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References: <20221123173859.473629-1-dima@arista.com> <20221123173859.473629-4-dima@arista.com>
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From:   Eric Dumazet <edumazet@google.com>
Date:   Thu, 1 Dec 2022 20:38:44 +0100
Message-ID: <CANn89iJEYhTFsF8vqe6enE7d107HfXZvgxN=iLGQj21sx9gwcQ@mail.gmail.com>
Subject: Re: [PATCH v6 3/5] net/tcp: Disable TCP-MD5 static key on
 tcp_md5sig_info destruction
To:     Dmitry Safonov <dima@arista.com>
Cc:     linux-kernel@vger.kernel.org, David Ahern <dsahern@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Bob Gilligan <gilligan@arista.com>,
        "David S. Miller" <davem@davemloft.net>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Francesco Ruggeri <fruggeri@arista.com>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Jason Baron <jbaron@akamai.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Salam Noureddine <noureddine@arista.com>,
        Steven Rostedt <rostedt@goodmis.org>, netdev@vger.kernel.org
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On Wed, Nov 23, 2022 at 6:39 PM Dmitry Safonov <dima@arista.com> wrote:
>
> To do that, separate two scenarios:
> - where it's the first MD5 key on the system, which means that enabling
>   of the static key may need to sleep;
> - copying of an existing key from a listening socket to the request
>   socket upon receiving a signed TCP segment, where static key was
>   already enabled (when the key was added to the listening socket).
>
> Now the life-time of the static branch for TCP-MD5 is until:
> - last tcp_md5sig_info is destroyed
> - last socket in time-wait state with MD5 key is closed.
>
> Which means that after all sockets with TCP-MD5 keys are gone, the
> system gets back the performance of disabled md5-key static branch.
>
> While at here, provide static_key_fast_inc() helper that does ref
> counter increment in atomic fashion (without grabbing cpus_read_lock()
> on CONFIG_JUMP_LABEL=y). This is needed to add a new user for
> a static_key when the caller controls the lifetime of another user.
>
> Signed-off-by: Dmitry Safonov <dima@arista.com>
> Acked-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Eric Dumazet <edumazet@google.com>