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Date: Sun, 2 Aug 2015 00:36:09 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@redhat.com>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/6] stop_machine: kill stop_cpus_lock and
 lg_double_lock/unlock()
Message-ID: <20150801223609.GD25159@twins.programming.kicks-ass.net>
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 <20150801105718.GA13901@redhat.com>
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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.