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

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Message-ID: <20150529143420.GR3644@twins.programming.kicks-ass.net>
Date:	Fri, 29 May 2015 16:34:20 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	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 7/7] sched/rt: reschedule if stop/dl task slip in
 after pull operations

On Wed, May 13, 2015 at 02:01:07PM +0800, Wanpeng Li wrote:
> pull_rt_task() can drop (and re-acquire) rq->lock, this means a dl 
> or stop task can slip in, in which case need to reschedule. This 
> patch add the reschedule when the scenario occurs.
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  kernel/sched/rt.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 560d2fa..8c948bf 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2136,7 +2136,14 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p)
>  	if (!task_on_rq_queued(p) || rq->rt.rt_nr_running)
>  		return;
>  
> -	if (pull_rt_task(rq))
> +	/*
> +	 * pull_rt_task() can drop (and re-acquire) rq->lock; this
> +	 * means a dl or stop task can slip in, in which case we need
> +	 * to reschedule.
> +	 */
> +	if (pull_rt_task(rq) ||
> +		(unlikely((rq->stop && task_on_rq_queued(rq->stop)) ||
> +			rq->dl.dl_nr_running)))
>  		resched_curr(rq);
>  }

Same as before; why is the normal wakeup preemption check not working?
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