linux-kernel - Re: [PATCH v2 6/6] stop_machine: kill stop_cpus_lock and lg_double

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Message-ID: <20150801223609.GD25159@twins.programming.kicks-ass.net>
Date:	Sun, 2 Aug 2015 00:36:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/6] stop_machine: kill stop_cpus_lock and
 lg_double_lock/unlock()

On Sat, Aug 01, 2015 at 12:57:18PM +0200, Oleg Nesterov wrote:

> > > +	if (stop_work_pending(stopper1) != stop_work_pending(stopper2))
> > > +		goto unlock;
> >
> > You could DoS/false positive this by running stop_one_cpu() in a loop,
> > and thereby 'always' having work pending on one but not the other.
> 
> IIRC no. I am pretty sure stop_one_cpu() doesn't use stopper->stop_work,
> only stop_machine() does.

Urgh, I missed you were testing the cpu_stopper::stop_work not the
cpu_stopper::works list.


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