Commit a8c32a5c authored Nov 06, 2012 by Jens Axboe

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>

parent eac7cc52

drivers/md/dm.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -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