linux-kernel - Re: [PATCH 07/11] Memory compaction core

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Message-Id: <20100324141400.72479ce6.akpm@linux-foundation.org>
Date:	Wed, 24 Mar 2010 14:14:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jonathan Corbet <corbet@....net>
Cc:	Mel Gorman <mel@....ul.ie>, Andrea Arcangeli <aarcange@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 07/11] Memory compaction core

On Wed, 24 Mar 2010 14:59:46 -0600
Jonathan Corbet <corbet@....net> wrote:

> On Wed, 24 Mar 2010 13:33:47 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > > +	VM_BUG_ON(cc == NULL);  
> > 
> > It's a bit strange to test this when we're about to oops anyway.  The
> > oops will tell us the same thing.
> 
> ...except that we've seen a fair number of null pointer dereference
> exploits that have told us something altogether different.  Are we
> *sure* we don't want to test for null pointers...?
> 

It's hard to see what the test gains us really - the kernel has
zillions of pointer derefs, any of which could be NULL if we have a
bug.  Are we more likely to have a bug here than elsewhere?

This one will oops on a plain old read, so it's a bit moot in this
case.
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