, WQ_UNBOUND can be removed and unbound will become the implicit default. With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND), any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND must now use WQ_PERCPU. All existing users have been updated accordingly. Suggested-by: Tejun Heo Signed-off-by: Marco Crivellari Link: https://lore.kernel.org/20250916082906.77439-4-marco.crivellari@suse.com Signed-off-by: Christian Brauner

fs: replace use of system_wq with system_percpu_wq

2025-09-19T14:15:07+00:00

writeback: Add tracepoint to track pending inode switches

2025-09-19T11:11:06+00:00

Add trace_inode_switch_wbs_queue tracepoint to allow insight into how many inodes are queued to switch their bdi_writeback structure. Acked-by: Tejun Heo Signed-off-by: Jan Kara Signed-off-by: Christian Brauner