linux-kernel - Re: [PATCH] mmu notifiers #v7

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Message-Id: <20080228165608.de7c8ae4.akpm@linux-foundation.org>
Date:	Thu, 28 Feb 2008 16:56:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrea Arcangeli <andrea@...ranet.com>
Cc:	Christoph Lameter <clameter@....com>,
	Jack Steiner <steiner@....com>, Nick Piggin <npiggin@...e.de>,
	Robin Holt <holt@....com>, 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>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [PATCH] mmu notifiers #v7

On Fri, 29 Feb 2008 01:40:01 +0100 Andrea Arcangeli <andrea@...ranet.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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