Re: [PATCH 3/4] ext4: don't put a DUN wraparound in the middle of a read bio

[sashiko-bot@kernel.org]

> Under IV_INO_LBLK_32, a file's DUNs wrap at 2^32, and the policy
> is only allowed when the block size equals the page size.
> 
> ext4_mpage_readpages() adds a whole folio to one bio, but checks
> only the DUN of the first block. blk-crypto assumes the DUNs
> in a bio are contiguous and never wraps them, so blocks past
> the wraparound are read with the wrong DUNs.
> 
> Writeback and direct I/O get this right, but with large folios
> a single folio can still span the wraparound.
> 
> Fix this by routing such a folio through the buffer_head path,
> which submits one bio per block and so gives each block its own DUN.
> 
> fscrypt_limit_io_blocks() tells whether the wraparound falls after
> the first block; a wraparound at the first block itself is already
> caught by fscrypt_mergeable_bio().
> 
> A file's DUNs wrap at most once, so at most one folio per file takes
> the slower path, and the per-block bios can be merged again by the
> block layer.
> 
> Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261103153132.4154855-1-libaokun@linux.alibaba.com?part=3