linux-kernel - Re: [PATCH] [6/16] HWPOISON: Add various poison checks in mm/memory.c

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Date:	Thu, 4 Jun 2009 07:19:15 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] [6/16] HWPOISON: Add various poison checks in mm/memory.c

On Thu, Jun 04, 2009 at 12:26:03PM +0800, Wu Fengguang wrote:
> On Thu, Jun 04, 2009 at 02:46:38AM +0800, Andi Kleen wrote:
> > 
> > Bail out early when hardware poisoned pages are found in page fault handling.
> 
> I suspect this patch is also not absolutely necessary: the poisoned
> page will normally have been isolated already.

It's needed to prevent new pages comming in when there is a parallel 
fault while the memory failure handling is in process.
Otherwise the pages could get remapped in that small window.

> > --- linux.orig/mm/memory.c	2009-06-03 19:36:23.000000000 +0200
> > +++ linux/mm/memory.c	2009-06-03 19:36:23.000000000 +0200
> > @@ -2797,6 +2797,9 @@
> >  	if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
> >  		return ret;
> >  
> > +	if (unlikely(PageHWPoison(vmf.page)))
> > +		return VM_FAULT_HWPOISON;
> > +
> 
> Direct return with locked page could lockup someone later.
> Either drop this patch or fix it with this check?

Fair point. Fixed. 

Thanks,
-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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