Re: [PATCH 1/3] slqb: Do not use DEFINE_PER_CPU for per-node data

[Tejun Heo <tj@kernel.org>]

Pekka Enberg wrote:
> Tejun Heo wrote:
>> Pekka Enberg wrote:
>>> On Fri, Sep 18, 2009 at 10:34 PM, Mel Gorman <mel@csn.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);