linux-kernel - Re: [RFC PATCH] cpuset: fix cpuset_cpus_allowed_fallback() don't update tsk->rt.nr_cpus

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Date:	Thu, 28 Apr 2011 18:11:49 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Li Zefan <lizf@...fujitsu.com>,
	Miao Xie <miaox@...fujitsu.com>
Subject: Re: [RFC PATCH] cpuset: fix cpuset_cpus_allowed_fallback() don't
	update tsk->rt.nr_cpus_allowed

On 04/28, KOSAKI Motohiro wrote:
>
> Oleg, Peter,
>
> I apologize if I misunderstand a code.

Heh, I bet you understand it better than me ;)

> index f20eb8f..42dcbdc 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -147,6 +147,7 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
>  static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
>  {
>  	cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
> +	p->rt.nr_cpus_allowed = cpumask_weight(&p->cpus_allowed);
>  	return cpumask_any(cpu_active_mask);
>  }
>
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 1ceeb04..6e5bbe8 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -2220,6 +2220,7 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
>  		cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask);
>  		cpu = cpumask_any(cpu_active_mask;
>  	}
> +	tsk->rt.nr_cpus_allowed = cpumask_weight(&tsk->cpus_allowed);

I think you are right...

But, don't we need sched_class->set_cpus_allowed() in this case? Only for
consistency, iiuc currently it is not needed because the task is not active.

IOW, perhaps cpuset_cpus_allowed_fallback() should do


	if (p->sched_class->set_cpus_allowed)
		p->sched_class->set_cpus_allowed(p, cpu_possible_mask);
	else {
		cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
		p->rt.nr_cpus_allowed = cpumask_weight(cpu_possible_mask);
	}

?

If yes, probably the new do_set_cpus_allowed(p, mask) helper makes sense,
it can be used by set_cpus_allowed_ptr() too.

Oleg.

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