blk-cgroup: fix missing put device in error path from blkg_conf_pref()

If blk_queue_enter() failed due to queue is dying, the
blkdev_put_no_open() is needed because blkcg_conf_open_bdev() succeeded.

Fixes: 0c9d338c ("blk-cgroup: synchronize blkg creation against policy deactivation")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20211102020705.2321858-1-yukuai3@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -640,7 +640,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 	 */
 	ret = blk_queue_enter(q, 0);
 	if (ret)
-		return ret;
+		goto fail;
 
 	rcu_read_lock();
 	spin_lock_irq(&q->queue_lock);
@@ -676,13 +676,13 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 		new_blkg = blkg_alloc(pos, q, GFP_KERNEL);
 		if (unlikely(!new_blkg)) {
 			ret = -ENOMEM;
-			goto fail;
+			goto fail_exit_queue;
 		}
 
 		if (radix_tree_preload(GFP_KERNEL)) {
 			blkg_free(new_blkg);
 			ret = -ENOMEM;
-			goto fail;
+			goto fail_exit_queue;
 		}
 
 		rcu_read_lock();
@@ -722,9 +722,10 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 fail_unlock:
 	spin_unlock_irq(&q->queue_lock);
 	rcu_read_unlock();
+fail_exit_queue:
+	blk_queue_exit(q);
 fail:
 	blkdev_put_no_open(bdev);
-	blk_queue_exit(q);
 	/*
 	 * If queue was bypassing, we should retry.  Do so after a
 	 * short msleep().  It isn't strictly necessary but queue