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

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Date:	Fri, 13 Jan 2012 15:02:01 -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>
Subject: Re: x86/mce: machine check warning during poweroff

On Fri, Jan 13, 2012 at 12:22 PM, Srivatsa S. Bhat
<srivatsa.bhat@...ux.vnet.ibm.com> wrote:
>
> Fundamentally, this warning is triggered during CPU Offline, which is done
> during poweroff, suspend, hibernate etc. IOW, even a simple
> # echo 0 > /sys/devices/system/cpu/cpuX/online will trigger it.

There is definitely something wrong with CPU hotplug and MCE.

I seem to be able to trigger not only warnings, but some oopses, by doing:

 - enable list debugging, slab debugging, and kobject debugging in the
kernel (I've got some other things enabled too, but I think those are
the main ones)

 - do

     echo 0 > /sys/devices/system/cpu/cpuX/online

   this gets a few warnings

 - then do

     echo 1 > /sys/devices/system/cpu/cpuX/online

where bringing it up again will crash the machine entirely.

The oops scrolled off the screen an ddidn't get caught anywhere, but
the call trace seems to be (warning: hand-entered, so some of this may
be bogus):

Oops in:
  kobject_get+0x10/0x40

Code:
  55 48 89 f8 48 89 e5 48 83 ec 10 48 85 ff 74 0b <8b> 57 38 85 d2 74 06 f0 ff

Call trace:
  get_device
  klist_device_get
  klist_add_tail
  bus_add_device
  device_add
  device_register
  mce_device_create
  notifier_call_chain
  __raw_notifier_call_chain
  __cpu_notify
  _cpu_up
  store_online
  dev_attr_change
  sysfs_write_file

so it's definitely something bad in MCE device handling, and probably
something to do with reusing a 'struct device' after freeign it, or
after not having completely cleaned it up.

I didn't see if I could spot the problem, but I think this is entirely
reproducible, so hopefully somebody who knows the MCE code can
trivially see this and fix it.

                   Linus
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