Re: [PATCH] mmu notifiers #v7

Andrew Morton
2008-02-29T01:07:50Z

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.