linux-kernel - Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

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Date:	Tue, 6 Apr 2010 09:32:43 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux
 2.6.34-rc3)



On Wed, 7 Apr 2010, Minchan Kim wrote:
> > 
> > I don't think so. That isn't the racy case. We're working with a 
> > anon_vma_chain, so the anonvma is all there.
> 
> But the anon_vma is using for another anon_vma. 

No, that can only happen if somebody has done "anon_vma_free()" on it. And 
nobody does that if the anonvma still has a non-empty'&anon_vma->head'.

So as long as the anon_vma has a anon_vma_chain entry associated with it 
(or a ksm refcount, but that's a separate issue), it's not going to be 
re-allocated for any other use, because it's not going to be free'd.
	
		Linus
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