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

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Message-ID: <20111004134653.GC3148@gere.osrc.amd.com>
Date:	Tue, 4 Oct 2011 15:46:53 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, "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 06:45:12PM +0530, Srivatsa S. Bhat wrote:
> I would like to propose a modified solution to the problem:
> 
> Taking a CPU offline:
> * Upon a CPU_DEAD notification, just like the code originally did, we free
>   the kernel's copy of the microcode and invalidate it. So no changes here.
>  
> Bringing a CPU online:
> * When a CPU_ONLINE or CPU_ONLINE_FROZEN notification is received, 
>   a. If the userspace is not frozen, we request microcode from userspace and
>      apply it to the cpu.
> 
>   b. However if we find that the userspace is frozen at that moment, we defer
>      applying microcode now and register a callback function to be executed
>      immediately when the userspace gets thawed. This callback function would
>      request microcode from userspace and apply it to the cpu.

No need for that if we can drop the whole re-requesting of ucode on
CPU_ONLINE* (see my other mail). Let me run some tests before though.

Thanks.

-- 
Regards/Gruss,
Boris.
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