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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 13 Jan 2012 18:53:04 -0800
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Subject: Re: x86/mce: machine check warning during poweroff
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Ming Lei <tom.leiming@gmail.com>, Djalal Harouni <tixxdz@opendz.org>,
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On Fri, Jan 13, 2012 at 6:41 PM, Srivatsa S. Bhat
<srivatsa.bhat@linux.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