[PATCH] blk-cgroup: Call cgroup_path only under cgroup lock

[Sasha Levin <levinsasha928@gmail.com>]

Since we can't keep rcu read lock during blkg_alloc(), we currently
call cgroup_path() without any locks at all.

This patch adds cgroup locking before calling cgroup_path.

This also fixes a lockdep warning on boot.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 block/blk-cgroup.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index cb6b176..b5f539c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -508,7 +508,9 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
 	INIT_LIST_HEAD(&blkg->q_node);
 	blkg->blkcg = blkcg;
 	blkg->refcnt = 1;
+	cgroup_lock();
 	cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
+	cgroup_unlock();
 
 	for (i = 0; i < BLKIO_NR_POLICIES; i++) {
 		struct blkio_policy_type *pol = blkio_policy[i];
-- 
1.7.8.4