Re: [PATCH mptcp-next 08/14] mptcp: avoid additional indirection in mptcp_listen()

[Mat Martineau <martineau@kernel.org>]

On Mon, 10 Jul 2023, Paolo Abeni wrote:

> We are going to remove the first subflow socket soon, so avoid
> the addictional indirection via at listen() time. Instead call
> directly the recently introduced helper on the first subflow sock.
>
> No functional changes intended.
>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> net/mptcp/protocol.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 00b891f709f7..c5da7a172ee9 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -3759,6 +3759,7 @@ static int mptcp_listen(struct socket *sock, int backlog)
> 	struct mptcp_sock *msk = mptcp_sk(sock->sk);
> 	struct sock *sk = sock->sk;
> 	struct socket *ssock;
> +	struct sock *ssk;
> 	int err;
>
> 	pr_debug("msk=%p", msk);
> @@ -3775,15 +3776,20 @@ static int mptcp_listen(struct socket *sock, int backlog)
> 		goto unlock;
> 	}
>
> +	ssk = msk->first;
> 	inet_sk_state_store(sk, TCP_LISTEN);
> 	sock_set_flag(sk, SOCK_RCU_FREE);
>
> -	err = ssock->ops->listen(ssock, backlog);
> -	inet_sk_state_store(sk, inet_sk_state_load(ssock->sk));
> +	lock_sock(ssk);
> +	err = __inet_listen_sk(ssk, backlog);
> +	release_sock(ssk);
> +	inet_sk_state_store(sk, inet_sk_state_load(ssk));
> +
> 	if (!err) {
> +		WRITE_ONCE(sk->sk_max_ack_backlog, backlog);

This seems like new functionality that isn't mentioned in the commit 
message. Do the changes here expose an issue with making the msk-level 
sk_max_ack_backlog match the subflow, or is this an unrelated fix?

> 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
> -		mptcp_copy_inaddrs(sk, ssock->sk);
> -		mptcp_event_pm_listener(ssock->sk, MPTCP_EVENT_LISTENER_CREATED);
> +		mptcp_copy_inaddrs(sk, ssk);
> +		mptcp_event_pm_listener(ssk, MPTCP_EVENT_LISTENER_CREATED);
> 	}
>
> unlock:
> -- 
> 2.41.0
>
>
>