dm: fix deadlock with request based dm and queue request_fn recursion

Request based dm attempts to re-run the request queue off the
request completion path. If used with a driver that potentially does
end_io from its request_fn, we could deadlock trying to recurse
back into request dispatch. Fix this by punting the request queue
run to kblockd.

Tested to fix a quickly reproducible deadlock in such a scenario.

Cc: stable@kernel.org
Acked-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 02db9183ca01..77e6eff41cae 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -740,8 +740,14 @@ static void rq_completed(struct mapped_device *md, int rw, int run_queue)
         if (!md_in_flight(md))
                 wake_up(&md->wait);
 
+        /*
+         * Run this off this callpath, as drivers could invoke end_io while
+         * inside their request_fn (and holding the queue lock). Calling
+         * back into ->request_fn() could deadlock attempting to grab the
+         * queue lock again.
+         */
         if (run_queue)
-                blk_run_queue(md->queue);
+                blk_run_queue_async(md->queue);
 
         /*
          * dm_put() must be at the end of this function. See the comment above