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dm cache: fix concurrent write failure in passthrough mode

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When bio prison cell lock acquisition fails due to concurrent writes to
the same block in passthrough mode, dm-cache incorrectly returns an I/O
error instead of properly handling the concurrency. This can occur in
both process and workqueue contexts when invalidate_lock() is called for
exclusive access to a data block. Fix this by deferring the write bios
to ensure proper block device behavior.

Reproduce steps:

1. Create a cache device

dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 131072 linear /dev/sdc 8192"
dmsetup create corig --table "0 262144 linear /dev/sdc 262144"
dd if=/dev/zero of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache --table "0 262144 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"

2. Promote the first data block into cache

fio --filename=/dev/mapper/cache --name=populate --rw=write --bs=4k \
--direct=1 --size=64k

3. Reload the cache into passthrough mode

dmsetup suspend cache
dmsetup reload cache --table "0 262144 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 passthrough smq 0"
dmsetup resume cache

4. Write to the first cached block concurrently. Sometimes one of the
   processes will receive I/O errors.

fio --filename=/dev/mapper/cache --name test --rw=randwrite --bs=4k \
--randrepeat=0 --direct=1 --numjobs=2 --size 64k

 <snip>
 fio-3.41
 fio: io_u error on file /dev/mapper/cache: Input/output error: write offset=4096, buflen=4096
 fio: pid=106, err=5/file:io_u.c:2008, func=io_u error, error=Input/output error
 test: (groupid=0, jobs=1): err= 0: pid=105
 test: (groupid=0, jobs=1): err= 5 (file:io_u.c:2008, func=io_u error, error=Input/output error): pid=106
 <snip>

Fixes: b29d4986d0 ("dm cache: significant rework to leverage dm-bio-prison-v2")
Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
This commit is contained in:
Ming-Hung Tsai 2026-02-09 15:54:09 +08:00 committed by Mikulas Patocka
parent 2d1f7b65f5
commit e4f6634177
1 changed files with 9 additions and 0 deletions
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9
drivers/md/dm-cache-target.c
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@ -1561,6 +1561,15 @@ static int invalidate_lock(struct dm_cache_migration *mg)
READ_WRITE_LOCK_LEVEL, prealloc, &mg->cell);
if (r < 0) {
free_prison_cell(cache, prealloc);
/* Defer the bio for retrying the cell lock */
if (mg->overwrite_bio) {
struct bio *bio = mg->overwrite_bio;
mg->overwrite_bio = NULL;
defer_bio(cache, bio);
}
invalidate_complete(mg, false);
return r;
}