linux-kernel - Re: [PATCH] OOPS in identify

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Date:	Sat, 8 Aug 2009 20:19:20 +0200
From:	Ondrej Zary <linux@...nbow-software.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] OOPS in identify_cpu() on CPUs without CPUID

On Saturday 08 August 2009 19:53:44 Ingo Molnar wrote:
> * Ondrej Zary <linux@...nbow-software.org> wrote:
> > Kernel is broken for x86 CPUs without CPUID since 2.6.28. It
> > crashes with NULL pointer dereference in identify_cpu():
> >
> > 766        generic_identify(c);
> > 767
> > 768-->     if (this_cpu->c_identify)
> > 769                this_cpu->c_identify(c);
> >
> > this_cpu is NULL. This is because it's only initialized in
> > get_cpu_vendor() function, which is not called if the CPU has no
> > CPUID instruction.
>
> indeed ...
>
> > Signed-off-by: Ondrej Zary <linux@...nbow-software.org>
> >
> > --- linux-2.6.30.4-orig/arch/x86/kernel/cpu/common.c	2009-06-10
> > 05:05:27.000000000 +0200 +++
> > linux-2.6.30.4-router/arch/x86/kernel/cpu/common.c	2009-08-08
> > 18:00:21.000000000 +0200 @@ -699,6 +699,7 @@
> >
> >  static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
> >  {
> > +	this_cpu = &default_cpu;
> >  	c->extended_cpuid_level = 0;
> >
> >  	if (!have_cpuid_p())
>
> How about initializing this_cpu instead, via:
>
> static const struct cpu_dev *this_cpu __cpuinitdata = &default_cpu;
>
> ?

That might be even better - looks cleaner. I can't test it right now as I 
don't have the hardware here. I'll test it tomorrow (unless someone will be 
faster).

-- 
Ondrej Zary
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