linux-kernel - Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related operation to happen

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Message-ID: <20080425192532.GA19717@sgi.com>
Date:	Fri, 25 Apr 2008 14:25:32 -0500
From:	Robin Holt <holt@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Lameter <clameter@....com>,
	akpm@...ux-foundation.org, Nick Piggin <npiggin@...e.de>,
	Steve Wise <swise@...ngridcomputing.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	Robin Holt <holt@....com>, general@...ts.openfabrics.org,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH 1 of 9] Lock the entire mm to prevent any mmu related
	operation to happen

On Fri, Apr 25, 2008 at 06:56:40PM +0200, Andrea Arcangeli wrote:
> Fortunately I figured out we don't really need mm_lock in unregister
> because it's ok to unregister in the middle of the range_begin/end
> critical section (that's definitely not ok for register that's why
> register needs mm_lock). And it's perfectly ok to fail in register().

I think you still need mm_lock (unless I miss something).  What happens
when one callout is scanning mmu_notifier_invalidate_range_start() and
you unlink.  That list next pointer with LIST_POISON1 which is a really
bad address for the processor to track.

Maybe I misunderstood your description.

Thanks,
Robin
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