Re: [PATCH v2 1/2] ext4: don't cache unzeroed blocks as written after a failed zeroout

[sashiko-bot@kernel.org]

> From: Daejun Park <daejun7.park@samsung.com>
> 
> ext4_ext_convert_to_initialized() may zero out the blocks before and
> after the range being written and convert them to written together with
> it, instead of splitting them off the unwritten extent. If
> ext4_ext_zeroout() fails for one side, it falls back to splitting the
> extent, so the blocks on that side stay unwritten in the extent tree.
> But zero_ex1 or zero_ex2 keeps its length, and ext4_zeroout_es() still
> inserts those blocks into the extent status tree as written.
> 
> Until that entry goes away, a read of those blocks returns whatever was
> on the disk before the extent was allocated. A write to them is mapped
> from the cache and goes in place without converting the extent, so its
> data would read back as zeroes once the entry is dropped. To reproduce
> on 4 KiB blocks with -o nodelalloc: fallocate 32 KiB, map the last seven
> blocks of that extent to dm-error, write the first block, restore the
> mapping and read the second block. It returns the old disk contents
> instead of zeroes.
> 
> Clear the length of an extent that could not be zeroed out, so that
> ext4_zeroout_es() skips it, as the comment at the out label intends.
> 
> Fixes: 308c57ccf431 ("ext4: if zeroout fails fall back to splitting the extent node")
> Cc: stable@vger.kernel.org
> Reviewed-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Daejun Park <daejun7.park@samsung.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261008-ext4-fc-zeroout-v2-0-55cab1e24fa3@samsung.com?part=1