blk-mq: clear active_queues before clearing BLK_MQ_F_TAG_QUEUE_SHARED

We run a test that delete and recover devcies frequently(two devices on
the same host), and we found that 'active_queues' is super big after a
period of time.

If device a and device b share a tag set, and a is deleted, then
blk_mq_exit_queue() will clear BLK_MQ_F_TAG_QUEUE_SHARED because there
is only one queue that are using the tag set. However, if b is still
active, the active_queues of b might never be cleared even if b is
deleted.

Thus clear active_queues before BLK_MQ_F_TAG_QUEUE_SHARED is cleared.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210731062130.1533893-1-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -2994,10 +2994,12 @@ static void queue_set_hctx_shared(struct request_queue *q, bool shared)
 	int i;
 
 	queue_for_each_hw_ctx(q, hctx, i) {
-		if (shared)
+		if (shared) {
 			hctx->flags |= BLK_MQ_F_TAG_QUEUE_SHARED;
-		else
+		} else {
+			blk_mq_tag_idle(hctx);
 			hctx->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED;
+		}
 	}
 }