linux-kernel - Re: [PATCH] mm: Fix NULL ptr dereference in __count_immobile

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Date:	Thu, 12 Jan 2012 09:21:05 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...e.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH] mm: Fix NULL ptr dereference in __count_immobile_pages

On Wed 11-01-12 14:34:39, Andrew Morton wrote:
> On Tue, 10 Jan 2012 17:30:22 +0100
> Michal Hocko <mhocko@...e.cz> wrote:
> 
> > This patch fixes the following NULL ptr dereference caused by
> > cat /sys/devices/system/memory/memory0/removable:
> 
> Which is world-readable, I assume?

Right. But considering that we haven't seen any report like that it
seems that the HW is rather rare

> 
> > ...
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5608,6 +5608,17 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
> >  bool is_pageblock_removable_nolock(struct page *page)
> >  {
> >  	struct zone *zone = page_zone(page);
> > +	unsigned long pfn = page_to_pfn(page);
> > +
> > +	/*
> > +	 * We have to be careful here because we are iterating over memory
> > +	 * sections which are not zone aware so we might end up outside of
> > +	 * the zone but still within the section.
> > +	 */
> > +	if (!zone || zone->zone_start_pfn > pfn ||
> > +			zone->zone_start_pfn + zone->spanned_pages <= pfn)
> > +		return false;
> > +
> >  	return __count_immobile_pages(zone, page, 0);
> >  }
> 
> So I propose that we backport it into -stable?

Agreed.

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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