Index: head/sys/net/if.c
===================================================================
--- head/sys/net/if.c
+++ head/sys/net/if.c
@@ -173,7 +173,7 @@
 static int	if_getgroupmembers(struct ifgroupreq *);
 static void	if_delgroups(struct ifnet *);
 static void	if_attach_internal(struct ifnet *, int, struct if_clone *);
-static void	if_detach_internal(struct ifnet *, int, struct if_clone **);
+static int	if_detach_internal(struct ifnet *, int, struct if_clone **);
 
 #ifdef INET6
 /*
@@ -884,7 +884,7 @@
 	CURVNET_RESTORE();
 }
 
-static void
+static int
 if_detach_internal(struct ifnet *ifp, int vmove, struct if_clone **ifcp)
 {
 	struct ifaddr *ifa;
@@ -906,11 +906,19 @@
 #endif
 	IFNET_WUNLOCK();
 	if (!found) {
+		/*
+		 * While we would want to panic here, we cannot
+		 * guarantee that the interface is indeed still on
+		 * the list given we don't hold locks all the way.
+		 */
+		return (ENOENT);
+#if 0
 		if (vmove)
 			panic("%s: ifp=%p not on the ifnet tailq %p",
 			    __func__, ifp, &V_ifnet);
 		else
 			return; /* XXX this should panic as well? */
+#endif
 	}
 
 	/* Check if this is a cloned interface or not. */
@@ -993,6 +1001,8 @@
 			(*dp->dom_ifdetach)(ifp,
 			    ifp->if_afdata[dp->dom_family]);
 	}
+
+	return (0);
 }
 
 #ifdef VIMAGE
@@ -1007,12 +1017,16 @@
 if_vmove(struct ifnet *ifp, struct vnet *new_vnet)
 {
 	struct if_clone *ifc;
+	int rc;
 
 	/*
 	 * Detach from current vnet, but preserve LLADDR info, do not
 	 * mark as dead etc. so that the ifnet can be reattached later.
+	 * If we cannot find it, we lost the race to someone else.
 	 */
-	if_detach_internal(ifp, 1, &ifc);
+	rc = if_detach_internal(ifp, 1, &ifc);
+	if (rc != 0)
+		return;
 
 	/*
 	 * Unlink the ifnet from ifindex_table[] in current vnet, and shrink