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

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Date:	Sat, 8 Aug 2009 19:53:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ondrej Zary <linux@...nbow-software.org>
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


* 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;

?
	Ingo
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