From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Thu, 28 Feb 2008 16:56:08 -0800
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mmu notifiers #v7
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To: Andrea Arcangeli <andrea@qumranet.com>
Cc: Christoph Lameter <clameter@sgi.com>, Jack Steiner <steiner@sgi.com>, Nick Piggin <npiggin@suse.de>, Robin Holt <holt@sgi.com>, Avi Kivity <avi@qumranet.com>, Izik Eidus <izike@qumranet.com>, kvm-devel@lists.sourceforge.net, Peter Zijlstra <a.p.zijlstra@chello.nl>, general@lists.openfabrics.org, Steve Wise <swise@opengridcomputing.com>, Roland Dreier <rdreier@cisco.com>, Kanoj Sarcar <kanojsarcar@yahoo.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com
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On Fri, 29 Feb 2008 01:40:01 +0100 Andrea Arcangeli <andrea@qumranet.com> wrote:

> > > +#define mmu_notifier(function, mm, args...)				\
> > > +	do {								\
> > > +		struct mmu_notifier *__mn;				\
> > > +		struct hlist_node *__n;					\
> > > +									\
> > > +		if (unlikely(!hlist_empty(&(mm)->mmu_notifier.head))) { \
> > > +			rcu_read_lock();				\
> > > +			hlist_for_each_entry_rcu(__mn, __n,		\
> > > +						 &(mm)->mmu_notifier.head, \
> > > +						 hlist)			\
> > > +				if (__mn->ops->function)		\
> > > +					__mn->ops->function(__mn,	\
> > > +							    mm,		\
> > > +							    args);	\
> > > +			rcu_read_unlock();				\
> > > +		}							\
> > > +	} while (0)
> > 
> > Andrew recomended local variables for parameters used multile times. This 
> > means the mm parameter here.
> 
> I don't exactly see what "buggy macro" meant?

multiple refernces to the argument, so

	mmu_notifier(foo, bar(), zot);

will call bar() either once or twice.

Unlikely in this case, but bad practice.  Easily fixable by using another
temporary.

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