linux-kernel - RE: [PATCH v9 12/12] x86, topology: Debug CPU00 hotplug

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Date:	Wed, 17 Oct 2012 00:06:12 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	Arjan Dan De Ven <arjan@...ux.intel.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: RE: [PATCH v9 12/12] x86, topology: Debug CPU00 hotplug

> > +#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
 > +	case PM_RESTORE_PREPARE:
> > +		/*
> > +		 * When system resumes from hibernation, online CPU0
> because
> > +		 * 1. it's required for resume and
> > +		 * 2. the CPU was online before hibernation
> > +		 */
> > +		if (!cpu_online(0))
> > +			_debug_hotplug_cpu(0, 1);
> 
> This won't work. CPU hotplug is disabled by cpu_hotplug_pm_callback()
> during
> PM_HIBERNATION_PREPARE and is enabled back only during
> PM_POST_HIBERNATION.
> 
> So calls to cpu_up() or cpu_down() will fail in the meantime.

The code works just fine.

You are talking about hibernation/suspend phase. This piece of
code is all about restore phase. Of course you can call cpu_up()
and cpu_down() during restore phase.

So there is no problem here.

Thanks.

-Fenghua

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