dm rq: fix the starting and stopping of blk-mq queues

dm rq: fix the starting and stopping of blk-mq queues

Orabug: 25308141

[ Upstream commit 7d9595d848cdff5c7939f68eec39e0c5d36a1d67 ]

Improve dm_stop_queue() to cancel any requeue_work.  Also, have
dm_start_queue() and dm_stop_queue() clear/set the QUEUE_FLAG_STOPPED
for the blk-mq request_queue.

On suspend dm_stop_queue() handles stopping the blk-mq request_queue
BUT: even though the hw_queues are marked BLK_MQ_S_STOPPED at that point
there is still a race that is allowing block/blk-mq.c to call ->queue_rq
against a hctx that it really shouldn't.  Add a check to
dm_mq_queue_rq() that guards against this rarity (albeit _not_
race-free).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # must patch dm.c on < 4.8 kernels
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
(cherry picked from commit 655fe78746d0b9141fe763535fc16d6652665c13)
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>