linux-kernel - [PATCH 3/5] sched: Fix an RCU warning in print

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Date:	Thu, 22 Apr 2010 17:30:40 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	LKML <linux-kernel@...r.kernel.org>
CC:	"containers@...ts.osdl.org" <containers@...ts.osdl.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 3/5] sched: Fix an RCU warning in print_task()

With CONFIG_PROVE_RCU=y, a warning can be triggered:

  $ cat /proc/sched_debug

...
kernel/cgroup.c:1649 invoked rcu_dereference_check() without protection!
...

Both cgroup_path() and task_group() should be called with either
rcu_read_lock or cgroup_mutex held.

Signed-off-by: Li Zefan <lizf@...fujitsu.com>
---
 kernel/sched_debug.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 9cf1baf..87a330a 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -114,7 +114,9 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 	{
 		char path[64];
 
+		rcu_read_lock();
 		cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
+		rcu_read_unlock();
 		SEQ_printf(m, " %s", path);
 	}
 #endif
-- 
1.6.3

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