Merge tag 'v6.5/vfs.rename.locking' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs rename locking updates from Christian Brauner:
 "This contains the work from Jan to fix problems with cross-directory
  renames originally reported in [1].

  To quickly sum it up some filesystems (so far we know at least about
  ext4, udf, f2fs, ocfs2, likely also reiserfs, gfs2 and others) need to
  lock the directory when it is being renamed into another directory.

  This is because we need to update the parent pointer in the directory
  in that case and if that races with other operations on the directory,
  in particular a conversion from one directory format into another, bad
  things can happen.

  So far we've done the locking in the filesystem code but recently
  Darrick pointed out in [2] that the RENAME_EXCHANGE case was missing.
  That one is particularly nasty because RENAME_EXCHANGE can arbitrarily
  mix regular files and directories and proper lock ordering is not
  achievable in the filesystems alone.

  This patch set adds locking into vfs_rename() so that not only parent
  directories but also moved inodes, regardless of whether they are
  directories or not, are locked when calling into the filesystem.

  This means establishing a locking order for unrelated directories. New
  helpers are added for this purpose and our documentation is updated to
  cover this in detail.

  The locking is now actually easier to follow as we now always lock
  source and target. We've always locked the target independent of
  whether it was a directory or file and we've always locked source if
  it was a regular file. The exact details for why this came about can
  be found in [3] and [4]"

Link: https://lore.kernel.org/all/20230117123735.un7wbamlbdihninm@quack3 [1]
Link: https://lore.kernel.org/all/20230517045836.GA11594@frogsfrogsfrogs [2]
Link: https://lore.kernel.org/all/20230526-schrebergarten-vortag-9cd89694517e@brauner [3]
Link: https://lore.kernel.org/all/20230530-seenotrettung-allrad-44f4b00139d4@brauner [4]

* tag 'v6.5/vfs.rename.locking' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: Restrict lock_two_nondirectories() to non-directory inodes
  fs: Lock moved directories
  fs: Establish locking order for unrelated directories
  Revert "f2fs: fix potential corruption when moving a directory"
  Revert "udf: Protect rename against modification of moved directory"
  ext4: Remove ext4 locking of moved directory

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