linux-kernel - Re: x86/mce: machine check warning during poweroff

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Message-ID: <CA+55aFxK5XCh6NCbo9AMvsarS9_A+s0QqV6=vC2O4dgg3vg=Aw@mail.gmail.com>
Date:	Fri, 13 Jan 2012 18:53:04 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Ming Lei <tom.leiming@...il.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	Borislav Petkov <borislav.petkov@....com>,
	Tony Luck <tony.luck@...el.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	gouders@...bocholt.fh-gelsenkirchen.de,
	Marcos Souza <marcos.mage@...il.com>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	prasad@...ux.vnet.ibm.com, justinmattock@...il.com,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>,
	Gilad Ben-Yossef <gilad@...yossef.com>
Subject: Re: x86/mce: machine check warning during poweroff

On Fri, Jan 13, 2012 at 6:41 PM, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>
> YES!! Finally I have a fix for this whole MCE thing! :-)

Goodie.

> The patch below works perfectly for me - I tested multiple CPU hotplug
> operations as well as multiple pm_test runs at core level. Please let me
> know if this solves the suspend issue as well..

Ok, I'll try, and I bet it does.

HOWEVER.

I'd be a whole lot happier knowing exactly which field in "struct
device" that needed to be NULL before it gets registered.

I don't like how

  device_register() + device_create_file(dev)..

is not sufficiently undone by

 .. device_remove_file(dev) +  device_unregister()

so that it can't be repeated. Exactly *what* state is stale and
re-used incorrectly if you do that device_register() a second time.

It smells like a misfeature of the device core handling.

But that does obviously explain why this started happening with a
fairly straightforward conversion from sysdev to struct device. It
just makes me worry about any *other* such conversions.

Of course, normal users will allocate and free the memory, so never
see this "re-use the same piece of memory" issue. But still..

                 Linus
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