Fix several issues in GW class:

- Avoid triggering an assertion when the  gw thread is pending termination.
- Re-order gw::stop method to avoid a race condition when closing the TUN device while the gw thread is still running.

srsue/hdr/stack/upper/gw.h

@@ -44,6 +44,7 @@ class gw : public gw_interface_stack, public srsran::thread
 {
 public:
   gw(srslog::basic_logger& logger_);
+  ~gw();
   int  init(const gw_args_t& args_, stack_interface_gw* stack);
   void stop();
 
@@ -76,7 +77,7 @@ private:
   int32_t           tun_fd     = 0;
   struct ifreq      ifr        = {};
   int32_t           sock       = 0;
-  bool              if_up      = false;
+  std::atomic<bool> if_up      = {false};
 
   static const int NOT_ASSIGNED          = -1;
   int32_t          default_eps_bearer_id = NOT_ASSIGNED;

srsue/src/stack/upper/gw.cc

@@ -62,12 +62,22 @@ int gw::init(const gw_args_t& args_, stack_interface_gw* stack_)
   return SRSRAN_SUCCESS;
 }
 
+gw::~gw()
+{
+  if (tun_fd > 0) {
+    close(tun_fd);
+  }
+}
+
 void gw::stop()
 {
   if (run_enable) {
     run_enable = false;
     if (if_up) {
-      close(tun_fd);
+      if_up = false;
+      if (running) {
+        thread_cancel();
+      }
 
       // Wait thread to exit gracefully otherwise might leave a mutex locked
       int cnt = 0;
@@ -75,9 +85,6 @@ void gw::stop()
         usleep(10000);
         cnt++;
       }
-      if (running) {
-        thread_cancel();
-      }
       wait_thread_finish();
 
       current_ip_addr = 0;
@@ -125,7 +132,9 @@ void gw::write_pdu(uint32_t lcid, srsran::unique_byte_buffer_t pdu)
     dl_tput_bytes += pdu->N_bytes;
   }
   if (!if_up) {
+    if (run_enable) {
       logger.warning("TUN/TAP not up - dropping gw RX message");
+    }
   } else if (pdu->N_bytes < 20) {
     // Packet not large enough to hold IPv4 Header
     logger.warning("Packet to small to hold IPv4 header. Dropping packet with %d B", pdu->N_bytes);
@@ -163,7 +172,9 @@ void gw::write_pdu_mch(uint32_t lcid, srsran::unique_byte_buffer_t pdu)
     memcpy(&dst_addr.s_addr, &pdu->msg[16], 4);
 
     if (!if_up) {
+      if (run_enable) {
         logger.warning("TUN/TAP not up - dropping gw RX message");
+      }
     } else {
       int n = write(tun_fd, pdu->msg, pdu->N_bytes);
       if (n > 0 && (pdu->N_bytes != (uint32_t)n)) {
@@ -324,6 +335,10 @@ void gw::run_thread()
           continue;
         }
 
+        if (!run_enable) {
+          break;
+        }
+
         // Beyond this point we should have a activated default EPS bearer
         srsran_assert(default_eps_bearer_id != NOT_ASSIGNED, "Default EPS bearer not activated");