[PATCH v2 0/3] fs: drain in-flight DIO before buffered write fallback

[Jiale Yao]

An asynchronous direct write can remain in flight after its submitting
thread releases the inode lock.  If another direct write falls back to
buffered I/O in the meantime, the buffered write can dirty page cache
before the first write completes post-I/O invalidation.  The invalidation
then finds dirty pages, emits a page cache invalidation failure warning,
and records -EIO in the mapping error sequence.  A later fsync() returns
-EIO.

Commit 15cdefd0c0522f9d5e12d947fa04f4c11649b699 ("ext4: drain
in-flight DIO before buffered write fallback") fixed this race in ext4.
The same ordering is missing from the buffered fallback paths in ext2,
NTFS, and exFAT.

This series adds inode_dio_wait() before each fallback dirties page cache.
Each patch fixes one filesystem and remains independently buildable.  The
NTFS patch also avoids entering the blocking fallback for IOCB_NOWAIT
requests: it returns -EAGAIN if DIO made no progress and preserves a
positive result after a partial direct write.

A reproducer using concurrent AIO direct writes and buffered fallback
triggered the following warning on all three filesystems and made a
subsequent fsync() return -EIO:

  Page cache invalidation failure on direct I/O.  Possible data corruption
  due to collision with buffered I/O!

Changes in v2:
- Handle IOCB_NOWAIT before the potentially blocking NTFS fallback,
  returning -EAGAIN before any bytes are written and preserving a positive
  short-write result otherwise, as requested in review.

Jiale Yao (3):
  ext2: drain in-flight DIO before buffered write fallback
  ntfs: drain in-flight DIO before buffered write fallback
  exfat: drain in-flight DIO before buffered write fallback

 fs/exfat/file.c |  6 ++++++
 fs/ext2/file.c  |  7 +++++++
 fs/ntfs/file.c  | 13 +++++++++++++
 3 files changed, 26 insertions(+)

-- 
2.34.1