linux-kernel - Re: [RFC][PATCH 07/17] sched: Serialize p->cpus_allowed and ttwu() using p->pi

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Date:	Mon, 03 Jan 2011 12:12:14 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	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>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 07/17] sched: Serialize p->cpus_allowed and ttwu()
 using p->pi_lock

On Wed, 2010-12-29 at 22:20 +0800, Yong Zhang wrote:
> > - * The caller (fork, wakeup) owns TASK_WAKING, ->cpus_allowed is stable.
> > + * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable.
> 
> Yes for wakeup, but not true for fork.
> I don't see protection in wake_up_new_task().
> Or am I missing something? 

Ah, true, wake_up_new_task() holds task_rq_lock() which is sufficient,
but yes, we could also make that pi_lock.


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