linux-kernel - Re: [PATCH v5 1/5] jump_label: Prevent key->enabled int overflow

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Message-ID: <Y33w1z01l9EerNwu@hirez.programming.kicks-ass.net>
Date:   Wed, 23 Nov 2022 11:07:19 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org, David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Bob Gilligan <gilligan@...sta.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Francesco Ruggeri <fruggeri@...sta.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Salam Noureddine <noureddine@...sta.com>,
        Steven Rostedt <rostedt@...dmis.org>, netdev@...r.kernel.org
Subject: Re: [PATCH v5 1/5] jump_label: Prevent key->enabled int overflow

On Tue, Nov 22, 2022 at 06:55:30PM +0000, Dmitry Safonov wrote:

> key->enabled is indeed a ref-counter as it's documented in multiple
> places: top comment in jump_label.h, Documentation/staging/static-keys.rst,
> etc.

> +/***
> + * static_key_fast_inc_not_negative - 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.
> + *
> + * Returns true if the increment was done.
> + */

One more thing; it might be useful to point out that unlike refcount_t
this thing does not saturate but will fail to increment on overflow.