Index: sys/netgraph/ng_iface.c
===================================================================
--- sys/netgraph/ng_iface.c	(revision 342241)
+++ sys/netgraph/ng_iface.c	(working copy)
@@ -745,17 +745,28 @@
 ng_iface_shutdown(node_p node)
 {
 	const priv_p priv = NG_NODE_PRIVATE(node);
+	struct ifnet *ifp;
 
+	PRIV_WLOCK(priv);
+	KASSERT(priv->ifp != NULL,
+		("%s: node %p: priv->ifp == NULL", __func__, node));
+
+	ifp = priv->ifp;
+	priv->ifp = NULL;
+	PRIV_WUNLOCK(priv);
+
+	if (ifp == NULL)
+		return (0);
+
 	/*
 	 * The ifnet may be in a different vnet than the netgraph node, 
 	 * hence we have to change the current vnet context here.
 	 */
-	CURVNET_SET_QUIET(priv->ifp->if_vnet);
-	bpfdetach(priv->ifp);
-	if_detach(priv->ifp);
-	if_free(priv->ifp);
+	CURVNET_SET_QUIET(ifp->if_vnet);
+	bpfdetach(ifp);
+	if_detach(ifp);
+	if_free(ifp);
 	CURVNET_RESTORE();
-	priv->ifp = NULL;
 	free_unr(V_ng_iface_unit, priv->unit);
 	rm_destroy(&priv->lock);
 	free(priv, M_NETGRAPH_IFACE);