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

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Message-ID: <20111006221334.GB7085@google.com>
Date:	Thu, 6 Oct 2011 15:13:34 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	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

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?

Thank you.

-- 
tejun
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