linux-kernel - Re: [PATCH] ACPI/Processor: Add CPU_STARTING_FROZEN check in the acpi_cpu_soft

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Date:	Wed, 06 Aug 2014 21:11:59 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Lan Tianyu <tianyu.lan@...el.com>
Cc:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Chen, Gong" <gong.chen@...ux.intel.com>
Subject: Re: [PATCH] ACPI/Processor: Add CPU_STARTING_FROZEN check in the acpi_cpu_soft_notify()

On Wednesday, August 06, 2014 11:02:05 AM Lan Tianyu wrote:
> On 2014年08月06日 09:30, Rafael J. Wysocki wrote:
> > On Friday, August 01, 2014 10:51:46 AM Lan Tianyu wrote:
> >> On 2014年08月01日 05:20, Rafael J. Wysocki wrote:
> >>> On Thursday, July 31, 2014 05:20:26 PM Lan Tianyu wrote:
> >>>> The callback of CPU_STARTING event can't sleep and so acpi_cpu_soft_notify()
> >>>> return directly when CPU_STARTING event is triggered. But cpu hotplug also
> >>>> happens during S2RAM. The action will become CPU_STARTING_FROZEN. This
> >>>> patch is to fix missing check the frozen event.
> > 
> > OK
> > 
> > What's the impact of the bug you're fixing?  Do we sleep when we shouldn't?
> > 
> > In particular, are there any bugs reported that are related to it?
> 
> So far, there is such bug report. I found the issue when test my patch
> of parallel non-boot cpu up with resuming device for S2RAM. Because
> original code will wait all cpu up and then do other resume task, the
> semaphore of ACPICA can always be get in the cpu notify callback and it
> will not fall in the sleep. It's different situation for paralleling
> non-boot cpu. The lock will be held by other threads and fall into
> sleep. Further thinking, this may not cause bug in the old kernel and it
> isn't needed by stable tree but the code should consider cpu frozen event.

OK, so we don't need to propagate this to -stable I'd say.

I'll queue it up for the second 3.17 pull request.

Rafael

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