Re: [PATCH v9 07/14] xfs: test for reflink after the dio write checks

[sashiko-bot@kernel.org]

> A direct write that is not block aligned can expose stale disk contents
> on XFS if it races with the first clone of the file.
> 
> xfs_file_dio_write_unaligned() falls back to buffered I/O if the file is
> reflinked, and tests for that right after it takes the iolock. But
> xfs_file_write_checks() runs after the test and can drop the iolock, for
> example if S_NOSEC is not set. A clone can run in that gap:
> 
>     direct write                        clone
>     ============                        =====
>     takes the iolock shared
>     sees that the file is not reflinked
>     drops the iolock
>                                         shares the blocks
>     takes the iolock exclusive
>     writes a part of a new COW block
>     maps the whole block into the file
>       /* the rest was never written */
> 
> The fix used here is to move the test after xfs_file_write_checks().
> 
> Fixes: ed1128c2d0c8 ("xfs: reduce exclusive locking on unaligned dio")
> Signed-off-by: Chris Mason <mason@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112214604.67875-1-mason@kernel.org?part=7