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: b29d4986d0da ("dm cache: significant rework to leverage
dm-bio-prison-v2")
Signed-off-by: Ming-Hung Tsai <[email protected]>
---
drivers/md/dm-cache-target.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 8b62fe69722d..eb9d738704d0 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -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;
}
--
2.49.0
