[PATCH 4.14 039/189] blkcg: init root blkcg_gq under lock

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiang Biao <jiang.biao2@xxxxxxxxxx>

[ Upstream commit 901932a3f9b2b80352896be946c6d577c0a9652c ]

The initializing of q->root_blkg is currently outside of queue lock
and rcu, so the blkg may be destroied before the initializing, which
may cause dangling/null references. On the other side, the destroys
of blkg are protected by queue lock or rcu. Put the initializing
inside the queue lock and rcu to make it safer.

Signed-off-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
Signed-off-by: Wen Yang <wen.yang99@xxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
CC: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 block/blk-cgroup.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1149,18 +1149,16 @@ int blkcg_init_queue(struct request_queu
 	rcu_read_lock();
 	spin_lock_irq(q->queue_lock);
 	blkg = blkg_create(&blkcg_root, q, new_blkg);
+	if (IS_ERR(blkg))
+		goto err_unlock;
+	q->root_blkg = blkg;
+	q->root_rl.blkg = blkg;
 	spin_unlock_irq(q->queue_lock);
 	rcu_read_unlock();
 
 	if (preloaded)
 		radix_tree_preload_end();
 
-	if (IS_ERR(blkg))
-		return PTR_ERR(blkg);
-
-	q->root_blkg = blkg;
-	q->root_rl.blkg = blkg;
-
 	ret = blk_throtl_init(q);
 	if (ret) {
 		spin_lock_irq(q->queue_lock);
@@ -1168,6 +1166,13 @@ int blkcg_init_queue(struct request_queu
 		spin_unlock_irq(q->queue_lock);
 	}
 	return ret;
+
+err_unlock:
+	spin_unlock_irq(q->queue_lock);
+	rcu_read_unlock();
+	if (preloaded)
+		radix_tree_preload_end();
+	return PTR_ERR(blkg);
 }
 
 /**