linux-kernel - Re: [PATCH] Use correct page frame number to grab page zone lock

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Message-ID: <4908A392.1060401@austin.ibm.com>
Date:	Wed, 29 Oct 2008 12:55:30 -0500
From:	Nathan Fontenot <nfont@...tin.ibm.com>
To:	linux-kernel@...r.kernel.org
CC:	Badari Pulavarty <badari@...ibm.com>
Subject: Re: [PATCH] Use correct page frame number to grab page zone lock

Disregard.  It appears that Gerald Schaefer submitted a patch to fix
this already.

http://lkml.org/lkml/2008/10/29/142

-Nathan

Nathan Fontenot wrote:
> There are situations in which the 'pfn' variable used to calculate the
> page zone can be invalid.  One case is in the hotplug memory remove path
> where we are trying to remove memory the last valid page frame for the
> system.  Passing an invalid page frame number to the pfn_to_page() macro
> will cause the system to oops.
> 
> Additionally I think this also solves an issue where we may be grabbing
> the wrong zone->lock.  This would occur when 'pfn' refers to a page
> frame beyond what we are examining and lies in a different zone.
> 
> Using the starting page frame number passed in appears to resolve
> both of these issues.  This patch also removes the redundant
> initialization of 'pfn', it is set explicitly and then again in the for 
> loop.
> 
> 
> Signed-off-by: Nathan Fontenot <nfont@...tin.ibm.com>
> ---
> 
> Index: linux-2.6/mm/page_isolation.c
> ===================================================================
> --- linux-2.6.orig/mm/page_isolation.c    2008-10-13 12:00:46.000000000 
> -0500
> +++ linux-2.6/mm/page_isolation.c    2008-10-29 11:18:39.000000000 -0500
> @@ -119,7 +119,6 @@
>     struct zone *zone;
>     int ret;
> 
> -    pfn = start_pfn;
>     /*
>      * Note: pageblock_nr_page != MAX_ORDER. Then, chunks of free page
>      * is not aligned to pageblock_nr_pages.
> @@ -133,7 +132,7 @@
>     if (pfn < end_pfn)
>         return -EBUSY;
>     /* Check all pages are free or Marked as ISOLATED */
> -    zone = page_zone(pfn_to_page(pfn));
> +    zone = page_zone(pfn_to_page(start_pfn));
>     spin_lock_irqsave(&zone->lock, flags);
>     ret = __test_page_isolated_in_pageblock(start_pfn, end_pfn);
>     spin_unlock_irqrestore(&zone->lock, flags);
> -- 
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