Re: [PATCH v2 1/3] jump_label: Add static_key_fast_inc()

[Peter Zijlstra]

On Thu, Nov 03, 2022 at 09:25:22PM +0000, Dmitry Safonov wrote:
> A helper to add another user for an existing enabled static key.

Utter lack of clue what for.

> +/***
> + * static_key_fast_inc - adds a user for a static key
> + * @key: static key that must be already enabled
> + *
> + * The caller must make sure that the static key can't get disabled while
> + * in this function. It doesn't patch jump labels, only adds a user to
> + * an already enabled static key.
> + */
> +static inline void static_key_fast_inc(struct static_key *key)
> +{
> +	STATIC_KEY_CHECK_USE(key);
> +	WARN_ON_ONCE(atomic_read(&key->enabled) < 1);
> +	atomic_inc(&key->enabled);
> +}

And no, that's racy as heck. We have things like atomic_inc_not_zero(),
I suggest looking into it.