linux-kernel - Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures

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Date:	Tue, 4 Oct 2011 15:25:58 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, tigran@...azian.fsnet.co.uk,
	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task
 freezing failures

On Tue, Oct 04, 2011 at 12:15:08AM -0700, Tejun Heo wrote:
> On Mon, Oct 03, 2011 at 10:47:54AM +0200, Borislav Petkov wrote:
> > I think your patch makes sense because re-loading the ucode during
> > a suspend/resume cycle is unnecessary. If one wants to update the
> > microcode, it should happen later when the box is resumed again: you
> > simply put the new microcode image in /lib/firmware/... and on AMD
> > unload/reload the microcode module and on Intel you do either that or
> > use the deprecated microcode_ctl.
> 
> I don't think it changes anything for suspend/resume cycles.  They're
> different hooks.  The proposed patch changes actual cpu hotplug paths.

Well, we're offlining the CPUs through the same hotplug path when
suspending and since currently the microcode core unnecessarily
re-requests the ucode image from userspace on resume, I still think the
patch makes sense. Especially if Srivatsa does suspend/resume and CPU
hotplugging simultaneously in a test and upon onlining a CPU, he manages
of doing request_firmware on a frozen userspace.

Srivatsa, is my understanding correct?

Thanks.

-- 
Regards/Gruss,
Boris.
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