Index: sys/dev/usb/ucom.c
===================================================================
RCS file: /cvsroot/src/sys/dev/usb/ucom.c,v
retrieving revision 1.112
diff -n -u -r1.112 ucom.c
--- sys/dev/usb/ucom.c	10 May 2016 10:40:33 -0000	1.112
+++ sys/dev/usb/ucom.c	14 May 2016 10:22:03 -0000
@@ -174,6 +174,7 @@
 	int			sc_swflags;
 
 	u_char			sc_opening;	/* lock during open */
+	u_char			sc_closing;	/* lock during close */
 	int			sc_refcnt;
 	u_char			sc_dying;	/* disconnecting */
 
@@ -282,6 +283,7 @@
 	sc->sc_tx_stopped = 0;
 	sc->sc_swflags = 0;
 	sc->sc_opening = 0;
+	sc->sc_closing = 0;
 	sc->sc_refcnt = 0;
 	sc->sc_dying = 0;
 
@@ -542,9 +544,10 @@
 	}
 
 	/*
-	 * Do the following iff this is a first open.
+	 * Wait while the device is initialized by the
+	 * first opener or cleaned up by the last closer.
 	 */
-	while (sc->sc_opening) {
+	while (sc->sc_opening || sc->sc_closing) {
 		error = cv_wait_sig(&sc->sc_opencv, &sc->sc_lock);
 
 		if (error) {
@@ -681,6 +684,8 @@
 	mutex_enter(&sc->sc_lock);
 	tp = sc->sc_tty;
 
+	sc->sc_closing = 1;
+
 	if (!ISSET(tp->t_state, TS_ISOPEN)) {
 		goto out;
 	}
@@ -706,6 +711,9 @@
 		usb_detach_broadcast(sc->sc_dev, &sc->sc_detachcv);
 
 out:
+	sc->sc_closing = 0;
+	cv_signal(&sc->sc_opencv);
+
 	mutex_exit(&sc->sc_lock);
 
 	return 0;