linux-kernel - Re: [RFC][PATCH 12/17] sched: Also serialize ttwu_local() with p->pi

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Date:	Sun, 9 Jan 2011 18:11:42 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Chris Mason <chris.mason@...cle.com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 12/17] sched: Also serialize ttwu_local() with
 p->pi_lock

Hello,

On Mon, Jan 03, 2011 at 06:32:54PM +0100, Oleg Nesterov wrote:
> > @@ -2523,16 +2523,21 @@ static void try_to_wake_up_local(struct
> >
> >  	BUG_ON(rq != this_rq());
> >  	BUG_ON(p == current);
> > -	lockdep_assert_held(&rq->lock);
> > +
> > +	raw_spin_unlock(&rq->lock);
> > +	raw_spin_lock(&p->pi_lock);
> > +	raw_spin_lock(&rq->lock);
> 
> I _think_ this is safe, this worker can't change cpu afaics. But
> probably Tejun can take a look, just in case.

Yeah, preemption is disabled so it should be safe.  Only bound workers
can be woken up by ttwu_local.  They get migrated to another CPU only
during CPU offlining.  Both CPU offlining and task exit wouldn't
happen while preemption is disabled so it should be safe.

Thanks.

-- 
tejun
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