Re: [PATCH 4/8] ext4: don't zeroout if we have inflight unwritten IOs in non buffered-iomap path

[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 dioread_nolock writeback (non buffered iomap) and 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.
> 
> Fix this for dioread_nolock non buffered iomap writeback by making sure the
> writeback path increments the i_conv_pending_ios counter when it encounters
> an unwritten io_end, and decrements it after all the io_end_vecs have been
> converted. The existing checks in zeroout paths then use this counter to
> suppress the zeroout fallback whenever there are other unwritten IOs
> pending conversion, preventing silent data corruption.
> 
> 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=4