Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()"
 locks up on ARM
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Marc Zyngier <Marc.Zyngier@arm.com>, Yong Zhang <yong.zhang0@gmail.com>,
        Ingo Molnar <mingo@elte.hu>, Frank Rowand <frank.rowand@am.sony.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
In-Reply-To: <20110526170422.GA18413@redhat.com>
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Date: Thu, 26 May 2011 19:17:44 +0200
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On Thu, 2011-05-26 at 19:04 +0200, Oleg Nesterov wrote:
> On 05/26, Peter Zijlstra wrote:
> >
> > @@ -2636,7 +2636,8 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
> >  		 * to spin on ->on_cpu if p is current, since that would
> >  		 * deadlock.
> >  		 */
> > -		if (p == current) {
> > +		if (cpu == smp_processor_id()) {
> > +			p->sched_contributes_to_load = 0;
> >  			ttwu_queue(p, cpu);
> 
> Btw. I do not pretend I really understand se->vruntime, but in this
> case we are doing enqueue_task() without ->task_waking(), however we
> pass ENQUEUE_WAKING. Is it correct?

No its not, that's the thing that I got wrong the first time and caused
these pauses.


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