linux-kernel - Re: [PATCH RFC] sched: Revert delayed_put_task

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Message-ID: <20141016080106.GD7369@worktop.fdxtended.com>
Date:	Thu, 16 Oct 2014 10:01:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Kirill Tkhai <ktkhai@...allels.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Kirill Tkhai <tkhai@...dex.ru>
Subject: Re: [PATCH RFC] sched: Revert delayed_put_task_struct() and fix use
 after free

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().
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