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

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Date:	Thu, 22 May 2014 23:31:08 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Fri, May 23, 2014 at 02:43:31AM +0530, Srivatsa S. Bhat wrote:
> >> 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.
> >>
> 
> That's not quite true. The existing code already ignores FROZEN for all the cases,
> by ignoring it at the top of the switch-case itself:

No, Tony's right and you got confused:

Before my change, the code did:

	if (action == CPU_POST_DEAD) {
		/* intentionally ignoring frozen here */
		cmci_rediscover();
	}

which is only CPU_POST_DEAD *without* the CPU_TASKS_FROZEN bit.

If I move it in the switch-case, cmci_rediscover() *ignores the FROZEN
bit and gets executed for both:

	CPU_DEAD:
	CPU_DEAD_FROZEN:

because with the FROZEN bit masked out, they're the same.

But we don't want to execute it for the FROZEN bit - look for the other
two tests for CPU_TASKS_FROZEN in mce.c for an example.

So, before we go and change the FROZEN aspect and break things in
strange ways, let's keep the _FROZEN ignore. I certainly don't want to
go down that road and chase why we needed FROZEN or not.

Ok?

-- 
Regards/Gruss,
    Boris.

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