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

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Message-ID: <alpine.LFD.2.00.1004061707250.3487@i5.linux-foundation.org>
Date:	Tue, 6 Apr 2010 17:10:15 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
cc:	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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>,
	sgunderson@...foot.com
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux
 2.6.34-rc3)



On Tue, 6 Apr 2010, Rik van Riel wrote:
> 
> It gets more fun.  It looks like the anon_vma is only
> allocated through anon_vma_alloc() and only handled
> by the functions in rmap.c
> 
> By themselves, all of those functions look alright.

Yes. Very trivially so, in fact.

> However, I think I may have found a possible bug in
> the interplay between anon_vma_prepare() and vma_adjust(),
> across several mprotect invocations.
> 
> Let me explain what I think may be going on in small
> steps, since it is quite subtle (assuming I am right).

Sounds at least possible. Way more likely than any of the "trivially 
obvious" code being buggy, or the SLUB layer suddenly having a serious bug 
that only the new user could trigger.

That said, the code that _really_ confuses me is the stuff that uses 
"anon_vma_clone()". Could you please also explain the code flow of 
vma_adjust() to mere mortals, please?

I suspect Borislav is sleeping. But at least we have a patch for him to 
test when he wakes up ;)

		Linus
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