From: Jiang Biao <jiang.biao2@zte.com.cn>
Date: Thu, 19 Apr 2018 12:06:09 +0800
Subject: [PATCH] blkcg: init root blkcg_gq under lock
Git-commit: 901932a3f9b2b80352896be946c6d577c0a9652c
Patch-mainline: v4.17-rc3
References: bsc#1104967,FATE#325924

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@zte.com.cn>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
CC: Tejun Heo <tj@kernel.org>
CC: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/blk-cgroup.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 79da2a723b68..eb85cb87c40f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1181,18 +1181,16 @@ int blkcg_init_queue(struct request_queue *q)
 	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);
@@ -1200,6 +1198,13 @@ int blkcg_init_queue(struct request_queue *q)
 		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);
 }
 
 /**
-- 
2.16.4