[PATCH net-next 05/11] mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets
From: Matthieu Baerts (NGI0)
Date: Wed Aug 12 2026 - 10:59:01 EST
From: Shardul Bankar <shardul.b@xxxxxxxxxxxxxxxxxx>
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.
Add per-event MIB counters covering each MPTCP_RST_EMPTCP use site
that is not already covered by an existing counter, named after the
underlying event or condition rather than the reset action:
MD5SigReset MD5SIG enabled on listener (incompatible)
MPJoinSynAckNoMPJoin SYN/ACK missing MP_JOIN option
MPJoinAckNoMPJoin server-side ACK missing MP_JOIN option
(fallback path, MPJoin required)
MPJoinAckNoCtx server-side ACK with no subflow context
MPJoinNoIdFound MP_JOIN with a valid token but no PM local ID
DssReset data mapping invalid (also fires on
MAPPING_NODSS / EMIDDLEBOX path)
MPJoinNotEstablished JOIN attempted on a not-fully-established msk
MPJoinNoIdFound covers the second half of the no-msk MP_JOIN reset:
the existing MPJoinNoTokenFound (MPTCP_MIB_JOINNOTOKEN) only counts the
missing-token case in subflow_token_join_request(), while a JOIN that
carries a valid token but for which the path manager returns no local
id reaches the same MPTCP_RST_EMPTCP in subflow_check_req() uncounted.
The aggregate MPRstTx/MPRstRx counters are unchanged.
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/511
Signed-off-by: Shardul Bankar <shardul.b@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
net/mptcp/mib.c | 7 +++++++
net/mptcp/mib.h | 7 +++++++
net/mptcp/protocol.c | 1 +
net/mptcp/subflow.c | 10 ++++++++++
4 files changed, 25 insertions(+)
diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index 2569385bab7c..608cb568897c 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -21,14 +21,19 @@ static const struct snmp_mib mptcp_snmp_list[] = {
SNMP_MIB_ITEM("MPFallbackTokenInit", MPTCP_MIB_TOKENFALLBACKINIT),
SNMP_MIB_ITEM("MPTCPRetrans", MPTCP_MIB_RETRANSSEGS),
SNMP_MIB_ITEM("MPJoinNoTokenFound", MPTCP_MIB_JOINNOTOKEN),
+ SNMP_MIB_ITEM("MPJoinNoIdFound", MPTCP_MIB_MPJOINNOIDFOUND),
SNMP_MIB_ITEM("MPJoinSynRx", MPTCP_MIB_JOINSYNRX),
SNMP_MIB_ITEM("MPJoinSynBackupRx", MPTCP_MIB_JOINSYNBACKUPRX),
SNMP_MIB_ITEM("MPJoinSynAckRx", MPTCP_MIB_JOINSYNACKRX),
SNMP_MIB_ITEM("MPJoinSynAckBackupRx", MPTCP_MIB_JOINSYNACKBACKUPRX),
SNMP_MIB_ITEM("MPJoinSynAckHMacFailure", MPTCP_MIB_JOINSYNACKMAC),
+ SNMP_MIB_ITEM("MPJoinSynAckNoMPJoin", MPTCP_MIB_MPJOINSYNACKNOMPJOIN),
SNMP_MIB_ITEM("MPJoinAckRx", MPTCP_MIB_JOINACKRX),
SNMP_MIB_ITEM("MPJoinAckHMacFailure", MPTCP_MIB_JOINACKMAC),
+ SNMP_MIB_ITEM("MPJoinAckNoMPJoin", MPTCP_MIB_MPJOINACKNOMPJOIN),
+ SNMP_MIB_ITEM("MPJoinAckNoCtx", MPTCP_MIB_MPJOINACKNOCTX),
SNMP_MIB_ITEM("MPJoinRejected", MPTCP_MIB_JOINREJECTED),
+ SNMP_MIB_ITEM("MPJoinNotEstablished", MPTCP_MIB_MPJOINNOTESTABLISHED),
SNMP_MIB_ITEM("MPJoinSynTx", MPTCP_MIB_JOINSYNTX),
SNMP_MIB_ITEM("MPJoinSynTxCreatSkErr", MPTCP_MIB_JOINSYNTXCREATSKERR),
SNMP_MIB_ITEM("MPJoinSynTxBindErr", MPTCP_MIB_JOINSYNTXBINDERR),
@@ -81,7 +86,9 @@ static const struct snmp_mib mptcp_snmp_list[] = {
SNMP_MIB_ITEM("Blackhole", MPTCP_MIB_BLACKHOLE),
SNMP_MIB_ITEM("MPCapableDataFallback", MPTCP_MIB_MPCAPABLEDATAFALLBACK),
SNMP_MIB_ITEM("MD5SigFallback", MPTCP_MIB_MD5SIGFALLBACK),
+ SNMP_MIB_ITEM("MD5SigReset", MPTCP_MIB_MD5SIGRESET),
SNMP_MIB_ITEM("DssFallback", MPTCP_MIB_DSSFALLBACK),
+ SNMP_MIB_ITEM("DssReset", MPTCP_MIB_DSSRESET),
SNMP_MIB_ITEM("SimultConnectFallback", MPTCP_MIB_SIMULTCONNFALLBACK),
SNMP_MIB_ITEM("FallbackFailed", MPTCP_MIB_FALLBACKFAILED),
SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 3a3425e258a7..1ebdb55e9534 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -16,14 +16,19 @@ enum linux_mptcp_mib_field {
MPTCP_MIB_TOKENFALLBACKINIT, /* Could not init/allocate token */
MPTCP_MIB_RETRANSSEGS, /* Segments retransmitted at the MPTCP-level */
MPTCP_MIB_JOINNOTOKEN, /* Received MP_JOIN but the token was not found */
+ MPTCP_MIB_MPJOINNOIDFOUND, /* Received MP_JOIN but no local ID was found */
MPTCP_MIB_JOINSYNRX, /* Received a SYN + MP_JOIN */
MPTCP_MIB_JOINSYNBACKUPRX, /* Received a SYN + MP_JOIN + backup flag */
MPTCP_MIB_JOINSYNACKRX, /* Received a SYN/ACK + MP_JOIN */
MPTCP_MIB_JOINSYNACKBACKUPRX, /* Received a SYN/ACK + MP_JOIN + backup flag */
MPTCP_MIB_JOINSYNACKMAC, /* HMAC was wrong on SYN/ACK + MP_JOIN */
+ MPTCP_MIB_MPJOINSYNACKNOMPJOIN, /* MP_RST: missing MP_JOIN in SYN/ACK */
MPTCP_MIB_JOINACKRX, /* Received an ACK + MP_JOIN */
MPTCP_MIB_JOINACKMAC, /* HMAC was wrong on ACK + MP_JOIN */
+ MPTCP_MIB_MPJOINACKNOMPJOIN, /* MP_RST: missing MP_JOIN in ACK */
+ MPTCP_MIB_MPJOINACKNOCTX, /* MP_RST: no subflow context on ACK */
MPTCP_MIB_JOINREJECTED, /* The PM rejected the JOIN request */
+ MPTCP_MIB_MPJOINNOTESTABLISHED, /* MP_RST: JOIN on not-fully-established msk */
MPTCP_MIB_JOINSYNTX, /* Sending a SYN + MP_JOIN */
MPTCP_MIB_JOINSYNTXCREATSKERR, /* Not able to create a socket when sending a SYN + MP_JOIN */
MPTCP_MIB_JOINSYNTXBINDERR, /* Not able to bind() the address when sending a SYN + MP_JOIN */
@@ -84,7 +89,9 @@ enum linux_mptcp_mib_field {
* established packet
*/
MPTCP_MIB_MD5SIGFALLBACK, /* Conflicting TCP option enabled */
+ MPTCP_MIB_MD5SIGRESET, /* MP_RST: MD5SIG enabled on listener */
MPTCP_MIB_DSSFALLBACK, /* Bad or missing DSS */
+ MPTCP_MIB_DSSRESET, /* MP_RST: bad data mapping */
MPTCP_MIB_SIMULTCONNFALLBACK, /* Simultaneous connect */
MPTCP_MIB_FALLBACKFAILED, /* Can't fallback due to msk status */
MPTCP_MIB_WINPROBE, /* MPTCP-level zero window probe */
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 8f074d757743..b474d03620a7 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -4002,6 +4002,7 @@ bool mptcp_finish_join(struct sock *ssk)
/* mptcp socket already closing? */
if (!mptcp_is_fully_established(parent)) {
+ MPTCP_INC_STATS(sock_net(parent), MPTCP_MIB_MPJOINNOTESTABLISHED);
subflow->reset_reason = MPTCP_RST_EMPTCP;
return false;
}
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index e1f20ff8fdb4..af81ad5e699d 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -96,6 +96,7 @@ static struct mptcp_sock *subflow_token_join_request(struct request_sock *req)
local_id = mptcp_pm_get_local_id(msk, (struct sock_common *)req);
if (local_id < 0) {
+ SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPJOINNOIDFOUND);
sock_put((struct sock *)msk);
return NULL;
}
@@ -160,6 +161,7 @@ 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;
}
@@ -563,6 +565,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
u8 hmac[SHA256_DIGEST_SIZE];
if (!(mp_opt.suboptions & OPTION_MPTCP_MPJ_SYNACK)) {
+ MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPJOINSYNACKNOMPJOIN);
subflow->reset_reason = MPTCP_RST_EMPTCP;
goto do_reset;
}
@@ -865,6 +868,12 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
*/
if (!ctx || fallback) {
if (fallback_is_fatal) {
+ if (!ctx)
+ MPTCP_INC_STATS(sock_net(sk),
+ MPTCP_MIB_MPJOINACKNOCTX);
+ else
+ MPTCP_INC_STATS(sock_net(sk),
+ MPTCP_MIB_MPJOINACKNOMPJOIN);
subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
goto dispose_child;
}
@@ -1416,6 +1425,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
* subflow_error_report() will introduce the appropriate barriers
*/
subflow->reset_transient = 0;
+ MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSRESET);
subflow->reset_reason = status == MAPPING_NODSS ?
MPTCP_RST_EMIDDLEBOX :
MPTCP_RST_EMPTCP;
--
2.53.0