Index: sys/net/if.c
===================================================================
--- sys/net/if.c
+++ sys/net/if.c
@@ -1500,23 +1500,18 @@
 }
 
 /*
- * Remove a group from an interface
+ * Helper function to release group memory in if_delgroup and if_delgroups.
+ * Note this function assumes the IFNET lock is held, and will release it in
+ * order to call group event handlers.
  */
-int
-if_delgroup(struct ifnet *ifp, const char *groupname)
+static void
+if_freegroup(struct ifnet *ifp, struct ifg_list *ifgl, const char *groupname)
 {
-	struct ifg_list		*ifgl;
 	struct ifg_member	*ifgm;
 	int freeifgl;
 
-	IFNET_WLOCK();
-	CK_STAILQ_FOREACH(ifgl, &ifp->if_groups, ifgl_next)
-		if (!strcmp(ifgl->ifgl_group->ifg_group, groupname))
-			break;
-	if (ifgl == NULL) {
-		IFNET_WUNLOCK();
-		return (ENOENT);
-	}
+	/* Ensure we have the IFNET lock */
+	IFNET_WLOCK_ASSERT();
 
 	freeifgl = 0;
 	IF_ADDR_WLOCK(ifp);
@@ -1534,6 +1529,8 @@
 		CK_STAILQ_REMOVE(&V_ifg_head, ifgl->ifgl_group, ifg_group, ifg_next);
 		freeifgl = 1;
 	}
+
+	/* Drop the lock so that the event handler can be called */
 	IFNET_WUNLOCK();
 
 	epoch_wait_preempt(net_epoch_preempt);
@@ -1545,6 +1542,27 @@
 	free(ifgl, M_TEMP);
 
 	EVENTHANDLER_INVOKE(group_change_event, groupname);
+}
+
+/*
+ * Remove a group from an interface
+ */
+int
+if_delgroup(struct ifnet *ifp, const char *groupname)
+{
+	struct ifg_list		*ifgl;
+
+	IFNET_WLOCK();
+	CK_STAILQ_FOREACH(ifgl, &ifp->if_groups, ifgl_next)
+		if (!strcmp(ifgl->ifgl_group->ifg_group, groupname))
+			break;
+	if (ifgl == NULL) {
+		IFNET_WUNLOCK();
+		return (ENOENT);
+	}
+
+	/* if_freegroup will call IFNET_WUNLOCK() */
+	if_freegroup(ifp, ifgl, groupname);
 
 	return (0);
 }
@@ -1556,9 +1574,7 @@
 if_delgroups(struct ifnet *ifp)
 {
 	struct ifg_list		*ifgl;
-	struct ifg_member	*ifgm;
 	char groupname[IFNAMSIZ];
-	int ifglfree;
 
 	IFNET_WLOCK();
 	while (!CK_STAILQ_EMPTY(&ifp->if_groups)) {
@@ -1566,32 +1582,8 @@
 
 		strlcpy(groupname, ifgl->ifgl_group->ifg_group, IFNAMSIZ);
 
-		IF_ADDR_WLOCK(ifp);
-		CK_STAILQ_REMOVE(&ifp->if_groups, ifgl, ifg_list, ifgl_next);
-		IF_ADDR_WUNLOCK(ifp);
-
-		CK_STAILQ_FOREACH(ifgm, &ifgl->ifgl_group->ifg_members, ifgm_next)
-			if (ifgm->ifgm_ifp == ifp)
-				break;
-
-		if (ifgm != NULL)
-			CK_STAILQ_REMOVE(&ifgl->ifgl_group->ifg_members, ifgm, ifg_member,
-			    ifgm_next);
-		ifglfree = 0;
-		if (--ifgl->ifgl_group->ifg_refcnt == 0) {
-			CK_STAILQ_REMOVE(&V_ifg_head, ifgl->ifgl_group, ifg_group, ifg_next);
-			ifglfree = 1;
-		}
-
-		IFNET_WUNLOCK();
-		epoch_wait_preempt(net_epoch_preempt);
-		free(ifgm, M_TEMP);
-		if (ifglfree) {
-			EVENTHANDLER_INVOKE(group_detach_event,
-								ifgl->ifgl_group);
-			free(ifgl->ifgl_group, M_TEMP);
-		}
-		EVENTHANDLER_INVOKE(group_change_event, groupname);
+		/* if_freegroup calls IFNET_WUNLOCK() */
+		if_freegroup(ifp, ifgl, groupname);
 
 		IFNET_WLOCK();
 	}