net: tcp: Allow immediate connection tear down

If the network interface goes down, then we do not have any time to tear down TCP connection gracefully because there is no more a connection to send data to. In this case the TCP connection is forcefully closed without going into FIN_WAIT_1 state. Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>

Author: jukkar

subsys/net/ip/net_context.c

@@ -650,7 +650,7 @@ int net_context_get(sa_family_t family, enum net_sock_type type, uint16_t proto,
  !net_if_is_ip_offloaded(net_if_get_default()) &&
  proto == IPPROTO_TCP) {
 /* Free the TCP context that we allocated earlier */
-net_tcp_put(&contexts[i]);
+net_tcp_put(&contexts[i], false);
 }
 
 return ret;
@@ -735,7 +735,7 @@ int net_context_put(struct net_context *context)
 context->send_cb = NULL;
 
 /* net_tcp_put() will handle decrementing refcount on stack's behalf */
-net_tcp_put(context);
+net_tcp_put(context, false);
 
 /* Decrement refcount on user app's behalf */
 net_context_unref(context);
@@ -777,7 +777,7 @@ int net_context_put_all(struct net_if *iface)
 contexts[i].send_cb = NULL;
 
 /* net_tcp_put() will handle decrementing refcount on stack's behalf */
-net_tcp_put(&contexts[i]);
+net_tcp_put(&contexts[i], true);
 
 /* Decrement refcount on user app's behalf */
 net_context_unref(&contexts[i]);

subsys/net/ip/tcp.c

@@ -3137,7 +3137,7 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
  * the TCP context and put the connection into
  * active close (TCP_FIN_WAIT_1).
  */
-net_tcp_put(conn->context);
+net_tcp_put(conn->context, false);
 break;
 }
 
@@ -3690,7 +3690,7 @@ static enum net_verdict tcp_in(struct tcp *conn, struct net_pkt *pkt)
 }
 
 /* Active connection close: send FIN and go to FIN_WAIT_1 state */
-int net_tcp_put(struct net_context *context)
+int net_tcp_put(struct net_context *context, bool force_close)
 {
 struct tcp *conn = context->tcp;
 
@@ -3715,24 +3715,41 @@ int net_tcp_put(struct net_context *context)
 
 /* How long to wait until all the data has been sent?
  */
-k_work_reschedule_for_queue(&tcp_work_q,
- &conn->send_data_timer,
- K_MSEC(TCP_RTO_MS));
+if (!force_close) {
+k_work_reschedule_for_queue(&tcp_work_q,
+ &conn->send_data_timer,
+ K_MSEC(TCP_RTO_MS));
+} else {
+k_work_cancel_delayable(&conn->send_data_timer);
+
+keep_alive_timer_stop(conn);
+tcp_conn_close(conn, -ENETRESET);
+}
+
 } else {
-NET_DBG("[%p] TCP connection in %s close, "
-"not disposing yet (waiting %dms)",
-conn, "active", tcp_max_timeout_ms);
-k_work_reschedule_for_queue(&tcp_work_q,
- &conn->fin_timer,
- FIN_TIMEOUT);
+if (!force_close) {
+NET_DBG("[%p] TCP connection in %s close, "
+"not disposing yet (waiting %dms)",
+conn, "active", tcp_max_timeout_ms);
+k_work_reschedule_for_queue(&tcp_work_q,
+ &conn->fin_timer,
+ FIN_TIMEOUT);
 
-tcp_out(conn, FIN | ACK);
-conn_seq(conn, + 1);
-tcp_setup_retransmission(conn);
+tcp_out(conn, FIN | ACK);
+conn_seq(conn, + 1);
+tcp_setup_retransmission(conn);
 
-conn_state(conn, TCP_FIN_WAIT_1);
+conn_state(conn, TCP_FIN_WAIT_1);
 
-keep_alive_timer_stop(conn);
+keep_alive_timer_stop(conn);
+} else {
+NET_DBG("[%p] TCP connection in %s close, "
+"disposing immediately",
+conn, "active");
+
+keep_alive_timer_stop(conn);
+tcp_conn_close(conn, -ENETRESET);
+}
 }
 } else if (conn->in_connect) {
 conn->in_connect = false;
@@ -4411,7 +4428,7 @@ enum net_verdict tp_input(struct net_conn *net_conn,
 if (is("CLOSE2", tp->op)) {
 struct tcp *conn =
 (void *)sys_slist_peek_head(&tcp_conns);
-net_tcp_put(conn->context);
+net_tcp_put(conn->context, false);
 }
 if (is("RECV", tp->op)) {
 #define HEXSTR_SIZE 64

subsys/net/ip/tcp_internal.h

@@ -354,15 +354,19 @@ static inline int net_tcp_update_recv_wnd(struct net_context *context,
  * @brief Close and delete the TCP connection for the net_context
  *
  * @param context Network context
+ * @param force_close If true, close the connection immediately. This is
+ * used e.g., when network interface goes down and we cannot wait for proper
+ * connection close procedure as we cannot send any packets anymore.
  *
  * @return 0 on success, < 0 on error
  */
 #if defined(CONFIG_NET_NATIVE_TCP)
-int net_tcp_put(struct net_context *context);
+int net_tcp_put(struct net_context *context, bool force_close);
 #else
-static inline int net_tcp_put(struct net_context *context)
+static inline int net_tcp_put(struct net_context *context, bool force_close)
 {
 ARG_UNUSED(context);
+ARG_UNUSED(force_close);
 
 return -EPROTONOSUPPORT;
 }