linux-kernel - Re: [PATCH} - There appears to be a minor race condition in sched.c

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Message-ID: <20090326075101.GE24227@balbir.in.ibm.com>
Date:	Thu, 26 Mar 2009 13:21:01 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Piet Delaney <piet.delaney@...silica.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Johannes Weiner <jw@...ix.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH} - There appears  to be a minor race condition in
	sched.c

* Piet Delaney <piet.delaney@...silica.com> [2009-03-25 20:46:11]:

> Ingo, Peter:
>
> There appears to be a minor race condition in sched.c where
> you can get a division by zero. I suspect that it only shows
> up when the kernel is compiled without optimization and the code
> loads rq->nr_running from memory twice.
>
> It's part of our SMP stabilization changes that I just posted to:
>
>     git://git.kernel.org/pub/scm/linux/kernel/git/piet/xtensa-2.6.27-smp.git
>
> I mentioned it to Johannes the other day and he suggested passing it on to you ASAP.
>

The latest version uses ACCESS_ONCE to get rq->nr_running and then
uses that value. I am not sure what version you are talking about, if
it is older, you should consider backporting from the current version.


-- 
	Balbir
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