Re: [PATCH v2] mm: Fix slab->page _count corruption.

[Pravin Shelar]

Hi Christoph,
Can you comment on this patch. I have changed it according to your comments.

Thanks,
Pravin.

On Mon, May 14, 2012 at 3:29 PM, Pravin B Shelar <pshelar@xxxxxxxxxx> wrote:
> On arches that do not support this_cpu_cmpxchg_double slab_lock is used
> to do atomic cmpxchg() on double word which contains page->_count.
> page count can be changed from get_page() or put_page() without taking
> slab_lock. That corrupts page counter.
>
> Following patch fixes it by moving page->_count out of cmpxchg_double
> data. So that slub does no change it while updating slub meta-data in
> struct page.
>
> Reported-by: Amey Bhide <abhide@xxxxxxxxxx>
> Signed-off-by: Pravin B Shelar <pshelar@xxxxxxxxxx>
> ---
>  include/linux/mm_types.h |    8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index dad95bd..5f558dc 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -57,8 +57,16 @@ struct page {
>                };
>
>                union {
> +#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
> +    defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
>                        /* Used for cmpxchg_double in slub */
>                        unsigned long counters;
> +#else
> +                       /* Keep _count separate from slub cmpxchg_double data,
> +                        * As rest of double word is protected by slab_lock
> +                        * but _count is not. */
> +                       unsigned counters;
> +#endif
>
>                        struct {
>
> --
> 1.7.10
>
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