Re: [PATCH 5/6] lib/refcount: Improve performance of generic REFCOUNT_FULL code

[Will Deacon]

On Fri, Aug 02, 2019 at 08:55:14PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 02, 2019 at 11:09:59AM +0100, Will Deacon wrote:
> >  static inline void refcount_add(int i, refcount_t *r)
> >  {
> > +	int old = atomic_fetch_add_relaxed(i, &r->refs);
> > +
> > +	WARN_ONCE(!old, "refcount_t: addition on 0; use-after-free.\n");
> > +	if (unlikely(old <= 0 || old + i <= 0)) {
> > +		refcount_set(r, REFCOUNT_SATURATED);
> > +		WARN_ONCE(1, "refcount_t: saturated; leaking memory.\n");
> > +	}
> >  }
> 
> That will trigger both WARNs when !old.

Right you are. I'll make the second WARN_ONCE(old, ...);

Will