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dm: fix a bug in dm_accept_partial_bio

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dm-writecache doesn't work in pmem mode - mkfs.ext4 and the following
fsck.ext4 fail with data corruption reported.

The commit 7dd76d1fee ("dm: improve bio splitting and associated IO
accounting") introduced a latent bug in dm_accept_partial_bio - it set
tio->io->sectors = n_sectors;. This is incorrect, according to the
diagram in the source code at dm_accept_partial_bio, it should be the
size of regions 1+2, not the region 2 alone.

The latent bug become real bug with the commit 8b211aaccb ("dm: add two
stage requeue mechanism").

dm-writecache in pmem mode is the only target that actually advances bio
with bio_advance and then calls dm_accept_partial_bio (so, the region 1
is non-empty). All the other targets call dm_accept_partial_bio with
region 1 empty, so bug went unnoticed for so long.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Assisted-by: Claude:claude-opus-5
Cc: stable@vger.kernel.org
Fixes: 8b211aaccb ("dm: add two stage requeue mechanism")
This commit is contained in:
Mikulas Patocka 2026-09-30 21:35:31 +02:00
parent 99909b74fb
commit a279804752
1 changed files with 1 additions and 1 deletions
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2
drivers/md/dm.c
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@ -1350,7 +1350,7 @@ void dm_accept_partial_bio(struct bio *bio, unsigned int n_sectors)
* for accounting but it is being reduced so update accordingly.
*/
dm_io_set_flag(io, DM_IO_WAS_SPLIT);
io->sectors = n_sectors;
io->sectors = *tio->len_ptr;
io->sector_offset = bio_sectors(io->orig_bio);
}
EXPORT_SYMBOL_GPL(dm_accept_partial_bio);