[PATCH v2 0/5] 9p: Fix refcounting and improve readability in lookup

[Tyler Hicks]

v2:
- Simplified the first patch, by removing code cleanups, to reduce churn
  and minimize regression potential in stable trees
  + The resulting changes are *identical* to the v1 submission when
    patches 1, 2, and 3 are applied
- Added patches 4 and 5 which are additional, minor code cleanups
v1: https://lore.kernel.org/lkml/20220525182530.266068-1-tyhicks@xxxxxxxxxxxxxxxxxxx/

The primary motivation for this series is patch #1 which fixes a
refcounting issue in the path walking code of
v9fs_fid_lookup_with_uid(). Userspace can cause fids, which are created
for use during lookup, to not be clunked and make the mount unusable.

The remaining patches are code cleanups to improve readability. They're
not critical.

I tested v1 and v2 by running fstests against 9p inside of QEMU to
ensure that the results were the same as without my changes applied. I
also backported patch #1 of v2 to linux-5.15.y (v5.15.32) and ensured
that the 'fid not clunked' issue did not occur when running against the
Windows Subsystem for Linux (WSL) 9p server.

Tyler

Tyler Hicks (5):
  9p: Fix refcounting during full path walks for fid lookups
  9p: Track the root fid with its own variable during lookups
  9p: Make the path walk logic more clear about when cloning is required
  9p: Remove unnecessary variable for old fids while walking from
    d_parent
  9p: Fix minor typo in code comment

 fs/9p/fid.c | 50 ++++++++++++++++++++++----------------------------
 1 file changed, 22 insertions(+), 28 deletions(-)

-- 
2.25.1