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

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

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

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
  ...

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 <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://lore.kernel.org/20250916082906.77439-4-marco.crivellari@suse.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

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.

system_wq is a per-CPU worqueue, yet nothing in its name tells about that
CPU affinity constraint, which is very often not required by users.
Make it clear by adding a system_percpu_wq to all the fs subsystem.

The old wq will be kept for a few release cylces.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Marco Crivellari <marco.crivellari@suse.com>
Link: https://lore.kernel.org/20250916082906.77439-3-marco.crivellari@suse.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

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 <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

With 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

We need to maintain b_dirty list ordering to keep writeback happy so
instead of sorting inode into appropriate place just append it at the
end of the list and clobber dirtied_time_when. This may result in inode
writeback starting later after cgroup switch however cgroup switches are
rare so it shouldn't matter much. Since the cgroup had write access to
the inode, there are no practical concerns of the possible DoS issues.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

process_inode_switch_wbs_work() can be switching over 100 inodes to a
different cgroup. Since switching an inode requires counting all dirty &
under-writeback pages in the address space of each inode, this can take
a significant amount of time. Add a possibility to reschedule after
processing each inode to avoid softlockups.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

There can be multiple inode switch works that are trying to switch
inodes to / from the same wb. This can happen in particular if some
cgroup exits which owns many (thousands) inodes and we need to switch
them all. In this case several inode_switch_wbs_work_fn() instances will
be just spinning on the same wb->list_lock while only one of them makes
forward progress. This wastes CPU cycles and quickly leads to softlockup
reports and unusable system.

Instead of running several inode_switch_wbs_work_fn() instances in
parallel switching to the same wb and contending on wb->list_lock, run
just one work item per wb and manage a queue of isw items switching to
this wb.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>