diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 20a8193..ebca7c0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3647,6 +3647,9 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
 	 */
 	BUG_ON(!thresholds);
 
+	if (!thresholds->primary)
+		goto unlock;
+
 	usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
 
 	/* Check if a threshold crossed before removing */
@@ -3695,7 +3698,7 @@ swap_buffers:
 
 	/* To be sure that nobody uses thresholds */
 	synchronize_rcu();
-
+unlock:
 	mutex_unlock(&memcg->thresholds_lock);
 }