linux-kernel - Re: [PATCH 1/3] stop_machine: check work->done while handling enqueued works

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Message-ID: <20130207163739.GN2875@htj.dyndns.org>
Date:	Thu, 7 Feb 2013 08:37:39 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] stop_machine: check work->done while handling
 enqueued works

Hello, Hillf.

On Thu, Feb 07, 2013 at 08:13:44PM +0800, Hillf Danton wrote:
> > If this is meant as a pure cleanup, I'm not sure it's an improvement.
> > You own your cpu_stop_done until you call cpu_stop_signal_done() on
> > it, so I don't think there's anything wrong with the current code.
> > The new code is different, not necessarily better.
> 
> The comment just above cpu_stop_signal_done()
> says it is not certain that the input done is valid, so
> I did this work.
> Plus works enqueued through stop_one_cpu_nowait()
> do carry no done.

So, are you saying that we can hit NULL deref in cpu_stopper_thread()
and this is a bug fix?  If so, can you please redo the description?  I
really can't tell what the patch is trying to do from the original
description.

Thanks.

-- 
tejun
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