linux-kernel - Re: [patch] sched: prevent bound kthreads from changing cpus

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Message-ID: <20080610174750.GA6064@tv-sign.ru>
Date:	Tue, 10 Jun 2008 21:47:50 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Paul Menage <menage@...gle.com>, Paul Jackson <pj@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] sched: prevent bound kthreads from changing cpus_allowed

On 06/05, David Rientjes wrote:
>
> Kthreads that have called kthread_bind() are bound to specific cpus, so
> other tasks should not be able to change their cpus_allowed from under
> them.  Otherwise, it is possible to move kthreads, such as the migration
> or software watchdog threads, so they are not allowed access to the cpu
> they work on.

Imho, this is very good change, but...

> @@ -180,6 +180,7 @@ void kthread_bind(struct task_struct *k, unsigned int cpu)
>  	set_task_cpu(k, cpu);
>  	k->cpus_allowed = cpumask_of_cpu(cpu);
>  	k->rt.nr_cpus_allowed = 1;
> +	k->flags |= PF_THREAD_BOUND;

What if user-space moves this task right before "|= PF_THREAD_BOUND" ?

Oleg.

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