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

gang.yan
2026-04-11T03:51:20Z

April 10, 2026 at 5:04 PM, "Paolo Abeni" <pabeni@redhat.com mailto:pabeni@redhat.com?to=%22Paolo%20Abeni%22%20%3Cpabeni%40redhat.com%3E > wrote:

>
> 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>
Hi Paolo,

Thanks for your suggestions. The v4 code will be sent soon.

Cherrs,
Gang
>