[ofa-general] Re: [PATCH] mmu notifiers #v7

[Andrew Morton]

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