[PATCH 0/2] cifs: follow-on fixes to time_last_write mechanism

This series addresses two correctness issues in commit e8a8d54c2d50
("cifs: prevent readdir from changing file size due to stale directory
metadata"), which introduced the time_last_write field to protect cached
file sizes from stale Windows Server directory enumeration metadata.

Patch 1 consolidates the time_last_write stamp into _cifsFileInfo_put().
The original commit scattered the stamp across cifs_close(),
smb2_deferred_work_close(), and three deferred-close drain functions in
misc.c.  This missed the case where background I/O holds the final file
reference after userspace close() returns -- the stamp was anchored to
the earlier userspace-close time rather than the actual server close,
allowing the protection window to expire before the handle was removed
from openFileList.  Moving the stamp into _cifsFileInfo_put() under
open_file_lock provides a single canonical location that covers all close
paths and uses the spinlock's store-release/load-acquire pairing with
is_inode_writable() for correct memory ordering.

Patch 2 fixes the stamp placement in the setattr/truncate paths.
cifs_file_set_size() calls cifs_setsize() on success, which calls
i_size_write() and updates i_size.  The subsequent check
attrs->ia_size != i_size_read() therefore always evaluates false after a
successful cifs_file_set_size(), making the stamp dead code -- the
truncate path was completely unprotected.  The fix moves the stamp to
before the RPC call, guarded by attrs->ia_size != i_size_read() to
exclude no-op same-size ftruncate(2) calls.  On failure the stamp is
left in place rather than restored: restoring a stale snapshot (prev_tlw)
could silently erase a concurrent _cifsFileInfo_put() close stamp if that
close arrived between the READ_ONCE and the smp_store_release.  readdir
is suppressed until the stamp expires; stat() is unaffected because
cifs_revalidate_dentry_attr() uses from_readdir=false, bypassing the
time_last_write check entirely and always returning an authoritative
QUERY_INFO result.

Frank Sorenson (2):
  cifs: consolidate time_last_write stamp into _cifsFileInfo_put()
  cifs: fix time_last_write stamp placement in setattr/truncate paths

 fs/smb/client/file.c  | 37 ++++++++++++++++---------------------
 fs/smb/client/inode.c | 26 ++++++++++++++++++++++----
 fs/smb/client/misc.c  | 51 ++++++---------------------------------------------
 3 files changed, 44 insertions(+), 70 deletions(-)

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2.55.0