linux-kernel - Re: EMM: disable other notifiers before register and unregister

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Message-ID: <Pine.LNX.4.64.0804031215050.7480@schroedinger.engr.sgi.com>
Date:	Thu, 3 Apr 2008 12:20:41 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Hugh Dickins <hugh@...itas.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Nick Piggin <npiggin@...e.de>
Subject: Re: EMM: disable other notifiers before register and unregister

On Thu, 3 Apr 2008, Andrea Arcangeli wrote:

> My attempt to fix this once and for all is to walk all vmas of the
> "mm" inside mmu_notifier_register and take all anon_vma locks and
> i_mmap_locks in virtual address order in a row. It's ok to take those
> inside the mmap_sem. Supposedly if anybody will ever take a double
> lock it'll do in order too. Then I can dump all the other locking and

What about concurrent mmu_notifier registrations from two mm_structs 
that have shared mappings? Isnt there a potential deadlock situation?

> faults). So it should be ok to take all those locks inside the
> mmap_sem and implement a lock_vm(mm) unlock_vm(mm). I'll think more
> about this hammer approach while I try to implement it...

Well good luck. Hopefully we will get to something that works.

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