[PATCH v1 0/5] exfat: fix valid_size handling and locking

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

valid_size marks the on-disk up-to-date region of an exFAT file. It is
advanced from the write path, from read/zeroing completion, and via
truncate, while it is read without i_rwsem from ->iomap_begin and from bio
completion context. This series fixes several races and stale-data windows
that follow from that split ownership.

Patches 1-2 are self-contained fixes: an append write may be moved to EOF
by generic_write_checks(), so valid_size must be advanced using the
recalculated position; and exfat_zero_new_range() must mark non-uptodate
pages dirty so the whole page is written back.

Patches 3-4 are prerequisites for patch 5: truncate now holds the
invalidate lock so it is mutually exclusive with mmap writes, and
valid_size/zeroed_size become atomic so they can be read safely outside
i_rwsem. Patch 5 then takes exfat_page_mkwrite() out from under i_rwsem,
since blocking on the inode lock under mmap_lock could deadlock and its
VM_FAULT_RETRY result is not honored, and advances valid_size under the
folio lock to keep the page cache and valid_size consistent.

Link: https://lore.kernel.org/exfat/10029d6f-13cc-4d17-a2f9-b093a8339dde@163.com/T/#t

Chi Zhiling (5):
  exfat: advance valid_size to EOF for append writes
  exfat: dirty all new pages when extending valid_size
  exfat: hold the invalidate lock while truncating
  exfat: make valid_size and zeroed_size atomic
  exfat: use folio lock to protect valid_size

 fs/exfat/exfat_fs.h |  60 ++++++++++++++-
 fs/exfat/file.c     | 183 ++++++++++++++++----------------------------
 fs/exfat/inode.c    |  16 ++--
 fs/exfat/iomap.c    |  36 ++++++---
 fs/exfat/iomap.h    |   1 +
 fs/exfat/namei.c    |   4 +-
 6 files changed, 160 insertions(+), 140 deletions(-)

-- 
2.53.0