Re: [ 07/48] mm: fix slab->page _count corruption when using slub

Herton Ronaldo Krzesinski
2012-07-02T23:46:22Z

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On Sun, Jul 01, 2012 at 06:20:13PM +0100, Ben Hutchings wrote:
> 3.2-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Pravin B Shelar <pshelar@nicira.com>
>
> commit abca7c4965845924f65d40e0aa1092bdd895e314 upstream.
>
> 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. The
> page count can be changed from get_page() or put_page() without taking
> slab_lock. That corrupts page counter.
>
> Fix 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.

Hi,

I got a frozen machine on boot with 3.2.22 proposed patches, bisect
pointed out to this commit (and reverting only this commit on top of
3.2.22 patches confirmed it). So far I was able to reproduce always.

Only happened with an x86_64 kernel, gzipped config attached. Using
earlyprintk=vga, I'm able to see the boot process is stuck just right
after "Memory: ...k available..." message (right before SLUB prints
its initialization message).

>
> [akpm@linux-foundation.org: use standard comment layout, tweak comment text]
> Reported-by: Amey Bhide <abhide@nicira.com>
> Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
> Acked-by: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@cs.helsinki.fi>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
> include/linux/mm_types.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index dad95bd..704a626 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -57,8 +57,18 @@ 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 the rest of the double word is protected by
> + * slab_lock but _count is not.
> + */
> + unsigned counters;
> +#endif
>
> struct {
>
>
>
> --
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[]'s
Herton

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