Re: [PATCH v9 03/14] xfs: don't change the block map under a dirty folio

[sashiko-bot@kernel.org]

> With CONFIG_TRANSPARENT_HUGEPAGE=y, writeback on XFS can write in place
> to a shared block and corrupt the other file that shares it.
> 
> xfs_map_blocks() writes in place unless the COW fork has an extent for
> the block. write() and write faults reserve one before they dirty a
> folio over a shared block, so xfs_flush_unmap_range() writes back and
> truncates the range before a clone changes the block map. But the holder
> of a GUP write pin takes no filesystem lock, and the truncate keeps a
> large dirty folio that straddles the range:
> 
>     clone                         pin holder         writeback
>     =====                         ==========         =========
>     writes the range back
>                                   dirties the folio
>     truncate keeps the folio
>     maps a shared block under it
>                                   dirties it again
>                                                      finds no COW extent
>                                                      writes in place
>                                                      /* shared block */
> 
> The fix used here is to invalidate the range instead of truncating it,
> and to fail the call with -EINVAL if a dirty folio is left, before the
> block map changes.
> 
> Fixes: 6795801366da ("xfs: Support large folios")
> 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=3