Index: if_tun.c
===================================================================
RCS file: /cvs/src/sys/net/if_tun.c,v
retrieving revision 1.230
diff -u -p -r1.230 if_tun.c
--- if_tun.c	20 Feb 2021 04:39:16 -0000	1.230
+++ if_tun.c	25 Feb 2021 07:30:38 -0000
@@ -118,7 +118,6 @@ int	tun_ioctl(struct ifnet *, u_long, ca
 void	tun_input(struct ifnet *, struct mbuf *);
 int	tun_output(struct ifnet *, struct mbuf *, struct sockaddr *,
 	    struct rtentry *);
-int	tun_enqueue(struct ifnet *, struct mbuf *);
 int	tun_clone_create(struct if_clone *, int);
 int	tap_clone_create(struct if_clone *, int);
 int	tun_create(struct if_clone *, int, int);
@@ -231,10 +230,10 @@ tun_create(struct if_clone *ifc, int uni
 	/* build the interface */
 
 	ifp->if_ioctl = tun_ioctl;
-	ifp->if_enqueue = tun_enqueue;
 	ifp->if_start = tun_start;
 	ifp->if_hardmtu = TUNMRU;
 	ifp->if_link_state = LINK_STATE_DOWN;
+	ifq_set_maxlen(&ifp->if_snd, 2048); /* XXX */
 
 	if_counters_alloc(ifp);
 
@@ -606,21 +605,6 @@ tun_output(struct ifnet *ifp, struct mbu
 	return (if_enqueue(ifp, m0));
 }
 
-int
-tun_enqueue(struct ifnet *ifp, struct mbuf *m0)
-{
-	struct tun_softc	*sc = ifp->if_softc;
-	int			 error;
-
-	error = ifq_enqueue(&ifp->if_snd, m0);
-	if (error != 0)
-		return (error);
-
-	tun_wakeup(sc);
-
-	return (0);
-}
-
 void
 tun_wakeup(struct tun_softc *sc)
 {
@@ -782,6 +766,8 @@ tun_dev_read(dev_t dev, struct uio *uio,
 	if (error != 0)
 		goto put;
 
+	KERNEL_UNLOCK();
+
 #if NBPFILTER > 0
 	if (ifp->if_bpf)
 		bpf_mtap(ifp->if_bpf, m0, BPF_DIRECTION_OUT);
@@ -803,6 +789,8 @@ tun_dev_read(dev_t dev, struct uio *uio,
 
 	m_freem(m0);
 
+	KERNEL_LOCK();
+
 put:
 	tun_put(sc);
 	return (error);
@@ -814,13 +802,21 @@ put:
 int
 tunwrite(dev_t dev, struct uio *uio, int ioflag)
 {
-	return (tun_dev_write(dev, uio, ioflag, 0));
+	int rv;
+	KERNEL_UNLOCK();
+	rv = tun_dev_write(dev, uio, ioflag, 0);
+	KERNEL_LOCK();
+	return (rv);
 }
 
 int
 tapwrite(dev_t dev, struct uio *uio, int ioflag)
 {
-	return (tun_dev_write(dev, uio, ioflag, ETHER_ALIGN));
+	int rv;
+	KERNEL_UNLOCK();
+	rv = tun_dev_write(dev, uio, ioflag, ETHER_ALIGN);
+	KERNEL_LOCK();
+	return (rv);
 }
 
 int
@@ -1060,8 +1056,7 @@ tun_start(struct ifnet *ifp)
 
 	splassert(IPL_NET);
 
-	if (ifq_len(&ifp->if_snd))
-		tun_wakeup(sc);
+	tun_wakeup(sc);
 }
 
 void
Index: ifq.c
===================================================================
RCS file: /cvs/src/sys/net/ifq.c,v
retrieving revision 1.43
diff -u -p -r1.43 ifq.c
--- ifq.c	20 Feb 2021 04:37:26 -0000	1.43
+++ ifq.c	25 Feb 2021 07:30:38 -0000
@@ -500,6 +500,9 @@ ifq_hdatalen(struct ifqueue *ifq)
 	struct mbuf *m;
 	int len = 0;
 
+	if (ifq_empty(ifq))
+		return (0);
+
 	m = ifq_deq_begin(ifq);
 	if (m != NULL) {
 		len = m->m_pkthdr.len;