Date: Tue, 6 Apr 2010 09:28:58 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Minchan Kim <minchan.kim@gmail.com>
cc: Rik van Riel <riel@redhat.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Borislav Petkov <bp@alien8.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
       Nick Piggin <npiggin@suse.de>, Andrea Arcangeli <aarcange@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux
 2.6.34-rc3)
In-Reply-To: <1270571019.1814.163.camel@barrios-desktop>
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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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