[PATCH] memcontrol: rcu_read_lock() to protect mm_match_cgroup()

[Lai Jiangshan <laijs@cn.fujitsu.com>]

mm_match_cgroup() calls cgroup_subsys_state().

we must use rcu_read_lock() to protect cgroup_subsys_state().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 1fbe14d..ce89ff0 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -47,8 +47,15 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
-#define mm_match_cgroup(mm, cgroup)	\
-	((cgroup) == mem_cgroup_from_task((mm)->owner))
+static inline
+int mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *cgroup)
+{
+	struct mem_cgroup *mem;
+	rcu_read_lock();
+	mem = mem_cgroup_from_task((mm)->owner);
+	rcu_read_unlock();
+	return cgroup == mem;
+}
 
 extern int
 mem_cgroup_prepare_migration(struct page *page, struct page *newpage);