linux-kernel - Re: [patch 02/10] emm: notifier logic

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Date:	Sun, 6 Apr 2008 23:20:08 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Robin Holt <holt@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch 02/10] emm: notifier logic

On Mon, 7 Apr 2008, Andrea Arcangeli wrote:

> > > My mm_lock solution makes all rcu serialization an unnecessary
> > > overhead so you should remove it like I already did in #v11. If it
> > > wasn't the case, then mm_lock wouldn't be a definitive fix for the
> > > race.
> > 
> > There still could be junk in the cache of one cpu. If you just read the 
> > new pointer but use the earlier content pointed to then you have a 
> > problem.
> 
> There can't be junk, spinlocks provides semantics of proper memory
> barriers, just like rcu, so it's entirely superflous.
> 
> There could be junk only if any of the mmu_notifier_* methods would be
> invoked _outside_ the i_mmap_lock and _outside_ the anon_vma and
> outside the mmap_sem, that is never the case of course.

So we use other locks to perform serialization on the list chains? 
Basically the list chains are protected by either mmap_sem or an rmap 
lock? We need to document that.

In that case we could also add an unregister function.

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