Re: [PATCH v9 04/14] iomap: don't punch delalloc under a dirty EOF block

[sashiko-bot@kernel.org]

> After a failed buffered write, writeback on XFS can write in place to
> the shared block that contains EOF, and corrupt the other file that
> shares it.
> 
> After a failed buffered write, iomap_write_delalloc_release() punches
> the delalloc reservation of the write, except under dirty folios, which
> still need it. It looks for dirty folios only up to i_size, and punches
> the rest unconditionally. But XFS rounds that punch down to a block
> boundary, so the block that contains EOF loses its COW fork reservation,
> and writeback goes to the shared block:
> 
>     block size 4096, i_size 5000, reservation 4096 to 8192
>     searched for dirty folios:  4096 to 5000
>     punched unconditionally:    5000 to 8192
>     rounded to blocks by XFS:   4096 to 8192
> 
> The fix used here is to look for dirty folios up to the end of the block
> that contains EOF.
> 
> Fixes: f43dc4dc3eff ("iomap: buffered write failure should not truncate the page cache")
> Fixes: f6f91d290c8b ("xfs: punch delalloc extents from the COW fork for COW writes")
> 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=4