netdev - Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

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Message-ID: <CANn89iLZUA6S2a=K8GObnS62KK6Jt4B7PsAs7meMFooM8xaTgw@mail.gmail.com>
Date: Thu, 2 Nov 2023 18:19:09 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Mat Martineau <martineau@...nel.org>
Cc: Matthieu Baerts <matttbe@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	mptcp@...ts.linux.dev
Subject: Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

On Mon, Oct 23, 2023 at 10:45 PM Mat Martineau <martineau@...nel.org> wrote:
>
> From: Paolo Abeni <pabeni@...hat.com>
>
> The MPTCP protocol account for the data enqueued on all the subflows
> to the main socket send buffer, while the send buffer auto-tuning
> algorithm set the main socket send buffer size as the max size among
> the subflows.
>
> That causes bad performances when at least one subflow is sndbuf
> limited, e.g. due to very high latency, as the MPTCP scheduler can't
> even fill such buffer.
>
> Change the send-buffer auto-tuning algorithm to compute the main socket
> send buffer size as the sum of all the subflows buffer size.
>
> Reviewed-by: Mat Martineau <martineau@...nel.org>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Mat Martineau <martineau@...nel.org

...

> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index df208666fd19..2b43577f952e 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -421,6 +421,7 @@ static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct soc
>
>  void __mptcp_set_connected(struct sock *sk)
>  {
> +       __mptcp_propagate_sndbuf(sk, mptcp_sk(sk)->first);

->first can be NULL here, according to syzbot.

>         if (sk->sk_state == TCP_SYN_SENT) {
>                 inet_sk_state_store(sk, TCP_ESTABLISHED);
>                 sk->sk_state_change(sk);