From e4f66341779d0cf4c83c74793753a84094286d9e Mon Sep 17 00:00:00 2001 From: Ming-Hung Tsai Date: Mon, 9 Feb 2026 15:54:09 +0800 Subject: [PATCH] dm cache: fix concurrent write failure in passthrough mode 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 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 Fixes: b29d4986d0da ("dm cache: significant rework to leverage dm-bio-prison-v2") Signed-off-by: Ming-Hung Tsai Signed-off-by: Mikulas Patocka --- 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 d3ef88b859ab..32d22c7b9a07 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; }