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

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Date:	Wed, 29 Dec 2010 22:20:19 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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 Fri, Dec 24, 2010 at 01:23:45PM +0100, Peter Zijlstra wrote:
> Currently p->pi_lock already serializes p->sched_class, also put
> p->cpus_allowed and try_to_wake_up() under it, this prepares the way
> to do the first part of ttwu() without holding rq->lock.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/sched.c |   37 ++++++++++++++++---------------------
>  1 file changed, 16 insertions(+), 21 deletions(-)
> 
> Index: linux-2.6/kernel/sched.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched.c
> +++ linux-2.6/kernel/sched.c
> @@ -2301,7 +2301,7 @@ void task_oncpu_function_call(struct tas
>  
>  #ifdef CONFIG_SMP
>  /*
> - * ->cpus_allowed is protected by either TASK_WAKING or rq->lock held.
> + * ->cpus_allowed is protected by both rq->lock and p->pi_lock
>   */
>  static int select_fallback_rq(int cpu, struct task_struct *p)
>  {
> @@ -2334,7 +2334,7 @@ static int select_fallback_rq(int cpu, s
>  }
>  
>  /*
> - * 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?

Thanks,
Yong
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