linux-kernel - Re: [patch 1/6] mmu

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Message-ID: <Pine.LNX.4.64.0802051017520.11705@schroedinger.engr.sgi.com>
Date:	Tue, 5 Feb 2008 10:19:29 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andy Whitcroft <apw@...dowen.org>
cc:	Andrea Arcangeli <andrea@...ranet.com>, Robin Holt <holt@....com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	Nick Piggin <npiggin@...e.de>, kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 1/6] mmu_notifier: Core code

On Tue, 5 Feb 2008, Andy Whitcroft wrote:

> > +	if (unlikely(!hlist_empty(&mm->mmu_notifier.head))) {
> > +		rcu_read_lock();
> > +		hlist_for_each_entry_safe_rcu(mn, n, t,
> > +					  &mm->mmu_notifier.head, hlist) {
> > +			if (mn->ops->release)
> > +				mn->ops->release(mn, mm);
> 
> Does this ->release actually release the 'nm' and its associated hlist?
> I see in this thread that this ordering is deemed "use after free" which
> implies so.

Right that was fixed in a later release and discussed extensively later. 
See V5.

> I am not sure it makes sense to add a _safe_rcu variant.  As I understand
> things an _safe variant is used where we are going to remove the current

It was dropped in V5.

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