Index: ifq.c
===================================================================
RCS file: /cvs/src/sys/net/ifq.c,v
retrieving revision 1.7
diff -u -p -r1.7 ifq.c
--- ifq.c	7 Mar 2017 01:29:53 -0000	1.7
+++ ifq.c	7 Mar 2017 03:26:30 -0000
@@ -402,12 +402,32 @@ priq_enq(struct ifqueue *ifq, struct mbu
 {
 	struct priq *pq;
 	struct priq_list *pl;
-
-	if (ifq_len(ifq) >= ifq->ifq_maxlen)
-		return (m);
+	struct mbuf *dm = NULL;
 
 	pq = ifq->ifq_q;
 	KASSERT(m->m_pkthdr.pf.prio <= IFQ_MAXPRIO);
+
+	if (ifq_len(ifq) >= ifq->ifq_maxlen) {
+		unsigned int prio;
+
+		/* Find a lower priority queue to drop from */
+		for (prio = 0; prio < m->m_pkthdr.pf.prio; prio++) {
+			pl = &pq->pq_lists[prio];
+			if (pl->head != NULL) {
+				dm = pl->head;
+				priq_deq_commit(ifq, dm, pl);
+				goto enqueue;
+			}
+		}
+
+		/*
+		 * There's no lower priority queue that we can
+		 * drop from so don't enqueue this one.
+		 */
+		return (m);
+	}
+
+enqueue:
 	pl = &pq->pq_lists[m->m_pkthdr.pf.prio];
 
 	m->m_nextpkt = NULL;
@@ -417,7 +437,7 @@ priq_enq(struct ifqueue *ifq, struct mbu
 		pl->tail->m_nextpkt = m;
 	pl->tail = m;
 
-	return (NULL);
+	return (dm);
 }
 
 struct mbuf *