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

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Message-ID: <4BBB55DC.8070509@redhat.com>
Date:	Tue, 06 Apr 2010 11:40:12 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Minchan Kim <minchan.kim@...il.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 04/06/2010 11:34 AM, Minchan Kim wrote:

> 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.

How can the anon_vma get destroyed and reused, when this
anon_vma_chain still has a reference to it (and the
anon_vma has not been freed yet)?

What combination of circumstances is necessary for
your bug hypothetical to happen?
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