1 files changed, 24 insertions, 0 deletions

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 14367499cfed..3b6a0e1265aa 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -463,6 +463,7 @@ static struct blkio_group *blkg_alloc(struct blkio_cgroup *blkcg,
         rcu_assign_pointer(blkg->q, q);
         blkg->blkcg = blkcg;
         blkg->plid = pol->plid;
+        blkg->refcnt = 1;
         cgroup_path(blkcg->css.cgroup, blkg->path, sizeof(blkg->path));
 
         /* alloc per-policy data */
@@ -633,6 +634,29 @@ void blkg_destroy_all(struct request_queue *q)
         }
 }
 
+static void blkg_rcu_free(struct rcu_head *rcu_head)
+{
+        blkg_free(container_of(rcu_head, struct blkio_group, rcu_head));
+}
+
+void __blkg_release(struct blkio_group *blkg)
+{
+        /* release the extra blkcg reference this blkg has been holding */
+        css_put(&blkg->blkcg->css);
+
+        /*
+         * A group is freed in rcu manner. But having an rcu lock does not
+         * mean that one can access all the fields of blkg and assume these
+         * are valid. For example, don't try to follow throtl_data and
+         * request queue links.
+         *
+         * Having a reference to blkg under an rcu allows acess to only
+         * values local to groups like group stats and group rate limits
+         */
+        call_rcu(&blkg->rcu_head, blkg_rcu_free);
+}
+EXPORT_SYMBOL_GPL(__blkg_release);
+
 static void blkio_reset_stats_cpu(struct blkio_group *blkg)
 {
         struct blkio_group_stats_cpu *stats_cpu;