linux-kernel - Re: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference

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Date:	Mon, 19 Apr 2010 11:45:22 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
CC:	Eric Paris <eparis@...isplace.org>,
	Miles Lane <miles.lane@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492
 invoked rcu_dereference_check() without protection!

Should be [tip:core/urgent]

Acked-by: Lai Jiangshan <laijs@...fujitsu.com>

Paul E. McKenney wrote:
> 
> Looks reasonable to me!
> 
> Acked-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
>> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>> ---
>>  kernel/sched.c |   10 ++++++++++
>>  1 files changed, 10 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/sched.c b/kernel/sched.c
>> index 3acf694..2e06d87 100644
>> --- a/kernel/sched.c
>> +++ b/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
>>
>>
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