Merge patch series "ovl: narrow regions protected by i_rw_sem"

NeilBrown <neil@brown.name> says:

This series of patches for overlayfs is primarily focussed on preparing
for some proposed changes to directory locking.  In the new scheme we
will lock individual dentries in a directory rather than the whole
directory.

ovl currently will sometimes lock a directory on the upper filesystem
and do a few different things while holding the lock.  This is
incompatible with the new scheme.

This series narrows the region of code protected by the directory lock,
taking it multiple times when necessary.  This theoretically open up the
possibilty of other changes happening on the upper filesytem between the
unlock and the lock.  To some extent the patches guard against that by
checking the dentries still have the expect parent after retaking the
lock.  In general, I think ovl would have trouble if upperfs were being
changed independantly, and I don't think the changes here increase the
problem in any important way.

After this series (with any needed changes) lands I will resubmit my
change to vfs_rmdir() behaviour to have it drop the lock on error.  ovl
will be much better positioned to handle that change.  It will come with
the new "lookup_and_lock" API that I am proposing.

* patches from https://lore.kernel.org/20250716004725.1206467-1-neil@brown.name: (21 commits)
  ovl: rename ovl_cleanup_unlocked() to ovl_cleanup()
  ovl: change ovl_create_real() to receive dentry parent
  ovl: narrow locking in ovl_check_rename_whiteout()
  ovl: narrow locking in ovl_whiteout()
  ovl: change ovl_cleanup_and_whiteout() to take rename lock as needed
  ovl: narrow locking on ovl_remove_and_whiteout()
  ovl: change ovl_workdir_cleanup() to take dir lock as needed.
  ovl: narrow locking in ovl_workdir_cleanup_recurse()
  ovl: narrow locking in ovl_indexdir_cleanup()
  ovl: narrow locking in ovl_workdir_create()
  ovl: narrow locking in ovl_cleanup_index()
  ovl: narrow locking in ovl_cleanup_whiteouts()
  ovl: narrow locking in ovl_rename()
  ovl: simplify gotos in ovl_rename()
  ovl: narrow locking in ovl_create_over_whiteout()
  ovl: narrow locking in ovl_clear_empty()
  ovl: narrow locking in ovl_create_upper()
  ovl: narrow the locked region in ovl_copy_up_workdir()
  ovl: Call ovl_create_temp() without lock held.
  ovl: change ovl_create_index() to take dir locks
  ...

Link: https://lore.kernel.org/20250716004725.1206467-1-neil@brown.name
Signed-off-by: Christian Brauner <brauner@kernel.org>