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

[Peter Zijlstra]

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.