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Date: Thu, 16 Oct 2014 09:56:50 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Kirill Tkhai <ktkhai@parallels.com>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: [PATCH RFC] sched: Revert delayed_put_task_struct() and fix use
 after free
Message-ID: <20141016075650.GB7369@worktop.fdxtended.com>
References: <1413376300.24793.55.camel@tkhai>
 <20141015150641.GA2755@redhat.com>
 <20141015194044.GA4557@redhat.com>
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On Wed, Oct 15, 2014 at 09:40:44PM +0200, Oleg Nesterov wrote:
> What do you think?
> 
> Oleg.
> 
> --- x/kernel/sched/fair.c
> +++ x/kernel/sched/fair.c
> @@ -1165,7 +1165,7 @@ static void task_numa_compare(struct tas
>  
>  	rcu_read_lock();
>  	cur = ACCESS_ONCE(dst_rq->curr);
> -	if (cur->pid == 0) /* idle */
> +	if (is_idle_task(cur) || (curr->flags & PF_EXITING))
>  		cur = NULL;
>  
>  	/*

That makes sense, is_idle_task() is indeed the right function there, and
PF_EXITING avoids doing work where it doesn't make sense.