linux-kernel - Re: [PATCH] [8/16] POISON: Add various poison checks in mm/memory.c

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Date:	Tue, 7 Apr 2009 21:03:30 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH] [8/16] POISON: Add various poison checks in mm/memory.c

On Tue, Apr 07, 2009 at 05:10:05PM +0200, Andi Kleen wrote:
> 
> Bail out early when poisoned pages are found in page fault handling.
> Since they are poisoned they should not be mapped freshly
> into processes.
> 
> This is generally handled in the same way as OOM, just a different
> error code is returned to the architecture code.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> 
> ---
>  mm/memory.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> Index: linux/mm/memory.c
> ===================================================================
> --- linux.orig/mm/memory.c	2009-04-07 16:39:39.000000000 +0200
> +++ linux/mm/memory.c	2009-04-07 16:39:39.000000000 +0200
> @@ -2560,6 +2560,10 @@
>  		goto oom;
>  	__SetPageUptodate(page);
>  
> +	/* Kludge for now until we take poisoned pages out of the free lists */
> +	if (unlikely(PagePoison(page)))
> +		return VM_FAULT_POISON;
> +

When memory_failure() hits a page still on the free list
(!page_count()) then the get_page() in memory_failure() will trigger a
VM_BUG.  So either this check is unneeded or it should be
get_page_unless_zero() in memory_failure()?
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