linux-kernel - Re: [PATCH 2/2] sched_rt: protect rt_rq->rt_time by rt_runtime

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Date:	Thu, 05 Feb 2009 16:06:43 -0800
From:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched_rt: protect rt_rq->rt_time by rt_runtime_lock

Peter Zijlstra wrote:
> On Thu, 2009-02-05 at 15:38 -0800, Hiroshi Shimamoto wrote:
>> From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
>>
>> Impact: fix possible race condition
>>
>> rt_rq->rt_time should be protected.
> 
> Don't think so, all we do is check the value for non-zero outside the
> lock, that should be ok.
> 
> If there's still a race, your changelog utterly fails to mention the
> race scenario.

OK. I just noticed rt_time is accessed with rt_runtime_lock held except
this point. Will look at this again.

Thanks,
Hiroshi

> 
>> Signed-off-by: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
>> ---
>>  kernel/sched_rt.c |    4 ++--
>>  1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
>> index 299d012..d7654a3 100644
>> --- a/kernel/sched_rt.c
>> +++ b/kernel/sched_rt.c
>> @@ -496,10 +496,10 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
>>  		struct rq *rq = rq_of_rt_rq(rt_rq);
>>  
>>  		spin_lock(&rq->lock);
>> +		spin_lock(&rt_rq->rt_runtime_lock);
>>  		if (rt_rq->rt_time) {
>>  			u64 runtime;
>>  
>> -			spin_lock(&rt_rq->rt_runtime_lock);
>>  			if (rt_rq->rt_throttled)
>>  				balance_runtime(rt_rq);
>>  			runtime = rt_rq->rt_runtime;
>> @@ -510,9 +510,9 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun)
>>  			}
>>  			if (rt_rq->rt_time || rt_rq->rt_nr_running)
>>  				idle = 0;
>> -			spin_unlock(&rt_rq->rt_runtime_lock);
>>  		} else if (rt_rq->rt_nr_running)
>>  			idle = 0;
>> +		spin_unlock(&rt_rq->rt_runtime_lock);
>>  
>>  		if (enqueue)
>>  			sched_rt_rq_enqueue(rt_rq);
> 
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