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

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Date:	Sun, 2 Oct 2011 12:50:23 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"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

Hello,

On Mon, Oct 03, 2011 at 12:35:04AM +0530, Srivatsa S. Bhat wrote:
> So, this patch addresses this issue by ensuring that microcode is not freed
> from kernel memory, nor invalidated when a CPU goes offline. Thus once the
> kernel gets the microcode during boot-up, it will never have to depend on
> userspace ever again to get microcode, since it never releases the copy it
> already has. So every run of the microcode callback for CPU online event will
> now succeed irrespective of whether userspace is frozen or not. As a result,
> this fixes the task freezing failure encountered while running CPU hotplug
> stress test along with suspend/resume operations simultaneously.

I'm not familiar with how microcode is supposed to be managed but is
it impossible for the newly hotplugged CPU (an actual hot unplug /
plug) may not like the microcode loaded for the previous CPU?  Isn't
that why CPU_DEAD was invalidating the microcode?

Thanks.

-- 
tejun
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