linux-kernel - Re: [PATCH] x86, MCE: Kill CPU_POST

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Date:	Thu, 22 May 2014 21:55:38 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...nel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"ego@...ux.vnet.ibm.com" <ego@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] x86, MCE: Kill CPU_POST_DEAD

On Thu, May 22, 2014 at 03:50:21PM +0000, Luck, Tony wrote:
> >> So I think we can reduce it to just the one rwsem (with recursion) if we
> >> shoot CPU_POST_DEAD in the head.
> >
> > Here's the first bullet. Stressing my box here with Steve's hotplug
> > script seems to work fine.
> >
> > Tony, any objections?
> 
> what was this comment referring to:
> 
>     /* intentionally ignoring frozen here */
> 
> After you move the cmci_rediscover() call, it is now in a place where we are
> no longer ignoring frozen (i.e. the old placement did the rediscover even if the
> CPU_TASKS_FROZEN bit was set - with the new placement we will skip rediscovery.
>
> So we were working around some interaction between cpu hotplug and frozen.
> Do we no longer need to do that?

Hmm, that FROZEN thing is supposedly for hotplug operations while
suspend is happening. I guess it makes a little sense to rediscover CMCI
banks while suspend is in progress. Whatever.

Let's keep it before more crap ensues, that was a good catch, thanks.

So, I guess something like that instead.

Which means, I'd need to run a couple of suspend/resume rounds while
hotplugging cores to see whether we're still kosher.

More fun tomorrow.

---
From: Borislav Petkov <bp@...e.de>
Date: Thu, 22 May 2014 16:40:54 +0200
Subject: [PATCH] x86, MCE: Kill CPU_POST_DEAD

In conjunction with cleaning up CPU hotplug, we want to get rid of
CPU_POST_DEAD. Kill this instance here and rediscover CMCI banks at the
end of CPU_DEAD.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 68317c80de7f..bfde4871848f 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -2391,6 +2391,10 @@ mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 			threshold_cpu_callback(action, cpu);
 		mce_device_remove(cpu);
 		mce_intel_hcpu_update(cpu);
+
+		/* intentionally ignoring frozen here */
+		if (!(action & CPU_TASKS_FROZEN))
+			cmci_rediscover();
 		break;
 	case CPU_DOWN_PREPARE:
 		smp_call_function_single(cpu, mce_disable_cpu, &action, 1);
@@ -2402,11 +2406,6 @@ mce_cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 		break;
 	}
 
-	if (action == CPU_POST_DEAD) {
-		/* intentionally ignoring frozen here */
-		cmci_rediscover();
-	}
-
 	return NOTIFY_OK;
 }
 
-- 
1.9.0


-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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