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

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Message-ID: <1270629439.5109.553.camel@twins>
Date:	Wed, 07 Apr 2010 10:37:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	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 Tue, 2010-04-06 at 08:55 -0700, Linus Torvalds wrote:
> I do wonder if "page_lock_anon_vma()" should check the whole 
> "page_mapped()" case _after_ taking the anon_vma lock. Because if the race 
> happens, we're following a anon_vma list that has nothing to do with that 
> page (it's stilla _valid_ list, since we locked the anon_vma, but will it 
> be ok?)
> 
> IOW, what is it that really keeps the anon_vma list reliable _and_ 
> relevant wrt the page? We know we may get a stale anon_vma, are we ok if 
> that anon_vma list doesn't actually have anything to do with the page any 
> more? 

When doing the whole make i_mmap_lock/anon_vma->lock a mutex thing last
week I ran into the same issue and its on my todo list to find out wth
is happening there. 

So yes I think we should move that validation check inside
page_lock_anon_vma().

I'll cook up a patch once I'm done staring at the various funny arch
mmu_gather implementations.
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