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Subject: Re: [PATCH 1/3] stop_machine: kill __stop_machine()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Tejun Heo <tj@kernel.org>
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Date: Thu, 16 Jun 2011 20:36:02 +0200
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On Thu, 2011-06-16 at 20:28 +0200, Tejun Heo wrote:
> Peter, I don't think it's that simple.  get_online_cpus() itself can't
> create circular dependency by itself.  It allows recursing.  The chain
> involves cpu_hotplug_begin() which returns with hotplug mutex held.


Right, its like:

 mutex_lock(&a);
 get_online_cpus();

vs

 cpu_hotplug_begin()
 mutex_lock(&a);


that will really deadlock