Index: if_cdce.c
===================================================================
RCS file: /cvsroot/src/sys/dev/usb/if_cdce.c,v
retrieving revision 1.47
diff -p -u -r1.47 if_cdce.c
--- if_cdce.c	5 May 2019 03:17:54 -0000	1.47
+++ if_cdce.c	17 Jun 2019 10:10:46 -0000
@@ -271,6 +271,8 @@ cdce_attach(device_t parent, device_t se
 		eaddr[5] = (uint8_t)(device_unit(sc->cdce_dev));
 	}
 
+	mutex_init(&sc->cdce_start_lock, MUTEX_DEFAULT, IPL_NONE);
+
 	s = splnet();
 
 	aprint_normal_dev(self, "address %s\n", ether_sprintf(eaddr));
@@ -326,6 +328,8 @@ cdce_detach(device_t self, int flags)
 	sc->cdce_attached = 0;
 	splx(s);
 
+	mutex_destroy(&sc->cdce_start_lock);
+
 	return 0;
 }
 
@@ -338,12 +342,17 @@ cdce_start(struct ifnet *ifp)
 	if (sc->cdce_dying || (ifp->if_flags & IFF_OACTIVE))
 		return;
 
+	mutex_enter(&sc->cdce_start_lock);
+
 	IFQ_POLL(&ifp->if_snd, m_head);
-	if (m_head == NULL)
+	if (m_head == NULL) {
+		mutex_exit(&sc->cdce_start_lock);
 		return;
+	}
 
 	if (cdce_encap(sc, m_head, 0)) {
 		ifp->if_flags |= IFF_OACTIVE;
+		mutex_exit(&sc->cdce_start_lock);
 		return;
 	}
 
@@ -353,6 +362,8 @@ cdce_start(struct ifnet *ifp)
 
 	ifp->if_flags |= IFF_OACTIVE;
 
+	mutex_exit(&sc->cdce_start_lock);
+
 	ifp->if_timer = 6;
 }