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

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

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;
> +}