blkcg: delete redundant get/put operations for queue

When calling blkcg_schedule_throttle(), for the same queue,
redundant get/put operations can be removed.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -1757,12 +1757,15 @@ void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay)
 	if (unlikely(current->flags & PF_KTHREAD))
 		return;
 
-	if (!blk_get_queue(q))
-		return;
+	if (current->throttle_queue != q) {
+		if (!blk_get_queue(q))
+			return;
+
+		if (current->throttle_queue)
+			blk_put_queue(current->throttle_queue);
+		current->throttle_queue = q;
+	}
 
-	if (current->throttle_queue)
-		blk_put_queue(current->throttle_queue);
-	current->throttle_queue = q;
 	if (use_memdelay)
 		current->use_memdelay = use_memdelay;
 	set_notify_resume(current);