linux-kernel - Re: [PATCH] sched/dl: Fix race between dl_task_timer() and sched

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Message-ID: <20140520000026.GD11096@twins.programming.kicks-ass.net>
Date:	Tue, 20 May 2014 02:00:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Juri Lelli <juri.lelli@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] sched/dl: Fix race between dl_task_timer() and
 sched_setaffinity()

On Mon, May 19, 2014 at 11:31:19PM +0400, Kirill Tkhai wrote:
> @@ -513,9 +513,17 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
>  						     struct sched_dl_entity,
>  						     dl_timer);
>  	struct task_struct *p = dl_task_of(dl_se);
> -	struct rq *rq = task_rq(p);
> +	struct rq *rq;
> +again:
> +	rq = task_rq(p);
>  	raw_spin_lock(&rq->lock);
>  
> +	if (unlikely(rq != task_rq(p))) {
> +		/* Task was moved, retrying. */
> +		raw_spin_unlock(&rq->lock);
> +		goto again;
> +	}
> +

That thing is called: rq = __task_rq_lock(p);

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