linux-kernel - [PATCH tip/core/urgent 1/3] rcu: fix lockdep splat in wake

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Message-Id: <1276640983-14641-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date:	Tue, 15 Jun 2010 15:29:41 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com,
	Daniel J Blueman <daniel.blueman@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/urgent 1/3] rcu: fix lockdep splat in wake_affine()

From: Daniel J Blueman <daniel.blueman@...il.com>

With 2.6.35-rc1 and your patch in the context below, we still see
"include/linux/cgroup.h:534 invoked rcu_dereference_check() without
protection!", so need this additional patch:

Acquire read-side RCU lock around task_group() calls, addressing
"include/linux/cgroup.h:534 invoked rcu_dereference_check() without
protection!" warning.

Signed-off-by: Daniel J Blueman <daniel.blueman@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/sched_fair.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index eed35ed..ca56133 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1240,6 +1240,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 	 * effect of the currently running task from the load
 	 * of the current CPU:
 	 */
+	rcu_read_lock();
 	if (sync) {
 		tg = task_group(current);
 		weight = current->se.load.weight;
@@ -1249,6 +1250,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 	}
 
 	tg = task_group(p);
+	rcu_read_unlock();
 	weight = p->se.load.weight;
 
 	/*
-- 
1.7.0.6

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