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

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Date:	Mon, 2 Jul 2012 20:46:12 -0300
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Pravin B Shelar <pshelar@...ira.com>,
	Amey Bhide <abhide@...ira.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [ 07/48] mm: fix slab->page _count corruption when using slub

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@...ira.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@...ux-foundation.org: use standard comment layout, tweak comment text]
> Reported-by: Amey Bhide <abhide@...ira.com>
> Signed-off-by: Pravin B Shelar <pshelar@...ira.com>
> Acked-by: Christoph Lameter <cl@...ux.com>
> Cc: Pekka Enberg <penberg@...helsinki.fi>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Ben Hutchings <ben@...adent.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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