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

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Date:	Tue, 20 May 2014 10:07:18 +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, 09:08, "Kirill Tkhai" <tkhai@...dex.ru>:
> 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?

Or make something like this?

static inline struct rq *_task_rq_lock(struct task_struct *p)
{
        lockdep_assert_held(&p->pi_lock);

        return __task_rq_lock(p);
}

Thanks!
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