blkcg: init root blkcg_gq under lock

BugLink: http://bugs.launchpad.net/bugs/1794889
[ 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@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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 0bc4b8ac9f659ac842ffeb3a0b28c2fbfe65b138..2b33be93c52f98b5075a0222c5afdf427672d5b4 100644 (file)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1149,18 +1149,16 @@ 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);
@@ -1168,6 +1166,13 @@ 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);
 }
 
 /**