Re: [PATCH mptcp-net v3 1/2] mptcp: sync the msk->sndbuf at accept() time

Paolo Abeni
2026-04-10T09:04:34Z

On 4/7/26 10:45 AM, Gang Yan wrote:
> From: Gang Yan <yangang@kylinos.cn>
>
> After an MPTCP connection is established, the sk_sndbuf of client's msk
> can be updated through 'subflow_finish_connect'. However, the newly
> accepted msk on the server side has a small sk_sndbuf than
> msk->first->sk_sndbuf:
>
> '''
> MPTCP: msk:00000000e55b09db, msk->sndbuf:20480, msk->first->sndbuf:2626560
> '''
>
> This patch synchronizes the sk_sndbuf by triggering its update during
> accept.

I finally could wrap my head around the root cause: tcp_child_process()
-> tcp_init_transfer() -> tcp_sndbuf_expand() can and will grow the ssk
sndbuf _after_ tcp_check_req() -> subflow_syn_recv_sock() ->
mptcp_sk_clone_init() where __mptcp_propagate_sndbuf() is currently hooked.

I think the latter __mptcp_propagate_sndbuf() invocation can be removed,
and the commit message expanded to capture some of the above.

With the above included feel free to add:

Acked-by: Paolo Abeni <pabeni@redhat.com>