Re: [PATCH 5/8] ext4: don't zeroout if we have inflight direct IOs

[sashiko-bot@kernel.org]

> When endio conversion of an unwritten extent fails (e.g. ENOSPC while
> trying to split the extent), ext4 falls back to zeroing out the unwritten
> portions of the extent and marking it as written. This is safe only when no
> other in-flight writes have valid data underneath other parts of the same
> unwritten extent, otherwise the zeroout would silently corrupt that data.
> 
> Commit ea96cb5c4ae3 ("ext4: don't split extent before submitting I/O")
> changed the dio path to submit I/O without pre-splitting extents, deferring
> the split to endio. This means multiple concurrent writes can share a
> single unwritten extent, and a failed split on one of them could zeroout
> data belonging to another.
> 
> Buffered IO fixes this by counting such IOs on unwritten extents in
> i_conv_pending_ios and decrementing them after conversion. However, due to
> the way dio iomap is designed, it is not very straightforward for the FS
> [ ... ]
> for all inflight dio, not just dio over unwritten extents) but it keeps the
> code simple.
> 
> Fixes: ea96cb5c4ae3 ("ext4: don't split extent before submitting I/O")
> Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261102-ext4-endio-zero-bug-v1-0-266d2bb9e6dc@linux.ibm.com?part=5