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 09:28:58 -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:
> > 
> > However, that made me look at the PAGE_MIGRATION case. That seems to be 
> > just broken. It's doing that page_anon_vma() + spin_lock without holding 
> > any RCU locks, so there is no guarantee that anon_vma there is at all 
> > valid.
> 
> FYI, recently there is a patch about migration case. 
> http://lkml.org/lkml/2010/4/2/145

No, I'm talking about rmap_walk_anon():

        anon_vma = page_anon_vma(page);
        if (!anon_vma)
                return ret;
        spin_lock(&anon_vma->lock);

which seems to be simply buggy. The anon_vma may not exist any more, 
because an RCU event might have really freed the page between looking it 
up and locking it.

			Linus
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