linux-kernel - Re: BUG() on apm resume in 2.6.18-rc2

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Date:	Thu, 27 Jul 2006 00:08:56 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Johannes Weiner <hnazfoo@...glemail.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG() on apm resume in 2.6.18-rc2

On Thu, 27 Jul 2006 08:29:32 +0200
Johannes Weiner <hnazfoo@...glemail.com> wrote:

> Hi,
> 
> On Wed, Jul 26, 2006 at 11:10:49PM -0700, Andrew Morton wrote:
> > This?
> > 
> > --- a/./arch/i386/kernel/cpu/mcheck/mce.h~mce-section-fix
> > +++ a/./arch/i386/kernel/cpu/mcheck/mce.h
> > @@ -9,6 +9,6 @@ void winchip_mcheck_init(struct cpuinfo_
> >  /* Call the installed machine check handler for this CPU setup. */
> >  extern fastcall void (*machine_check_vector)(struct pt_regs *, long error_code);
> >  
> > -extern int mce_disabled __initdata;
> > +extern int mce_disabled;
> >  extern int nr_mce_banks;
> 
> What hinted you to that? I didn't read much oopses, so...
> 

(please always do reply-to-all)

That was an easy one - it crashed at

EIP is at mcheck_init+0x4/0x80

right at the start of mcheck_init(), so it had to be the access of
mce_disabled.

It accessed the address c0729c38:

BUG: unable to handle kernel paging request at virtual address c0729c38

and the code dump shows an access to that address.

And the only way in which an access to a global variable of this nature can
oops is if that variable has been unmapped from the kenrel address space. 
We unmap (and reuse) the __init memory, so it had to be a sectioning bug.
-
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