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

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Message-ID: <20100407072903.GB11220@a1.tnic>
Date:	Wed, 7 Apr 2010 09:29:03 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	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)

From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Tue, Apr 06, 2010 at 04:27:42PM -0700

> No, you're mis-reading the asm. It's again the first iteration, and the 
> code above it is again the end of the loop. And %rax is once more a kernel 
> pointer, not the return value of 'page_referenced_one()'. 
> 
> So it once more is 'anon_vma->head.next' that is crap, but now it's not 
> NULL, it's that very odd 0x002e2e2e002e2e2e pattern (the %r13 has had 0x20 
> subtracted from it, so that LSB of "0x0e" is actually _also_ a 0x2e).

No, maybe I expressed myself wrong (it was late an' all) - I was
basically trying to confirm your assessment that anon_vma->head.next
is crap but the code had changed since I had added the debugging 'if
(!anon_vma->head.next)' and that was the value that was already in %r13
before iterating over the list chain.

Yeah, just a minor nitpick and not that it matters. Nevermind though,
we're on the same page.

-- 
Regards/Gruss,
Boris.
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