netdev - Re: [PATCH v2 1/3] jump_label: Add static_key_fast

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Message-ID: <89d05f19-ca8e-7906-e3ca-973225d8300f@arista.com>
Date:   Fri, 4 Nov 2022 16:27:13 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        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>,
        Paolo Abeni <pabeni@...hat.com>,
        Salam Noureddine <noureddine@...sta.com>,
        netdev@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 1/3] jump_label: Add static_key_fast_inc()

On 11/3/22 21:41, Peter Zijlstra wrote:
> 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.

Thanks for the review, I'll look into that for v3.

Thanks,
          Dmitry