Index: ifq.c
===================================================================
RCS file: /cvs/src/sys/net/ifq.c,v
retrieving revision 1.3
diff -u -p -r1.3 ifq.c
--- ifq.c	9 Dec 2015 12:07:42 -0000	1.3
+++ ifq.c	29 Dec 2015 11:19:37 -0000
@@ -83,8 +83,8 @@ ifq_serialize(struct ifqueue *ifq, struc
 		TAILQ_INSERT_TAIL(&ifq->ifq_task_list, t, t_entry);
 	}
 
-	if (ifq->ifq_serializer == 0) {
-		ifq->ifq_serializer = 1;
+	if (ifq->ifq_serializer == NULL) {
+		ifq->ifq_serializer = curcpu();
 
 		while ((t = TAILQ_FIRST(&ifq->ifq_task_list)) != NULL) {
 			TAILQ_REMOVE(&ifq->ifq_task_list, t, t_entry);
@@ -98,11 +98,17 @@ ifq_serialize(struct ifqueue *ifq, struc
 			mtx_enter(&ifq->ifq_task_mtx);
 		}
 
-		ifq->ifq_serializer = 0;
+		ifq->ifq_serializer = NULL;
 	}
 	mtx_leave(&ifq->ifq_task_mtx);
 }
 
+int
+ifq_is_serialized(struct ifqueue *ifq)
+{
+	return (ifq->ifq_serializer == curcpu());
+}
+
 void
 ifq_start_task(void *p)
 {
@@ -136,7 +142,7 @@ ifq_barrier(struct ifqueue *ifq)
 	/* this should only be called from converted drivers */
 	KASSERT(ISSET(ifq->ifq_if->if_xflags, IFXF_MPSAFE));
 
-	if (ifq->ifq_serializer == 0)
+	if (ifq->ifq_serializer == NULL)
 		return;
 
 	ifq_serialize(ifq, &t);
@@ -176,7 +182,7 @@ ifq_init(struct ifqueue *ifq, struct ifn
 
 	mtx_init(&ifq->ifq_task_mtx, IPL_NET);
 	TAILQ_INIT(&ifq->ifq_task_list);
-	ifq->ifq_serializer = 0;
+	ifq->ifq_serializer = NULL;
 
 	task_set(&ifq->ifq_start, ifq_start_task, ifq);
 	task_set(&ifq->ifq_restart, ifq_restart_task, ifq);
Index: ifq.h
===================================================================
RCS file: /cvs/src/sys/net/ifq.h,v
retrieving revision 1.3
diff -u -p -r1.3 ifq.h
--- ifq.h	10 Dec 2015 03:05:17 -0000	1.3
+++ ifq.h	29 Dec 2015 11:19:37 -0000
@@ -37,7 +37,7 @@ struct ifqueue {
 	/* work serialisation */
 	struct mutex		 ifq_task_mtx;
 	struct task_list	 ifq_task_list;
-	unsigned int		 ifq_serializer;
+	void			*ifq_serializer;
 
 	/* work to be serialised */
 	struct task		 ifq_start;
@@ -149,8 +149,9 @@ struct ifqueue {
  * == Network Driver API
  * 
  * The API used by network drivers is mostly documented in the
- * ifq_dequeue(9) manpage except for ifq_serialize().
- * 
+ * ifq_dequeue(9) manpage except for ifq_serialize(),
+ * ifq_is_serialized(), and IFQ_ASSERT_SERIALIZED().
+ *
  * === ifq_serialize()
  * 
  * A driver may run arbitrary work in the ifqueue serialiser context
@@ -163,6 +164,16 @@ struct ifqueue {
  * Because the work may be run on another CPU, the lifetime of the
  * task and the work it represents can extend beyond the end of the
  * call to ifq_serialize() that dispatched it.
+ *
+ * === ifq_is_serialized()
+ *
+ * This function returns whether the caller is currently within the
+ * ifqueue serializer context.
+ *
+ * === IFQ_ASSERT_SERIALIZED()
+ *
+ * This macro will assert that the caller is currently within the
+ * specified ifqueue serialiser context.
  * 
  * 
  * = ifqueue work serialisation
@@ -318,6 +329,7 @@ unsigned int	 ifq_purge(struct ifqueue *
 void		*ifq_q_enter(struct ifqueue *, const struct ifq_ops *);
 void		 ifq_q_leave(struct ifqueue *, void *);
 void		 ifq_serialize(struct ifqueue *, struct task *);
+int		 ifq_is_serialized(struct ifqueue *);
 void		 ifq_barrier(struct ifqueue *);
 
 #define	ifq_len(_ifq)			((_ifq)->ifq_len)
@@ -353,6 +365,8 @@ ifq_restart(struct ifqueue *ifq)
 {
 	ifq_serialize(ifq, &ifq->ifq_restart);
 }
+
+#define IFQ_ASSERT_SERIALIZED(_ifq)	KASSERT(ifq_is_serialized(_ifq))
 
 extern const struct ifq_ops * const ifq_priq_ops;