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

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Date:	Tue, 20 May 2014 09:08:53 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	Peter Zijlstra <peterz@...radead.org>
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()



20.05.2014, 04:00, "Peter Zijlstra" <peterz@...radead.org>:
> 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);

But p->pi_lock is not held. The problem is __task_rq_lock() has lockdep assert.
Should we change it?

Kirill
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