Re: [PATCH] x86/refcount: Implement fast refcount_t handling

Peter Zijlstra
2017-04-24T10:46:20Z

On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote:
> +static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
> +{
> + const int a = 1;
> + const int u = 0;
> + int c, old;
> +
> + c = atomic_read(&(r->refs));
> + for (;;) {
> + if (unlikely(c == (u)))
> + break;
> + old = atomic_cmpxchg(&(r->refs), c, c + (a));

Please use atomic_try_cmpxchg(), that generates saner code.

> + if (likely(old == c))
> + break;
> + c = old;
> + }
> + return c != u;
> +}