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Subject[PATCH 4.19 85/86] dm integrity: fix a deadlock due to offloading to an incorrect workqueue
From: Mikulas Patocka <>

commit 53770f0ec5fd417429775ba006bc4abe14002335 upstream.

If we need to perform synchronous I/O in dm_integrity_map_continue(),
we must make sure that we are not in the map function - in order to
avoid the deadlock due to bio queuing in generic_make_request. To
avoid the deadlock, we offload the request to metadata_wq.

However, metadata_wq also processes metadata updates for write requests.
If there are too many requests that get offloaded to metadata_wq at the
beginning of dm_integrity_map_continue, the workqueue metadata_wq
becomes clogged and the system is incapable of processing any metadata

This causes a deadlock because all the requests that need to do metadata
updates wait for metadata_wq to proceed and metadata_wq waits inside
wait_and_add_new_range until some existing request releases its range
lock (which doesn't happen because the range lock is released after
metadata update).

In order to fix the deadlock, we create a new workqueue offload_wq and
offload requests to it - so that processing of offload_wq is independent
from processing of metadata_wq.

Fixes: 7eada909bfd7 ("dm: add integrity target")
Cc: # v4.12+
Reported-by: Heinz Mauelshagen <>
Tested-by: Heinz Mauelshagen <>
Signed-off-by: Heinz Mauelshagen <>
Signed-off-by: Mikulas Patocka <>
Signed-off-by: Mike Snitzer <>
Signed-off-by: Greg Kroah-Hartman <>

drivers/md/dm-integrity.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -198,6 +198,7 @@ struct dm_integrity_c {
struct list_head wait_list;
wait_queue_head_t endio_wait;
struct workqueue_struct *wait_wq;
+ struct workqueue_struct *offload_wq;

unsigned char commit_seq;
commit_id_t commit_ids[N_COMMIT_IDS];
@@ -1237,7 +1238,7 @@ static void dec_in_flight(struct dm_inte
dio->range.logical_sector += dio->range.n_sectors;
bio_advance(bio, dio->range.n_sectors << SECTOR_SHIFT);
INIT_WORK(&dio->work, integrity_bio_wait);
- queue_work(ic->wait_wq, &dio->work);
+ queue_work(ic->offload_wq, &dio->work);
do_endio_flush(ic, dio);
@@ -1657,7 +1658,7 @@ static void dm_integrity_map_continue(st

if (need_sync_io && from_map) {
INIT_WORK(&dio->work, integrity_bio_wait);
- queue_work(ic->metadata_wq, &dio->work);
+ queue_work(ic->offload_wq, &dio->work);

@@ -3308,6 +3309,14 @@ static int dm_integrity_ctr(struct dm_ta
goto bad;

+ ic->offload_wq = alloc_workqueue("dm-integrity-offload", WQ_MEM_RECLAIM,
+ if (!ic->offload_wq) {
+ ti->error = "Cannot allocate workqueue";
+ r = -ENOMEM;
+ goto bad;
+ }
ic->commit_wq = alloc_workqueue("dm-integrity-commit", WQ_MEM_RECLAIM, 1);
if (!ic->commit_wq) {
ti->error = "Cannot allocate workqueue";
@@ -3544,6 +3553,8 @@ static void dm_integrity_dtr(struct dm_t
if (ic->wait_wq)
+ if (ic->offload_wq)
+ destroy_workqueue(ic->offload_wq);
if (ic->commit_wq)
if (ic->writer_wq)

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