--- if_stf.c	Wed Mar 10 13:50:25 2004
+++ /home/rwatson/p4/rwatson_netperf/sys/net/if_stf.c	Fri Mar 12 09:09:17 2004
@@ -136,13 +136,11 @@
 #define sc_ro	__sc_ro46.__sc_ro4
 	const struct encaptab *encap_cookie;
 	LIST_ENTRY(stf_softc) sc_list;	/* all stf's are linked */
+	struct mtx	sc_mtx;		/* protect sc_ro */
 };
 
 /*
  * All mutable global variables in if_stf.c are protected by stf_mtx.
- * XXXRW: Note that mutable fields in the softc are not currently locked:
- * in particular, sc_ro needs to be protected from concurrent entrance
- * of stf_output().
  */
 static struct mtx stf_mtx;
 static LIST_HEAD(, stf_softc) stf_softc_list;
@@ -196,6 +194,7 @@
 		free(sc, M_STF);
 		return (ENOMEM);
 	}
+	mtx_init(&sc->sc_mtx, "stf sc_mtx", NULL, MTX_DEF);
 
 	sc->sc_if.if_mtu    = IPV6_MMTU;
 	sc->sc_if.if_ioctl  = stf_ioctl;
@@ -220,6 +219,7 @@
 	bpfdetach(&sc->sc_if);
 	if_detach(&sc->sc_if);
 
+	mtx_destroy(&sc->sc_mtx);
 	free(sc, M_STF);
 }
 
@@ -391,9 +391,10 @@
 	struct ip *ip;
 	struct ip6_hdr *ip6;
 	struct in6_ifaddr *ia6;
-#ifdef MAC
+	struct route ro;
 	int error;
 
+#ifdef MAC
 	error = mac_check_ifnet_transmit(ifp, m);
 	if (error) {
 		m_freem(m);
@@ -495,9 +496,7 @@
 	else
 		ip_ecn_ingress(ECN_NOCARE, &ip->ip_tos, &tos);
 
-	/*
-	 * XXXRW: Locking of sc_ro required.
-	 */
+	mtx_lock(&sc->sc_mtx);
 	dst4 = (struct sockaddr_in *)&sc->sc_ro.ro_dst;
 	if (dst4->sin_family != AF_INET ||
 	    bcmp(&dst4->sin_addr, &ip->ip_dst, sizeof(ip->ip_dst)) != 0) {
@@ -516,12 +515,21 @@
 		if (sc->sc_ro.ro_rt == NULL) {
 			m_freem(m);
 			ifp->if_oerrors++;
+			mtx_unlock(&sc->sc_mtx);
 			return ENETUNREACH;
 		}
 	}
 
+	/*
+	 * XXXRW: Holding mutex over call to ip_output(): potential lock
+	 * order issue?  Hard to resolve cleanly with the current route
+	 * caching model, as we have to synchronize access to shared softc
+	 * state.
+	 */
 	ifp->if_opackets++;
-	return ip_output(m, NULL, &sc->sc_ro, 0, NULL, NULL);
+	error = ip_output(m, NULL, &ro, 0, NULL, NULL);
+	mtx_unlock(&sc->sc_mtx);
+	return (error);
 }
 
 static int