Re: [PATCH v3 1/2] mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets

[Matthieu Baerts <matttbe@kernel.org>]

Hi Shardul,

On 12/05/2026 20:33, Shardul Bankar wrote:
> MPTCP_RST_EMPTCP (reset reason 1) is used as a catch-all for several
> distinct error conditions across subflow setup, authentication, and
> data-path validation.  The existing MPRstTx/MPRstRx counters only
> track aggregate reset volume, making it difficult to diagnose which
> code path is triggering subflow resets in production.

(...)

> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index d562e149606f6..6fce3f431667c 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -160,6 +160,7 @@ static int subflow_check_req(struct request_sock *req,
>  	 * TCP option space.
>  	 */
>  	if (rcu_access_pointer(tcp_sk(sk_listener)->md5sig_info)) {
> +		MPTCP_INC_STATS(sock_net(sk_listener), MPTCP_MIB_MD5SIGRESET);
>  		subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
>  		return -EINVAL;
>  	}

In the v1, you also had another counter added in this helper, for the
MPJOIN case with !subflow_req->msk: I thought that JOINNOTOKEN was
always sent in this case. I just noticed another possible error that
could come from the PM side if there is no local_id. I don't know if we
should cover this case, but maybe "safer" to?

Maybe adding a MPJoinNoIdFound and use it in subflow_token_join_request,
similar to MPJoinNoTokenFound?

Cheers,
Matt
-- 
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