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

Matthieu Baerts
2026-04-10T09:10:19Z

Hi Paolo,

On 10/04/2026 11:04, Paolo Abeni 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>
Thank you for this review!

Cheers,
Matt
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