Re: [PATCH v6 3/5] net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction

[Eric Dumazet]

On Wed, Nov 23, 2022 at 6:39 PM Dmitry Safonov <dima@xxxxxxxxxx> 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@xxxxxxxxxx>
> Acked-by: Jakub Kicinski <kuba@xxxxxxxxxx>

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>