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Date: Thu, 16 Oct 2014 10:01:06 +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: <20141016080106.GD7369@worktop.fdxtended.com>
References: <1413376300.24793.55.camel@tkhai>
 <20141015150641.GA2755@redhat.com>
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On Wed, Oct 15, 2014 at 05:06:41PM +0200, Oleg Nesterov wrote:
> 
> At least the code like
> 
> 	rcu_read_lock();
> 	get_task_struct(foreign_rq->curr);
> 	rcu_read_unlock();
> 
> is certainly wrong. And _probably_ the problem should be fixed here. Perhaps
> we can add try_to_get_task_struct() which does atomic_inc_not_zero() ...

There is an rcu_read_lock() around it through task_numa_compare().