[PATCH v3 0/4] cifs: follow-on fixes after fscache_resize_cookie() consolidation

After commit fa724e235cfd ("cifs: add fscache_resize_cookie() to
cifs_setsize()") consolidated fscache cookie resizing into cifs_setsize(),
two further fixes are needed and two dead-code blocks became removable.

Patch 1 fixes cifs_do_truncate() (O_TRUNC via cifs_open()).  That path
runs without i_rwsem, so it cannot use the locked resize path.
cifs_invalidate_cache() is the correct alternative: it works without the
lock and ensures stale cached data is not served once the cookie is later
activated.

Patch 2 addresses a race identified during review: cifs_setsize() calls
fscache_resize_cookie() without i_rwsem, but another concurrent open may
already have the cookie active (IS_CACHING set), making fscache_resize_cookie()
a real operation requiring the lock.  The fix strips fscache_resize_cookie()
from cifs_setsize() and introduces cifs_resize_file_locked(), which
temporarily activates the cookie with fscache_use_cookie(), performs the
resize under i_rwsem, then deactivates it.  Callers that already hold
i_rwsem (cifs_file_set_size, smb2_duplicate_extents, smb3_simple_falloc)
switch to the wrapper; cifs_do_truncate() continues to use cifs_setsize()
followed by cifs_invalidate_cache() as established in patch 1.

Patches 3 and 4 remove dead code.  Patch 3 removes a caller-side
truncate_setsize() + fscache_resize_cookie() block from
cifs_remap_file_range() that became redundant once smb2_duplicate_extents()
started performing the full size update via cifs_setsize() under the
i_rwsem held by lock_two_nondirectories().  Patch 4 removes equivalent
dead blocks from cifs_setattr_unix() and cifs_setattr_nounix(): since
cifs_file_set_size() calls cifs_setsize() on success, i_size always equals
attrs->ia_size on the success path, making the subsequent size-inequality
blocks unreachable.

v3: Fixed broken patch
v2:
  - Added patch 2 (cifs_resize_file_locked): based on review feedback
    (Huiwen He) that the fscache cookie is not guaranteed to be quiescent
    in cifs_do_truncate() - another concurrent open may already have it
    active.  The fix strips fscache_resize_cookie() from cifs_setsize() and
    adds a locked wrapper for callers that hold i_rwsem.
  - Patch 1 commit message updated: the original rationale (cookie is
    always quiescent in cifs_do_truncate) was incorrect; the correct reason
    is that i_rwsem cannot be held in that path.
  - Patches 2-3 from v1 renumbered to 3-4 to place fixes before cleanups.
  - Patches 3-4: add Reviewed-by from Huiwen He; otherwise unchanged from v1.
  - All patches: add Reviewed-by from Paulo Alcantara.

Frank Sorenson (4):
  cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC
  cifs: add cifs_resize_file_locked() to guard fscache_resize_cookie()
    under i_rwsem
  cifs: remove redundant size-update block in cifs_remap_file_range()
  cifs: remove dead size-update blocks in cifs_setattr_unix/nounix

 fs/smb/client/cifsfs.c  |  6 +-----
 fs/smb/client/cifsfs.h  |  1 +
 fs/smb/client/file.c    |  1 +
 fs/smb/client/inode.c   | 41 ++++++++++++++++++++++-------------------
 fs/smb/client/smb2ops.c |  9 +++------
 5 files changed, 28 insertions(+), 30 deletions(-)

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2.55.0