* [PATCH v4 1/2] mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets
2026-06-11 20:32 [PATCH v4 0/2] mptcp: per-event MIB counters for MPTCP_RST_EMPTCP Shardul Bankar
@ 2026-06-11 20:32 ` Shardul Bankar
2026-06-11 20:32 ` [PATCH v4 2/2] selftests: mptcp: check per-event MPTCP_RST_EMPTCP counters Shardul Bankar
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Shardul Bankar @ 2026-06-11 20:32 UTC (permalink / raw)
To: mptcp
Cc: Matthieu Baerts, Mat Martineau, Geliang Tang, pabeni, kalpan.jani,
janak, shardulsb08, Shardul Bankar
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@mpiricsoftware.com>
---
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 d9bd4f4afcc0e..a43893456a2e8 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 18f35f7e0a2d4..18bcd8c749adc 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 a4f7e99b30dbc..3e035f368038a 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3976,6 +3976,7 @@ 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 8e386899ceb98..6e8932f5c9ed0 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;
}
@@ -568,6 +570,7 @@ 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;
}
@@ -870,6 +873,12 @@ 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;
}
@@ -1421,6 +1430,7 @@ 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;
--
2.34.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH v4 2/2] selftests: mptcp: check per-event MPTCP_RST_EMPTCP counters
2026-06-11 20:32 [PATCH v4 0/2] mptcp: per-event MIB counters for MPTCP_RST_EMPTCP Shardul Bankar
2026-06-11 20:32 ` [PATCH v4 1/2] mptcp: add per-event MIB counters for MPTCP_RST_EMPTCP resets Shardul Bankar
@ 2026-06-11 20:32 ` Shardul Bankar
2026-06-11 21:34 ` [PATCH v4 0/2] mptcp: per-event MIB counters for MPTCP_RST_EMPTCP MPTCP CI
2026-08-07 17:56 ` Matthieu Baerts
3 siblings, 0 replies; 5+ messages in thread
From: Shardul Bankar @ 2026-06-11 20:32 UTC (permalink / raw)
To: mptcp
Cc: Matthieu Baerts, Mat Martineau, Geliang Tang, pabeni, kalpan.jani,
janak, shardulsb08, Shardul Bankar
Add named env-var expectations for each per-event MPTCP_RST_EMPTCP
counter, matching the pattern used by the existing JOIN/RST checks.
Each defaults to 0 and is checked silently on success; a mismatch prints
a check line and fails the test. Counters absent from the running
kernel are skipped silently so older kernels do not false-fail.
The JOIN-related counters (MPJoinSynAckNoMPJoin, MPJoinAckNoMPJoin,
MPJoinAckNoCtx, MPJoinNotEstablished, MPJoinNoIdFound) are checked in
chk_join_nr() on fixed namespaces; the two remaining reset counters
(MD5SigReset, DssReset) stay in chk_rst_nr().
Add a test at the end of signal_address_tests that triggers
MPJoinSynAckNoMPJoin: ns1 signals an address that is already bound on
the client (ns2), where a TCP-only mptcp_connect listener is started.
The client's MP_JOIN routes locally to the TCP listener, which responds
with a plain SYN/ACK without the MP_JOIN option, and the new counter
increments on the client side.
Other per-event counters (MD5SigReset, MPJoinAckNoMPJoin, MPJoinAckNoCtx,
DssReset, MPJoinNotEstablished, MPJoinNoIdFound) are not currently
reachable from mptcp_join.sh; the env-var hooks are in place for future
tests to set expectations explicitly.
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
---
.../testing/selftests/net/mptcp/mptcp_join.sh | 93 +++++++++++++++++++
1 file changed, 93 insertions(+)
diff --git a/tools/testing/selftests/net/mptcp/mptcp_join.sh b/tools/testing/selftests/net/mptcp/mptcp_join.sh
index 550a6b6117a98..25768e700067c 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_join.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_join.sh
@@ -75,6 +75,14 @@ unset join_syn_tx
unset join_create_err
unset join_bind_err
unset join_connect_err
+unset join_synack_no_mpjoin
+unset join_ack_no_mpjoin
+unset join_ack_no_ctx
+unset join_not_established
+unset join_no_id_found
+
+unset rst_md5sig
+unset rst_dss
unset fb_ns1
unset fb_ns2
@@ -1353,6 +1361,8 @@ chk_rst_nr()
local rst_tx=$1
local rst_rx=$2
local ns_invert=${3:-""}
+ local md5sig=${rst_md5sig:-0}
+ local dss=${rst_dss:-0}
local count
local ns_tx=$ns1
local ns_rx=$ns2
@@ -1389,6 +1399,21 @@ chk_rst_nr()
else
print_ok
fi
+
+ # MPTCP_RST_EMPTCP reset-event counters; default 0, gated on
+ # availability. Fixed namespaces: MD5SigReset fires on the listener
+ # (server), DssReset on the data receiver (client).
+ count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMD5SigReset")
+ if [ -n "$count" ] && [ "$count" != "$md5sig" ]; then
+ print_check "MD5SigReset"
+ fail_test "got $count MD5SigReset expected $md5sig"
+ fi
+
+ count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtDssReset")
+ if [ -n "$count" ] && [ "$count" != "$dss" ]; then
+ print_check "DssReset"
+ fail_test "got $count DssReset expected $dss"
+ fi
}
chk_infi_nr()
@@ -1587,6 +1612,11 @@ chk_join_nr()
local rst_nr=${join_rst_nr:-0}
local infi_nr=${join_infi_nr:-0}
local corrupted_pkts=${join_corrupted_pkts:-0}
+ local synack_no_mpjoin=${join_synack_no_mpjoin:-0}
+ local ack_no_mpjoin=${join_ack_no_mpjoin:-0}
+ local ack_no_ctx=${join_ack_no_ctx:-0}
+ local not_established=${join_not_established:-0}
+ local no_id_found=${join_no_id_found:-0}
local rc=${KSFT_PASS}
local count
local with_cookie
@@ -1655,6 +1685,44 @@ chk_join_nr()
fail_test "got $count JOIN[s] syn rejected expected $syn_rej"
fi
+ # Per-event MPTCP_RST_EMPTCP JOIN counters; default 0, gated on
+ # availability. Fixed namespaces: the *SynAck* one fires on the
+ # client receiving the SYN/ACK, the others on the server.
+ count=$(mptcp_lib_get_counter ${ns2} "MPTcpExtMPJoinSynAckNoMPJoin")
+ if [ -n "$count" ] && [ "$count" != "$synack_no_mpjoin" ]; then
+ rc=${KSFT_FAIL}
+ print_check "synack no mpjoin"
+ fail_test "got $count JOIN[s] synack no mpjoin expected $synack_no_mpjoin"
+ fi
+
+ count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinAckNoMPJoin")
+ if [ -n "$count" ] && [ "$count" != "$ack_no_mpjoin" ]; then
+ rc=${KSFT_FAIL}
+ print_check "ack no mpjoin"
+ fail_test "got $count JOIN[s] ack no mpjoin expected $ack_no_mpjoin"
+ fi
+
+ count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinAckNoCtx")
+ if [ -n "$count" ] && [ "$count" != "$ack_no_ctx" ]; then
+ rc=${KSFT_FAIL}
+ print_check "ack no ctx"
+ fail_test "got $count JOIN[s] ack no ctx expected $ack_no_ctx"
+ fi
+
+ count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinNotEstablished")
+ if [ -n "$count" ] && [ "$count" != "$not_established" ]; then
+ rc=${KSFT_FAIL}
+ print_check "join not established"
+ fail_test "got $count JOIN[s] not established expected $not_established"
+ fi
+
+ count=$(mptcp_lib_get_counter ${ns1} "MPTcpExtMPJoinNoIdFound")
+ if [ -n "$count" ] && [ "$count" != "$no_id_found" ]; then
+ rc=${KSFT_FAIL}
+ print_check "join no id found"
+ fail_test "got $count JOIN[s] no id found expected $no_id_found"
+ fi
+
print_results "join Rx" ${rc}
join_syn_tx="${join_syn_tx:-${syn_nr}}" \
@@ -2359,6 +2427,31 @@ signal_address_tests()
chk_add_nr 4 4
fi
fi
+
+ # signalled address belongs to the client, where a TCP-only
+ # listener is bound at it: the client's MP_JOIN routes locally
+ # to the listener and receives a SYN/ACK without MP_JOIN.
+ # MPJoinSynAckNoMPJoin increments on the client side.
+ if reset "signal address, TCP-only listener on client"; then
+ local extra_bind
+ local port
+
+ pm_nl_set_limits $ns1 0 1
+ pm_nl_set_limits $ns2 1 1
+ pm_nl_add_endpoint $ns1 10.0.2.2 flags signal
+
+ port=$(get_port)
+ ip netns exec ${ns2} ./mptcp_connect -l -t -1 -p "$port" \
+ -s TCP 10.0.2.2 &
+ extra_bind=$!
+ mptcp_lib_wait_local_port_listen "$ns2" "$port"
+
+ run_tests $ns1 $ns2 10.0.1.1
+ join_synack_no_mpjoin=1 join_syn_tx=1 \
+ chk_join_nr 0 0 0
+
+ kill ${extra_bind} 2>/dev/null
+ fi
}
laminar_endp_tests()
--
2.34.1
^ permalink raw reply related [flat|nested] 5+ messages in thread