From 09dff43565bd06e310e29b0309b5547ee3b86a21 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 21 Apr 2010 13:02:07 -0700
Subject: [PATCH] --- yaml --- r: 190536 b: refs/heads/master c:
 8b08ca52f5942c21564bbb90ccfb61053f2c26a1 h: refs/heads/master v: v3

---
 [refs]               |  2 +-
 trunk/kernel/sched.c | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/[refs] b/[refs]
index ae9e010d028d..6e4810637173 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 4b402210486c6414fe5fbfd85934a0a22da56b04
+refs/heads/master: 8b08ca52f5942c21564bbb90ccfb61053f2c26a1
diff --git a/trunk/kernel/sched.c b/trunk/kernel/sched.c
index de0bd26e520a..3c2a54f70ffe 100644
--- a/trunk/kernel/sched.c
+++ b/trunk/kernel/sched.c
@@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p)
 /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
 static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 {
+	/*
+	 * Strictly speaking this rcu_read_lock() is not needed since the
+	 * task_group is tied to the cgroup, which in turn can never go away
+	 * as long as there are tasks attached to it.
+	 *
+	 * However since task_group() uses task_subsys_state() which is an
+	 * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.
+	 */
+	rcu_read_lock();
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
 	p->se.parent = task_group(p)->se[cpu];
@@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
 	p->rt.rt_rq  = task_group(p)->rt_rq[cpu];
 	p->rt.parent = task_group(p)->rt_se[cpu];
 #endif
+	rcu_read_unlock();
 }
 
 #else