dm rq: don't queue request to blk-mq during DM suspend

DM uses blk-mq's quiesce/unquiesce to stop/start device mapper queue.

But blk-mq's unquiesce may come from outside events, such as elevator
switch, updating nr_requests or others, and request may come during
suspend, so simply ask for blk-mq to requeue it.

Fixes one kernel panic issue when running updating nr_requests and
dm-mpath suspend/resume stress test.

Cc: stable@vger.kernel.org
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>

drivers/md/dm-rq.c

@@ -490,6 +490,14 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 	struct mapped_device *md = tio->md;
 	struct dm_target *ti = md->immutable_target;
 
+	/*
+	 * blk-mq's unquiesce may come from outside events, such as
+	 * elevator switch, updating nr_requests or others, and request may
+	 * come during suspend, so simply ask for blk-mq to requeue it.
+	 */
+	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)))
+		return BLK_STS_RESOURCE;
+
 	if (unlikely(!ti)) {
 		int srcu_idx;
 		struct dm_table *map = dm_get_live_table(md, &srcu_idx);