linux-kernel - Re: [PATCH] mmu notifiers #v6

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Message-ID: <20080220153409.GA7128@v2.random>
Date:	Wed, 20 Feb 2008 16:34:09 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Robin Holt <holt@....com>
Cc:	Nick Piggin <npiggin@...e.de>, akpm@...ux-foundation.org,
	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, Christoph Lameter <clameter@....com>
Subject: Re: [PATCH] mmu notifiers #v6

On Wed, Feb 20, 2008 at 08:41:55AM -0600, Robin Holt wrote:
> On Wed, Feb 20, 2008 at 11:39:42AM +0100, Andrea Arcangeli wrote:
> > XPMEM simply can't use RCU for the registration locking if it wants to
> > schedule inside the mmu notifier calls. So I guess it's better to add
> 
> Whoa there.  In Christoph's patch, we did not use rcu for the list.  It
> was a simple hlist_head.  The list manipulations were done under
> down_write(&current->mm->mmap_sem) and would therefore not be racy.  All
> the callout locations are already acquiring the mmap_sem at least
> readably, so we should be safe.  Maybe I missed a race somewhere.

You missed quite a few, see when atomic=1 and when mmu_rmap_notifier
is invoked for example.
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