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

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Date:	Fri, 7 Oct 2011 00:34:38 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Borislav Petkov <bp@...64.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Borislav Petkov <bp@...en8.de>,
	"tigran@...azian.fsnet.co.uk" <tigran@...azian.fsnet.co.uk>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...e.hu" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [BUGFIX][PATCH RESEND] Freezer, CPU hotplug, x86 Microcode: Fix
 task freezing failures

On Thu, Oct 06, 2011 at 06:13:34PM -0400, Tejun Heo wrote:
> Hello,
> 
> On Fri, Oct 07, 2011 at 02:05:49AM +0530, Srivatsa S. Bhat wrote:
> ...
> > diff --git a/arch/x86/kernel/microcode_core.c b/arch/x86/kernel/microcode_core.c
> > index f924280..cd7ef2f 100644
> > --- a/arch/x86/kernel/microcode_core.c
> > +++ b/arch/x86/kernel/microcode_core.c
> > @@ -483,7 +483,15 @@ mc_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
> >  		sysfs_remove_group(&sys_dev->kobj, &mc_attr_group);
> >  		pr_debug("CPU%d removed\n", cpu);
> >  		break;
> > -	case CPU_DEAD:
> > +
> > +	/*
> > +	 * Do not invalidate the microcode if a CPU goes offline,
> > +	 * because it would be impossible to get the microcode again
> > +	 * from userspace when the CPU comes back up, if the userspace
> > +	 * happens to be frozen at that moment by the freezer subsystem,
> > +	 * for example, due to a suspend operation in progress.
> > +	 */
> > +
> 
> This still looks like a bandaid to me.  The exclusion approach didn't
> pan out?

Well, this saves us the needless reloading of the ucode image when the
CPU comes back online and is an annoyance fix and onlining path speedup
in its own right. I, as you, thought that the exclusion approach should
be the proper fix. Srivatsa?

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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