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

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Date:	Tue, 7 Apr 2009 21:31:45 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andi Kleen <andi@...stfloor.org>, 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 09:03:30PM +0200, Johannes Weiner wrote:
> 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

It won't free it then. Later on it will take it out of the free lists,
but that code is not written yet.

> (!page_count()) then the get_page() in memory_failure() will trigger a
> VM_BUG.  So either this check is unneeded or it should be

So no bug
> get_page_unless_zero() in memory_failure()?

That's not what this is handling.  The issue is that sometimes
the process can still freeing it and we need to make sure it 
never hits the free lists.

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