Optimize subscr_conns lookup

It was found that, on a busy osmo-bsc (>1000 concurrent calls spread over
several BTS), the CPU consumption looking up for gsm_subscriber_conn
based on SCCP conn_id can take a considerable amount of time (>5% of
osmo-bsc already taking 70% of the CPU time on the core it is running on).

The huge CPU consumption happens because a linear search is done (llist)
over the entire list of SCCP connections every time an SCCP message is
handled.

In order to optimize this lookup, this patch introduces a new struct
bsc_sccp_inst which becomes associated to the libosmo-sccp
osmo_sccp_instance. Each of this strucs maintains an rbtree of
gsm_subscriber_conn ordered by conn_id.
As a result algorithmic complexity adds O(log(N)) during insert, lookup
and delete of SCCP conns, but gets rid of O(N) previous lookup.
As a plus, finding a new conn_id now takes generally O(log(N)), while
before it used to take O(N).

Related: SYS#6200
Change-Id: I667d3ec1dad0ab7bc0fa4799d9611f3a914d07e5

TODO-RELEASE

@@ -12,3 +12,4 @@
 		osmo-bsc CTRL,VTY	osmo_fsm instance IDs now use new dynamic timeslot names 'DYNAMIC_OSMOCOM' and 'DYNAMIC_IPACCESS'
 libosmogsm	>1.8.0		circuit switched data stuff (gsm0808_enc/dec_channel_type etc.)
 libosmo-abis	>1.4.0		osmo_ortp.h: add RTP_PT_CSDATA
+libosmo-sccp >1.7.0		osmo_sccp_{get,set}_priv()

include/osmocom/bsc/gsm_data.h

@@ -19,6 +19,8 @@
 #include <osmocom/core/fsm.h>
 #include <osmocom/core/tdef.h>
 #include <osmocom/core/time_cc.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/linuxrbtree.h>
 
 #include <osmocom/crypt/auth.h>
 
@@ -331,6 +333,9 @@ struct gsm_subscriber_connection {
 		/* SCCP connection related */
 		struct bsc_msc_data *msc;
 
+		/* entry in (struct bsc_sccp_inst)->connections */
+		struct rb_node node;
+
 		/* Sigtran connection ID:
 		*  if set: Range (0..SCCP_CONN_ID_MAX) (24 bit)
 		*  if unset: SCCP_CONN_ID_UNSET (-1) if unset */
@@ -871,6 +876,19 @@ struct all_allocated {
 	struct osmo_time_cc static_tch;
 };
 
+struct bsc_sccp_inst {
+	struct osmo_sccp_instance *sccp; /* backpointer */
+	/* rbtree root of 'sstruct gsm_subscriber_connection' in this instance, ordered by conn_id */
+	struct rb_root connections;
+	uint32_t next_id; /* next id to allocate */
+};
+
+struct bsc_sccp_inst *bsc_sccp_inst_alloc(void *ctx);
+uint32_t bsc_sccp_inst_next_conn_id(struct bsc_sccp_inst *bsc_sccp);
+int bsc_sccp_inst_register_gscon(struct bsc_sccp_inst *bsc_sccp, struct gsm_subscriber_connection *conn);
+void bsc_sccp_inst_unregister_gscon(struct bsc_sccp_inst *bsc_sccp, struct gsm_subscriber_connection *conn);
+struct gsm_subscriber_connection *bsc_sccp_inst_get_gscon_by_conn_id(const struct bsc_sccp_inst *bsc_sccp, uint32_t conn_id);
+
 struct gsm_network {
 	struct osmo_plmn_id plmn;
 
@@ -1030,8 +1048,6 @@ enum gsm_phys_chan_config gsm_pchan_by_lchan_type(enum gsm_chan_t type);
 enum gsm48_rr_cause bsc_gsm48_rr_cause_from_gsm0808_cause(enum gsm0808_cause c);
 enum gsm48_rr_cause bsc_gsm48_rr_cause_from_rsl_cause(uint8_t c);
 
-uint32_t bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp);
-
 /* Interference Measurement Parameters */
 struct gsm_interf_meas_params {
 	/* Intave: Interference Averaging period (see 3GPP TS 45.008, table A.1) */

src/osmo-bsc/bsc_sccp.c

@@ -27,11 +27,82 @@
 #include <osmocom/bsc/bsc_msc_data.h>
 #include <osmocom/bsc/lb.h>
 
-/* We need an unused SCCP conn_id across all SCCP users. */
+struct bsc_sccp_inst *bsc_sccp_inst_alloc(void *ctx)
-uint32_t bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp)
 {
-	static uint32_t next_id = 1;
+	struct bsc_sccp_inst *bsc_sccp;
-	int i;
+
+	bsc_sccp = talloc_zero(ctx, struct bsc_sccp_inst);
+	OSMO_ASSERT(bsc_sccp);
+	bsc_sccp->next_id = 1;
+
+	return bsc_sccp;
+}
+
+int bsc_sccp_inst_register_gscon(struct bsc_sccp_inst *bsc_sccp, struct gsm_subscriber_connection *conn)
+{
+	struct rb_node **n = &(bsc_sccp->connections.rb_node);
+	struct rb_node *parent = NULL;
+	uint32_t conn_id = conn->sccp.conn_id;
+
+	OSMO_ASSERT(conn_id != SCCP_CONN_ID_UNSET);
+
+	while (*n) {
+		struct gsm_subscriber_connection *it;
+
+		it = container_of(*n, struct gsm_subscriber_connection, sccp.node);
+
+		parent = *n;
+		if (conn_id < it->sccp.conn_id) {
+			n = &((*n)->rb_left);
+		} else if (conn_id > it->sccp.conn_id) {
+			n = &((*n)->rb_right);
+		} else {
+			LOGP(DMSC, LOGL_ERROR,
+			     "Trying to reserve already reserved conn_id %u\n", conn_id);
+			return -EEXIST;
+		}
+	}
+
+	rb_link_node(&conn->sccp.node, parent, n);
+	rb_insert_color(&conn->sccp.node, &bsc_sccp->connections);
+	return 0;
+}
+
+void bsc_sccp_inst_unregister_gscon(struct bsc_sccp_inst *bsc_sccp, struct gsm_subscriber_connection *conn)
+{
+	OSMO_ASSERT(conn->sccp.conn_id != SCCP_CONN_ID_UNSET);
+	rb_erase(&conn->sccp.node, &bsc_sccp->connections);
+}
+
+/* Helper function to Check if the given connection id is already assigned */
+struct gsm_subscriber_connection *bsc_sccp_inst_get_gscon_by_conn_id(const struct bsc_sccp_inst *bsc_sccp, uint32_t conn_id)
+{
+	const struct rb_node *node = bsc_sccp->connections.rb_node;
+	struct gsm_subscriber_connection *conn;
+
+	OSMO_ASSERT(conn_id != SCCP_CONN_ID_UNSET);
+	/* Range (0..SCCP_CONN_ID_MAX) expected, see bsc_sccp_inst_next_conn_id() */
+	OSMO_ASSERT(conn_id <= SCCP_CONN_ID_MAX);
+
+	while (node) {
+		conn = container_of(node, struct gsm_subscriber_connection, sccp.node);
+		if (conn_id < conn->sccp.conn_id)
+			node = node->rb_left;
+		else if (conn_id > conn->sccp.conn_id)
+			node = node->rb_right;
+		else
+			return conn;
+	}
+
+	return NULL;
+}
+
+/* We need an unused SCCP conn_id across all SCCP users. */
+uint32_t bsc_sccp_inst_next_conn_id(struct bsc_sccp_inst *bsc_sccp)
+{
+	uint32_t first_id, test_id;
+
+	first_id = test_id = bsc_sccp->next_id;
 
 	/* SUA: RFC3868 sec 3.10.4:
 	*    The source reference number is a 4 octet long integer.
@@ -41,59 +112,26 @@ uint32_t bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp)
 	*    reference number which is generated and used by the local node to identify the
 	*    connection section after the connection section is set up.
 	*    The coding "all ones" is reserved for future use.
-	* Hence, let's simply use 24 bit ids to fit all link types (excluding 0x00ffffff).
+	*Hence, as we currently use the connection ID also as local reference,
+	*let's simply use 24 bit ids to fit all link types (excluding 0x00ffffff).
 	*/
 
-	/* This looks really suboptimal, but in most cases the static next_id should indicate exactly the next unused
+	while (bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, test_id)) {
-	 * conn_id, and we only iterate all conns once to make super sure that it is not already in use. */
-
-	/* SCCP towards SMLC: */
-	if (bsc_gsmnet->smlc->sccp == sccp) {
-		for (i = 0; i < SCCP_CONN_ID_MAX; i++) {
-			struct gsm_subscriber_connection *conn;
-			uint32_t conn_id = next_id;
-			bool conn_id_already_used = false;
-
-			/* Optimized modulo operation (% SCCP_CONN_ID_MAX) using bitwise AND plus CMP: */
-			next_id = (next_id + 1) & 0x00FFFFFF;
-			if (OSMO_UNLIKELY(next_id == 0x00FFFFFF))
-				next_id = 0;
-
-			llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
-				if (conn->lcs.lb.state != SUBSCR_SCCP_ST_NONE &&
-				    conn->lcs.lb.conn_id == conn_id) {
-					conn_id_already_used = true;
-					break;
-				}
-			}
-
-			if (!conn_id_already_used)
-				return conn_id;
-		}
-		return 0xFFFFFFFF;
-	}
-
-	/* SCCP towards MSC: */
-	for (i = 0; i < SCCP_CONN_ID_MAX; i++) {
-		struct gsm_subscriber_connection *conn;
-		uint32_t conn_id = next_id;
-		bool conn_id_already_used = false;
-
 		/* Optimized modulo operation (% SCCP_CONN_ID_MAX) using bitwise AND plus CMP: */
-		next_id = (next_id + 1) & 0x00FFFFFF;
+		test_id = (test_id + 1) & 0x00FFFFFF;
-		if (OSMO_UNLIKELY(next_id == 0x00FFFFFF))
+		if (OSMO_UNLIKELY(test_id == 0x00FFFFFF))
-			next_id = 0;
+			test_id = 0;
 
-		llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
+		/* Did a whole loop, all used, fail */
-			if (conn->sccp.msc && conn->sccp.msc->a.sccp == sccp &&
+		if (OSMO_UNLIKELY(test_id == first_id))
-			    conn->sccp.conn_id == conn_id) {
+			return SCCP_CONN_ID_UNSET;
-				conn_id_already_used = true;
-				break;
-			}
-		}
-
-		if (!conn_id_already_used)
-			return conn_id;
 	}
-	return SCCP_CONN_ID_UNSET;
+
+	bsc_sccp->next_id = test_id;
+	/* Optimized modulo operation (% SCCP_CONN_ID_MAX) using bitwise AND plus CMP: */
+	bsc_sccp->next_id = (bsc_sccp->next_id + 1) & 0x00FFFFFF;
+	if (OSMO_UNLIKELY(bsc_sccp->next_id == 0x00FFFFFF))
+		bsc_sccp->next_id = 0;
+
+	return test_id;
 }

src/osmo-bsc/bsc_subscr_conn_fsm.c

@@ -1111,6 +1111,11 @@ static void gscon_cleanup(struct osmo_fsm_inst *fi, enum osmo_fsm_term_cause cau
 		osmo_sccp_tx_disconn(msc->a.sccp_user, conn->sccp.conn_id, &msc->a.bsc_addr, 0);
 		conn->sccp.state = SUBSCR_SCCP_ST_NONE;
 	}
+	if (conn->sccp.conn_id != SCCP_CONN_ID_UNSET && conn->sccp.msc) {
+		struct bsc_sccp_inst *bsc_sccp = osmo_sccp_get_priv(conn->sccp.msc->a.sccp);
+		bsc_sccp_inst_unregister_gscon(bsc_sccp, conn);
+		conn->sccp.conn_id = SCCP_CONN_ID_UNSET;
+	}
 
 	if (conn->bsub) {
 		LOGPFSML(fi, LOGL_DEBUG, "Putting bsc_subscr\n");

src/osmo-bsc/lb.c

@@ -31,22 +31,7 @@
 #include <osmocom/bsc/osmo_bsc_sigtran.h>
 #include <osmocom/bsc/lcs_loc_req.h>
 #include <osmocom/bsc/bssmap_reset.h>
-
+#include <osmocom/bsc/gsm_data.h>
-static struct gsm_subscriber_connection *get_bsc_conn_by_lb_conn_id(uint32_t conn_id)
-{
-	struct gsm_subscriber_connection *conn;
-
-	/* Range (0..SCCP_CONN_ID_MAX) expected, see bsc_sccp_inst_next_conn_id() */
-	OSMO_ASSERT(conn_id <= SCCP_CONN_ID_MAX);
-
-	llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
-		if (conn->lcs.lb.state != SUBSCR_SCCP_ST_NONE
-		    && conn->lcs.lb.conn_id == conn_id)
-			return conn;
-	}
-
-	return NULL;
-}
 
 /* Send reset to SMLC */
 int bssmap_le_tx_reset(void)
@@ -150,6 +135,8 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 {
 	struct osmo_scu_prim *scu_prim = (struct osmo_scu_prim *)oph;
 	struct osmo_sccp_user *scu = _scu;
+	struct osmo_sccp_instance *sccp = osmo_sccp_get_sccp(scu);
+	struct bsc_sccp_inst *bsc_sccp = osmo_sccp_get_priv(sccp);
 	struct gsm_subscriber_connection *conn;
 	int rc = 0;
 
@@ -172,7 +159,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 	case OSMO_PRIM(OSMO_SCU_PRIM_N_CONNECT, PRIM_OP_CONFIRM):
 		/* Handle inbound confirmation of outbound connection */
 		DEBUGP(DLCS, "N-CONNECT.cnf(%u)\n", scu_prim->u.connect.conn_id);
-		conn = get_bsc_conn_by_lb_conn_id(scu_prim->u.connect.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.connect.conn_id);
 		if (conn) {
 			conn->lcs.lb.state = SUBSCR_SCCP_ST_CONNECTED;
 			if (msgb_l2len(oph->msg) > 0) {
@@ -188,7 +175,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		/* Handle incoming connection oriented data */
 		DEBUGP(DLCS, "N-DATA.ind(%u)\n", scu_prim->u.data.conn_id);
 
-		conn = get_bsc_conn_by_lb_conn_id(scu_prim->u.data.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.data.conn_id);
 		if (!conn) {
 			LOGP(DLCS, LOGL_ERROR, "N-DATA.ind(%u) for unknown conn_id\n", scu_prim->u.data.conn_id);
 			rc = -EINVAL;
@@ -206,7 +193,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)),
 		       scu_prim->u.disconnect.cause);
 		/* indication of disconnect */
-		conn = get_bsc_conn_by_lb_conn_id(scu_prim->u.disconnect.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.disconnect.conn_id);
 		if (!conn) {
 			LOGP(DLCS, LOGL_ERROR, "N-DISCONNECT.ind for unknown conn_id %u\n",
 			     scu_prim->u.disconnect.conn_id);
@@ -234,6 +221,7 @@ static int lb_open_conn(struct gsm_subscriber_connection *conn, struct msgb *msg
 	struct osmo_ss7_instance *ss7;
 	uint32_t conn_id;
 	int rc;
+	struct bsc_sccp_inst *bsc_sccp = osmo_sccp_get_priv(bsc_gsmnet->smlc->sccp);
 
 	OSMO_ASSERT(conn);
 	OSMO_ASSERT(msg);
@@ -244,7 +232,7 @@ static int lb_open_conn(struct gsm_subscriber_connection *conn, struct msgb *msg
 		return -EINVAL;
 	}
 
-	conn_id = bsc_sccp_inst_next_conn_id(bsc_gsmnet->smlc->sccp);
+	conn_id = bsc_sccp_inst_next_conn_id(bsc_sccp);
 	if (conn_id == SCCP_CONN_ID_UNSET) {
 		LOGPFSMSL(conn->fi, DLCS, LOGL_ERROR, "Unable to allocate SCCP Connection ID for BSSMAP-LE to SMLC\n");
 		return -ENOSPC;
@@ -421,6 +409,7 @@ static int lb_start(void)
 	enum osmo_ss7_asp_protocol used_proto = OSMO_SS7_ASP_PROT_M3UA;
 	char inst_name[32];
 	const char *smlc_name = "smlc";
+	struct bsc_sccp_inst *bsc_sccp;
 
 	/* Already set up? */
 	if (bsc_gsmnet->smlc->sccp_user)
@@ -454,6 +443,9 @@ static int lb_start(void)
 	if (!sccp)
 		return -EINVAL;
 	bsc_gsmnet->smlc->sccp = sccp;
+	bsc_sccp = bsc_sccp_inst_alloc(tall_bsc_ctx);
+	bsc_sccp->sccp = sccp;
+	osmo_sccp_set_priv(sccp, bsc_sccp);
 
 	/* If unset, use default local SCCP address */
 	if (!bsc_gsmnet->smlc->bsc_addr.presence)

src/osmo-bsc/osmo_bsc_sigtran.c

@@ -45,26 +45,6 @@ static struct llist_head *msc_list;
 #define DEFAULT_ASP_LOCAL_IP "localhost"
 #define DEFAULT_ASP_REMOTE_IP "localhost"
 
-/* Helper function to Check if the given connection id is already assigned */
-static struct gsm_subscriber_connection *get_bsc_conn_by_conn_id(const struct osmo_sccp_user *scu, uint32_t conn_id)
-{
-	struct gsm_subscriber_connection *conn;
-	const struct osmo_sccp_instance *sccp = osmo_sccp_get_sccp(scu);
-
-	/* Range (0..SCCP_CONN_ID_MAX) expected, see bsc_sccp_inst_next_conn_id() */
-	OSMO_ASSERT(conn_id <= SCCP_CONN_ID_MAX);
-
-	llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
-		if (conn->sccp.msc && conn->sccp.msc->a.sccp != sccp)
-			continue;
-		if (conn->sccp.conn_id != conn_id)
-			continue;
-		return conn;
-	}
-
-	return NULL;
-}
-
 struct gsm_subscriber_connection *bsc_conn_by_bsub(const struct bsc_subscr *bsub)
 {
 	struct gsm_subscriber_connection *conn;
@@ -170,10 +150,12 @@ static int handle_unitdata_from_msc(const struct osmo_sccp_addr *msc_addr, struc
 static int handle_n_connect_from_msc(struct osmo_sccp_user *scu, struct osmo_scu_prim *scu_prim)
 {
 	struct bsc_msc_data *msc = get_msc_by_addr(&scu_prim->u.connect.calling_addr);
+	struct osmo_sccp_instance *sccp = osmo_sccp_get_sccp(scu);
+	struct bsc_sccp_inst *bsc_sccp = osmo_sccp_get_priv(sccp);
 	struct gsm_subscriber_connection *conn;
 	int rc = 0;
 
-	conn = get_bsc_conn_by_conn_id(scu, scu_prim->u.connect.conn_id);
+	conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.connect.conn_id);
 	if (conn) {
 		LOGP(DMSC, LOGL_NOTICE,
 		     "(calling_addr=%s conn_id=%u) N-CONNECT.ind with already used conn_id, ignoring\n",
@@ -202,6 +184,13 @@ static int handle_n_connect_from_msc(struct osmo_sccp_user *scu, struct osmo_scu
 		return -ENOMEM;
 	conn->sccp.msc = msc;
 	conn->sccp.conn_id = scu_prim->u.connect.conn_id;
+	if (bsc_sccp_inst_register_gscon(bsc_sccp, conn) < 0) {
+		LOGP(DMSC, LOGL_NOTICE, "(calling_addr=%s conn_id=%u) N-CONNECT.ind failed registering conn\n",
+		     osmo_sccp_addr_dump(&scu_prim->u.connect.calling_addr), scu_prim->u.connect.conn_id);
+		osmo_fsm_inst_term(conn->fi, OSMO_FSM_TERM_REQUEST, NULL);
+		rc = -ENOENT;
+		goto refuse;
+	}
 
 	/* Take actions asked for by the enclosed PDU */
 	osmo_fsm_inst_dispatch(conn->fi, GSCON_EV_A_CONN_IND, scu_prim);
@@ -217,6 +206,8 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 {
 	struct osmo_scu_prim *scu_prim = (struct osmo_scu_prim *)oph;
 	struct osmo_sccp_user *scu = _scu;
+	struct osmo_sccp_instance *sccp = osmo_sccp_get_sccp(scu);
+	struct bsc_sccp_inst *bsc_sccp = osmo_sccp_get_priv(sccp);
 	struct gsm_subscriber_connection *conn;
 	int rc = 0;
 
@@ -237,7 +228,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		/* Handle outbound connection confirmation */
 		DEBUGP(DMSC, "N-CONNECT.cnf(%u, %s)\n", scu_prim->u.connect.conn_id,
 		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
-		conn = get_bsc_conn_by_conn_id(scu, scu_prim->u.connect.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.connect.conn_id);
 		if (conn) {
 			osmo_fsm_inst_dispatch(conn->fi, GSCON_EV_A_CONN_CFM, scu_prim);
 			conn->sccp.state = SUBSCR_SCCP_ST_CONNECTED;
@@ -256,7 +247,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)));
 
 		/* Incoming data is a sign of a vital connection */
-		conn = get_bsc_conn_by_conn_id(scu, scu_prim->u.data.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.data.conn_id);
 		if (conn) {
 			a_reset_conn_success(conn->sccp.msc);
 			handle_data_from_msc(conn, oph->msg);
@@ -268,7 +259,7 @@ static int sccp_sap_up(struct osmo_prim_hdr *oph, void *_scu)
 		       osmo_hexdump(msgb_l2(oph->msg), msgb_l2len(oph->msg)),
 		       scu_prim->u.disconnect.cause);
 		/* indication of disconnect */
-		conn = get_bsc_conn_by_conn_id(scu, scu_prim->u.disconnect.conn_id);
+		conn = bsc_sccp_inst_get_gscon_by_conn_id(bsc_sccp, scu_prim->u.disconnect.conn_id);
 		if (conn) {
 			conn->sccp.state = SUBSCR_SCCP_ST_NONE;
 			if (msgb_l2len(oph->msg) > 0)
@@ -323,6 +314,7 @@ __attribute__((weak)) int osmo_bsc_sigtran_open_conn(struct gsm_subscriber_conne
 {
 	struct osmo_ss7_instance *ss7;
 	struct bsc_msc_data *msc;
+	struct bsc_sccp_inst *bsc_sccp;
 	uint32_t conn_id;
 	int rc;
 
@@ -338,11 +330,16 @@ __attribute__((weak)) int osmo_bsc_sigtran_open_conn(struct gsm_subscriber_conne
 		return -EINVAL;
 	}
 
-	conn->sccp.conn_id = conn_id = bsc_sccp_inst_next_conn_id(conn->sccp.msc->a.sccp);
+	bsc_sccp = osmo_sccp_get_priv(msc->a.sccp);
+	conn->sccp.conn_id = conn_id = bsc_sccp_inst_next_conn_id(bsc_sccp);
 	if (conn->sccp.conn_id == SCCP_CONN_ID_UNSET) {
 		LOGP(DMSC, LOGL_ERROR, "Unable to allocate SCCP Connection ID\n");
 		return -1;
 	}
+	if (bsc_sccp_inst_register_gscon(bsc_sccp, conn) < 0) {
+		LOGP(DMSC, LOGL_ERROR, "Unable to register SCCP connection (id=%u)\n", conn->sccp.conn_id);
+		return -1;
+	}
 	LOGP(DMSC, LOGL_DEBUG, "Allocated new connection id: %u\n", conn->sccp.conn_id);
 	ss7 = osmo_ss7_instance_find(msc->a.cs7_instance);
 	OSMO_ASSERT(ss7);
@@ -520,6 +517,7 @@ int osmo_bsc_sigtran_init(struct llist_head *mscs)
 		int prev_msc_nr;
 
 		struct osmo_sccp_instance *sccp;
+		struct bsc_sccp_inst *bsc_sccp;
 
 		llist_for_each_entry(msc, msc_list, entry) {
 			/* An MSC with invalid cs7 instance id defaults to cs7 instance 0 */
@@ -563,6 +561,10 @@ int osmo_bsc_sigtran_init(struct llist_head *mscs)
 		if (!sccp)
 			return -EINVAL;
 
+		bsc_sccp = bsc_sccp_inst_alloc(tall_bsc_ctx);
+		bsc_sccp->sccp = sccp;
+		osmo_sccp_set_priv(sccp, bsc_sccp);
+
 		/* Now that the SCCP client is set up, configure all MSCs on this cs7 instance to use it */
 		llist_for_each_entry(msc, msc_list, entry) {
 			char msc_name[32];