linux-kernel - Re: [PATCH 1/3] slqb: Do not use DEFINE_PER

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Message-Id: <1253514240.5216.3.camel@penberg-laptop>
Date:	Mon, 21 Sep 2009 09:24:00 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Tejun Heo <tj@...nel.org>
Cc:	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	heiko.carstens@...ibm.com, sachinp@...ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] slqb: Do not use DEFINE_PER_CPU for per-node data

Hi Tejun,

On Mon, 2009-09-21 at 00:55 +0900, Tejun Heo wrote:
> Pekka Enberg wrote:
> > Tejun Heo wrote:
> >> Pekka Enberg wrote:
> >>> On Fri, Sep 18, 2009 at 10:34 PM, Mel Gorman <mel@....ul.ie> wrote:
> >>>> SLQB used a seemingly nice hack to allocate per-node data for the
> >>>> statically
> >>>> initialised caches. Unfortunately, due to some unknown per-cpu
> >>>> optimisation, these regions are being reused by something else as the
> >>>> per-node data is getting randomly scrambled. This patch fixes the
> >>>> problem but it's not fully understood *why* it fixes the problem at the
> >>>> moment.
> >>> Ouch, that sounds bad. I guess it's architecture specific bug as x86
> >>> works ok? Lets CC Tejun.
> >>
> >> Is the corruption being seen on ppc or s390?
> > 
> > On ppc.
> 
> Can you please post full dmesg showing the corruption?  Also, if you
> apply the attached patch, does the added BUG_ON() trigger?

I don't have the affected machines, Sachin and Mel do.

			Pekka

> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 878836c..fb690d2 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -127,7 +127,7 @@ extern int __init pcpu_page_first_chunk(size_t reserved_size,
>   * dynamically allocated. Non-atomic access to the current CPU's
>   * version should probably be combined with get_cpu()/put_cpu().
>   */
> -#define per_cpu_ptr(ptr, cpu)	SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu)))
> +#define per_cpu_ptr(ptr, cpu)	({ BUG_ON(!(ptr)); SHIFT_PERCPU_PTR((ptr), per_cpu_offset((cpu))); })
> 
>  extern void *__alloc_reserved_percpu(size_t size, size_t align);

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