Re: [PATCH 1/2] lkdtm: use atomic_t to replace count_lock

[Arnd Bergmann <arnd@arndb.de>]

On Thursday 02 February 2012, Cong Wang wrote:
> > In order to have an atomic here, you have to use a loop around
> > atomic_cmpxchg, like
> >
> >
> >       int old, new;
> >       old = atomic_read(&count);
> >       do {
> >               new = old ? old - 1 : cpoint_count;
> >               old = cmpxchg(&count, old, new);
> >       } while (old != new);
> >
> > I suppose you could also just keep the spinlock and move lkdtm_do_action()
> > outside of it?
> 
> If we still need spinlock, I think we don't need to bother atomic_t at all.

Yes, it's one or the other: If you use the cmpxchg loop, you don't need a
spinlock and vice versa.

	Arnd