linux-kernel - Re: [patch] sched: fix broken SCHED_RESET_ON

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Date:	Wed, 27 Jul 2011 18:10:35 +0200
From:	Mike Galbraith <efault@....de>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch] sched: fix broken SCHED_RESET_ON_FORK handling

I knew that thing had been moved before.. see f83f9ac2.

On Wed, 2011-07-27 at 17:14 +0200, Mike Galbraith wrote:
> sched: fix broken SCHED_RESET_ON_FORK handling
> 
> Setting child->prio = current->normal_prio _after_ SCHED_RESET_ON_FORK has
> been handled for an RT parent gives birth to a deranged mutant child with
> non-RT policy, but RT prio and sched_class.
> 
> Move PI leakage protection up, always set priorities and weight, and if the
> child is leaving RT class, reset rt_priority to the proper value.
> 
> Signed-off-by: Mike Galbraith <efault@....de>
> Cc: <stable@...nel.org>
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 0281f84..a3e65a0 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2804,19 +2804,23 @@ void sched_fork(struct task_struct *p)
>  	p->state = TASK_RUNNING;
>  
>  	/*
> +	 * Make sure we do not leak PI boosting priority to the child.
> +	 */
> +	p->prio = current->normal_prio;
> +
> +	/*
>  	 * Revert to default priority/policy on fork if requested.
>  	 */
>  	if (unlikely(p->sched_reset_on_fork)) {
> -		if (p->policy == SCHED_FIFO || p->policy == SCHED_RR) {
> +		if (task_has_rt_policy(p)) {
>  			p->policy = SCHED_NORMAL;
> -			p->normal_prio = p->static_prio;
> -		}
> -
> -		if (PRIO_TO_NICE(p->static_prio) < 0) {
>  			p->static_prio = NICE_TO_PRIO(0);
> -			p->normal_prio = p->static_prio;
> -			set_load_weight(p);
> -		}
> +			p->rt_priority = 0;
> +		} else if (PRIO_TO_NICE(p->static_prio) < 0)
> +			p->static_prio = NICE_TO_PRIO(0);
> +
> +		p->prio = p->normal_prio = __normal_prio(p);
> +		set_load_weight(p);
>  
>  		/*
>  		 * We don't need the reset flag anymore after the fork. It has
> @@ -2825,11 +2829,6 @@ void sched_fork(struct task_struct *p)
>  		p->sched_reset_on_fork = 0;
>  	}
>  
> -	/*
> -	 * Make sure we do not leak PI boosting priority to the child.
> -	 */
> -	p->prio = current->normal_prio;
> -
>  	if (!rt_prio(p->prio))
>  		p->sched_class = &fair_sched_class;
>  
> 
> 


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