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

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Message-ID: <4AB6508C.4070602@kernel.org>
Date:	Mon, 21 Sep 2009 00:55:56 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
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

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?

Thanks.

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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