linux-kernel - Re: [PATCH v2 4/7] sched/deadline: reschedule if stop task slip in after pull operations

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Message-ID: <BLU437-SMTP734C1EA56490F7E530FC2280B70@phx.gbl>
Date:	Sun, 31 May 2015 08:06:16 +0800
From:	Wanpeng Li <wanpeng.li@...mail.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
CC:	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] sched/deadline: reschedule if stop task slip in
 after pull operations


On 5/29/15 10:16 PM, Peter Zijlstra wrote:
> On Wed, May 13, 2015 at 02:01:04PM +0800, Wanpeng Li wrote:
>> pull_dl_task can drop (and re-acquire) rq->lock, this means a stop task
>> can slip in, in which case we need to reschedule. This patch add the
>> reschedule when the scenario occurs.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
>> ---
>>   kernel/sched/deadline.c | 16 +++++++++++++++-
>>   1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
>> index e49b1e6..7d4c4fc 100644
>> --- a/kernel/sched/deadline.c
>> +++ b/kernel/sched/deadline.c
>> @@ -1750,7 +1750,13 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
>>   	if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
>>   		return;
>>   
>> -	if (pull_dl_task(rq))
>> +	/*
>> +	 * pull_dl_task() can drop (and re-acquire) rq->lock; this
>> +	 * means a stop task can slip in, in which case we need to
>> +	 * reschedule.
>> +	 */
>> +	if (pull_dl_task(rq) ||
>> +		(rq->stop && task_on_rq_queued(rq->stop)))
>>   		resched_curr(rq);
> But, the waking of the stop task will already have done the preemption
> check and won (obviously). So the wakeup should already have done the
> resched_curr().

Indeed, thanks for your pointing out. :)

>
> So why?
>
> --
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