[PATCH] cpuset: rcu_read_lock() to protect task_cs() even we don't dereference to task_cs()'s return value

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

task_cs() calls cgroup_subsys_state().

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

in current_cpuset_is_being_rebound(), we don't dereference to task_cs()'s
return value, but task_cs() accesses css_set, this css_set maybe freed
when task_cs() called.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3e00526..e0e087e 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1141,7 +1136,11 @@ done:
 
 int current_cpuset_is_being_rebound(void)
 {
-	return task_cs(current) == cpuset_being_rebound;
+	struct cpuset *cs;
+	rcu_read_lock();
+	cs = task_cs(current);
+	rcu_read_unlock();
+	return cs == cpuset_being_rebound;
 }
 
 static int update_relax_domain_level(struct cpuset *cs, s64 val)