On Fri, 2025-09-19 at 17:53 +0200, Paolo Abeni wrote:
> MPTCP currently generate a dummy data_fin for fallback socket
> when the fallback subflow has completed data reception using
> the current ack_seq.
>
> We are going to introduce backlog usage for the msk soon, even
> for fallback sockets: the ack_seq value will not match the most
> recent
> sequence number seen by the fallback subflow socket, as it will
> ignore
> data_seq sitting in the backlog.
>
> Instead use the last map sequence number to set the data_fin,
> as fallback (dummy) map sequences are always in sequence.
>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
LGTM.
Reviewed-by: Geliang Tang <geliang@kernel.org>
Tested-by: Geliang Tang <geliang@kernel.org>
Thanks,
-Geliang
> ---
> v2 -> v3:
> - keep the close check in subflow_sched_work_if_closed, fix
> CI failures
> ---
> net/mptcp/subflow.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index e8325890a3223..b9455c04e8a46 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -1285,6 +1285,7 @@ static bool subflow_is_done(const struct sock
> *sk)
> /* sched mptcp worker for subflow cleanup if no more data is pending
> */
> static void subflow_sched_work_if_closed(struct mptcp_sock *msk,
> struct sock *ssk)
> {
> + const struct mptcp_subflow_context *subflow =
> mptcp_subflow_ctx(ssk);
> struct sock *sk = (struct sock *)msk;
>
> if (likely(ssk->sk_state != TCP_CLOSE &&
> @@ -1303,7 +1304,8 @@ static void subflow_sched_work_if_closed(struct
> mptcp_sock *msk, struct sock *ss
> */
> if (__mptcp_check_fallback(msk) && subflow_is_done(ssk) &&
> msk->first == ssk &&
> - mptcp_update_rcv_data_fin(msk, READ_ONCE(msk->ack_seq),
> true))
> + mptcp_update_rcv_data_fin(msk, subflow->map_seq +
> + subflow->map_data_len, true))
> mptcp_schedule_work(sk);
> }
>