linux-kernel - Re: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon

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Message-ID: <20100410215115.GA2599@a1.tnic>
Date:	Sat, 10 Apr 2010 23:51:15 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.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: [PATCH -v2] rmap: make anon_vma_prepare link in all the
 anon_vmas of a mergeable VMA

From: Linus Torvalds <torvalds@...ux-foundation.org>
Date: Sat, Apr 10, 2010 at 02:30:49PM -0700

> On Sat, 10 Apr 2010, Borislav Petkov wrote:
> > 
> > Damn, nope, still no joy :(. It looked like it was fixed but one of the
> > test was to hibernate right after the 3 kvm guests were shut down and I
> > guess the mem freeing pattern kinda hits it where it most hurts.
> 
> Damn, I really hoped that was it. Three independent bugs found and fixed, 
> and still no joy? Oh well.

Yep, I'll redo the testing tomorrow, so that we are sure that even with
the _three_ bugs fixed we still hit the funky list element issue.

> > By the way, do we want to create a new thread - the mailchain is off the
> > screen limits of my netbook :)
> 
> I prefer to keep it in one thread so that they all show up together if I 
> need to, but feel free to start a new one. Not a biggie.

I'll keep the thread then - I didn't know it mattered. Mine was just a
suggestion, nevermind.

> > [  647.492781] BUG: unable to handle kernel NULL pointer dereference at (null)
> > [  647.493001] IP: [<ffffffff810c60a0>] page_referenced+0xee/0x1dc
> 
> Well, it sure is consistent. I'll start to think about what else could go 
> wrong..

Which could mean that even with those issues fixed, the real issue is
yet something else. Because obviously the fixes you throw at it don't
seem to change it - even the traces remain consistent across tests.
And if it is use-after-free case, the funny patterns could be some
shifted SLUB poison values which we happen to "see" through the dangling
pointer...  I dunno.

Hmm.

-- 
Regards/Gruss,
Boris.
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