linux-kernel - Re: 2.6.29-rc1 does not boot

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Date:	Wed, 14 Jan 2009 12:30:06 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Maciej Rutecki <maciej.rutecki@...il.com>,
	Dieter Ries <clip2@....de>, travis@....com,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.29-rc1 does not boot

* Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Monday 12 January 2009 21:56:08 Ingo Molnar wrote:
> > work_on_cpu() needs to be reworked to be more generally usable.
> 
> Yes, but how?  If we don't take the hotplug lock, we are relying on the 
> callers to "prove" the cpu can't go away.  But we've already shown that 
> we can't find this by inspection :(

it appears the problem wasnt even the hotplug lock, but the fact that 
work_on_cpu() uses the generic schedule_work() method, which goes into a 
queue with all other keventsd worklets.

and keventd is used by other aspects of cpufreq as well -> creating 
workqueue-driven lock inversion scenarios - see Dieter's lockdep dump 
earlier in this thread. ( I'm amazed lockdep sees through that dependency
:-)

	Ingo
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