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

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Date:	Wed, 07 Apr 2010 00:34:55 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Tue, 2010-04-06 at 10:38 -0400, Rik van Riel wrote:
> On 04/06/2010 04:53 AM, KOSAKI Motohiro wrote:
> 
> > Today, I've reviewed this patch carefully. but I haven't found any bug.
> 
> > Also, I've runned stress workload with shrink_all_memory() today. but
> > I couldn't reproduce the issue. hmm..  (perhaps I'm no lucky guy.
> > I'm frequently fail to reproduce)
> >
> > I'll continue to work.
> 
> My status with this bug is the same - I have gone through
> the code from all angles, but have not found any other bugs
> yet (except for that leak - which could leave invalid
> pointers behind).

Let's see the unlink_anon_vmas. 

1. list_for_each_entry_safe(avc,next, vma->anon_vma_chain, same_vma)
2. 	anon_vma_unlink
3. 		spin_lock(anon_vma->lock) <-- HERE LOCK.
4.		list_del(anon_vma_chain->same_anon_vma);

What if anon_vma is destroyed and reuse by SLAB_XXX_RCU for another
anon_vma object between 2 and 3?
I mean how to make sure 3) does lock valid anon_vma? 

I hope it is culprit.


-- 
Kind regards,
Minchan Kim


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