linux-kernel - Re: [PATCH 2/2] mm: Fix slab->page

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Date:	Mon, 14 May 2012 13:58:59 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Pravin B Shelar <pshelar@...ira.com>
cc:	penberg@...nel.org, mpm@...enic.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, jesse@...ira.com, abhide@...ira.com
Subject: Re: [PATCH 2/2] mm: Fix slab->page _count corruption.

On Mon, 14 May 2012, Pravin B Shelar 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.

Ugly. Maybe its best to not touch the count in the page lock case in slub?

You could accomplish that by changing the definition of counters in
mm_types.h. Make it unsigned instead of unsigned long so that it only
covers the first part of the struct (which excludes the refcounter)


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