linux-kernel - Re: [PATCH] clockevent: don't remove broadcast device when cpu is dead

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Date:	Wed, 13 Jan 2010 23:08:49 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Xiaotian Feng <dfeng@...hat.com>
cc:	linux-kernel@...r.kernel.org, Magnus Damm <damm@...l.co.jp>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>
Subject: Re: [PATCH] clockevent: don't remove broadcast device when cpu is
 dead

On Wed, 13 Jan 2010, Xiaotian Feng wrote:
> On 01/12/2010 09:20 PM, Thomas Gleixner wrote:
> > On Thu, 7 Jan 2010, Xiaotian Feng wrote:
> > 
> > > Marc reported BUG during shutdown, after debugging, kernel is trying
> > > to remove a broadcast device which mode is CLOCK_EVT_MODE_ONESHOT.
> > > 
> > > The root cause for this bug is that in clockevents_notify,
> > > "cpumask_weight(dev->cpumask) == 1" is always true even if dev is a
> > 
> > Why is cpumask_weight(dev->cpumask) == 1 always true when we shutdown
> > a non boot cpu ?
> > 
> > The broadcast device is not a per cpu device and the cpumask should
> > not only contain the CPU which is shut down !
> 
> At least for hpet broadcast dev, it's dev->cpumask is only contain the CPU
> which it is initialized from.

Which is fundamentaly wrong and the root cause of the problem. I'll
have a look tomorrow morning when my brain is more awake than now.

> And for broadcast device, kernel is using tick_broadcast_mask not
> dev->cpumask, right?

No, tick_broadcast_mask is the bitmask which tells us which cpus get
the broadcast IPI.

Thanks,

	tglx
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