Commit bd68d220 authored Feb 17, 2020 by Mikulas Patocka Committed by Greg Kroah-Hartman Mar 11, 2020

dm integrity: fix a deadlock due to offloading to an incorrect workqueue



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
updates.

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: 7eada909 ("dm: add integrity target")
Cc: stable@vger.kernel.org # v4.12+
Reported-by: Heinz Mauelshagen <heinzm@redhat.com>
Tested-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9e6eb187

drivers/md/dm-integrity.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -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_integrity_io *dio)
		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);
		return;
		}
		do_endio_flush(ic, dio);
		@@ -1657,7 +1658,7 @@ static void dm_integrity_map_continue(struct dm_integrity_io *dio, bool from_map

		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);
		return;
		}

		@@ -3308,6 +3309,14 @@ static int dm_integrity_ctr(struct dm_target ti, unsigned argc, char *argv)
		goto bad;
		}

		ic->offload_wq = alloc_workqueue("dm-integrity-offload", WQ_MEM_RECLAIM,
		METADATA_WORKQUEUE_MAX_ACTIVE);
		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_target *ti)
		destroy_workqueue(ic->metadata_wq);
		if (ic->wait_wq)
		destroy_workqueue(ic->wait_wq);
		if (ic->offload_wq)
		destroy_workqueue(ic->offload_wq);
		if (ic->commit_wq)
		destroy_workqueue(ic->commit_wq);
		if (ic->writer_wq)