linux-kernel - Re: [RFC][PATCH] sched: Fix TASK_DEAD race in finish_task

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Message-ID: <CA+55aFy6j3YFF6vZDgT4cX62L02bqRBDDx0MaR+qT-rmG+a0wA@mail.gmail.com>
Date:	Tue, 29 Sep 2015 13:41:50 -0400
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Manfred Spraul <manfred@...orfullife.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [RFC][PATCH] sched: Fix TASK_DEAD race in finish_task_switch()

On Tue, Sep 29, 2015 at 12:50 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> The control dependency creates a LOAD->STORE order, that is, no STOREs
> can happen until we observe !p->on_cpu.

Fair enough.

> Right, but wmb isn't sufficient as it doesn't order the prev->state LOAD
> vs the prev->on_cpu = 0 STORE. If those happen in the wrong order the
> described race can happen and we get a use-after-free.

.. and you convinced me. The patch is good. Ack.

               Linus
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