linux-kernel - Re: [PATCH x86/percpu] x86_64: initialize this_cpu_off to __per_cpu

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Date:	Fri, 16 Jan 2009 14:16:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <htejun@...il.com>
Cc:	roel kluin <roel.kluin@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	ebiederm@...ssion.com, cl@...ux-foundation.org,
	rusty@...tcorp.com.au, travis@....com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	steiner@....com, hugh@...itas.com
Subject: Re: [PATCH x86/percpu] x86_64: initialize this_cpu_off to
	__per_cpu_load


* Tejun Heo <htejun@...il.com> wrote:

> On x86_64, if get_per_cpu_var() is used before per cpu area is setup
> (if lockdep is turned on, it happens), it needs this_cpu_off to point
> to __per_cpu_load.  Initialize accordingly.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
> Okay, this fixes the problem.  Tested with gcc-4.3.2 and binutils-2.19
> (openSUSE 11.1).  For all four variants I can test (64-smp, 64-up,
> 32-smp, 32-up).  This and the previous merge fix patch are available
> in the following git branch.

cool!

>   git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git tj-percpu
> 
>  arch/x86/kernel/smpcommon.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/smpcommon.c b/arch/x86/kernel/smpcommon.c
> index 84395fa..7e15781 100644
> --- a/arch/x86/kernel/smpcommon.c
> +++ b/arch/x86/kernel/smpcommon.c
> @@ -3,8 +3,13 @@
>   */
>  #include <linux/module.h>
>  #include <asm/smp.h>
> +#include <asm/sections.h>
>  
> +#ifdef CONFIG_X86_64
> +DEFINE_PER_CPU(unsigned long, this_cpu_off) = (unsigned long)__per_cpu_load;
> +#else
>  DEFINE_PER_CPU(unsigned long, this_cpu_off);
> +#endif

I've pulled your tree, but couldnt we do this symmetrically in the 32-bit 
case too and avoid the ugly #ifdef somehow?

	Ingo
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