Index: sys/netinet/in.c
===================================================================
--- sys/netinet/in.c
+++ sys/netinet/in.c
@@ -998,6 +998,13 @@
 	in_pcbpurgeif0(&V_ulitecbinfo, ifp);
 	in_purgemaddrs(ifp);
 	IN_MULTI_UNLOCK();
+
+	/*
+	 * Make sure all multicast deletions invoking if_ioctl() are
+	 * completed before returning. Else we risk accessing a freed
+	 * ifnet structure pointer.
+	 */
+	inm_release_wait(NULL);
 }
 
 /*
Index: sys/netinet/in_mcast.c
===================================================================
--- sys/netinet/in_mcast.c
+++ sys/netinet/in_mcast.c
@@ -223,18 +223,38 @@
 }
 #endif
 
-static struct task free_task;
+/*
+ * Interface detach can happen in a taskqueue thread context, so we must use a
+ * dedicated thread to avoid deadlocks when draining inm_release tasks.
+ */
+TASKQUEUE_DEFINE_THREAD(inm_free);
+static struct task inm_free_task;
 static struct in_multi_head inm_free_list = SLIST_HEAD_INITIALIZER();
 static void inm_release_task(void *arg __unused, int pending __unused);
 
 static void
-inm_init(void)
+inm_init(void *arg __unused)
 {
-	TASK_INIT(&free_task, 0, inm_release_task, NULL);
+
+	TASK_INIT(&inm_free_task, 0, inm_release_task, NULL);
 }
 SYSINIT(inm_init, SI_SUB_TASKQ, SI_ORDER_ANY, inm_init, NULL);
 
 void
+inm_release_wait(void *arg __unused)
+{
+
+	/*
+	 * Make sure all pending multicast addresses are freed before
+	 * the VNET or network device is destroyed:
+	 */
+	taskqueue_drain(taskqueue_inm_free, &inm_free_task);
+}
+#ifdef VIMAGE
+VNET_SYSUNINIT(inm_release_wait, SI_SUB_PROTO_DOMAIN, SI_ORDER_FIRST, inm_release_wait, NULL);
+#endif
+
+void
 inm_release_list_deferred(struct in_multi_head *inmh)
 {
 
@@ -243,7 +263,7 @@
 	mtx_lock(&in_multi_free_mtx);
 	SLIST_CONCAT(&inm_free_list, inmh, in_multi, inm_nrele);
 	mtx_unlock(&in_multi_free_mtx);
-	taskqueue_enqueue(taskqueue_thread, &free_task);
+	taskqueue_enqueue(taskqueue_inm_free, &inm_free_task);
 }
 
 void
Index: sys/netinet/in_var.h
===================================================================
--- sys/netinet/in_var.h
+++ sys/netinet/in_var.h
@@ -450,6 +450,7 @@
 int	inm_record_source(struct in_multi *inm, const in_addr_t);
 void	inm_release_deferred(struct in_multi *);
 void	inm_release_list_deferred(struct in_multi_head *);
+void	inm_release_wait(void *);
 struct	in_multi *
 in_addmulti(struct in_addr *, struct ifnet *);
 int	in_joingroup(struct ifnet *, const struct in_addr *,
Index: sys/netinet6/in6_ifattach.c
===================================================================
--- sys/netinet6/in6_ifattach.c
+++ sys/netinet6/in6_ifattach.c
@@ -871,7 +871,7 @@
 	 * completed before returning. Else we risk accessing a freed
 	 * ifnet structure pointer.
 	 */
-	in6m_release_wait();
+	in6m_release_wait(NULL);
 }
 
 void
Index: sys/netinet6/in6_mcast.c
===================================================================
--- sys/netinet6/in6_mcast.c
+++ sys/netinet6/in6_mcast.c
@@ -520,8 +520,9 @@
 static void in6m_release_task(void *arg __unused, int pending __unused);
 
 static void
-in6m_init(void)
+in6m_init(void *arg __unused)
 {
+
 	TASK_INIT(&in6m_free_task, 0, in6m_release_task, NULL);
 }
 SYSINIT(in6m_init, SI_SUB_TASKQ, SI_ORDER_ANY, in6m_init, NULL);
@@ -538,10 +539,18 @@
 }
 
 void
-in6m_release_wait(void)
+in6m_release_wait(void *arg __unused)
 {
+
+	/*
+	 * Make sure all pending multicast addresses are freed before
+	 * the VNET or network device is destroyed:
+	 */
 	taskqueue_drain_all(taskqueue_in6m_free);
 }
+#ifdef VIMAGE
+VNET_SYSUNINIT(in6m_release_wait, SI_SUB_PROTO_DOMAIN, SI_ORDER_FIRST, in6m_release_wait, NULL);
+#endif
 
 void
 in6m_disconnect_locked(struct in6_multi_head *inmh, struct in6_multi *inm)
Index: sys/netinet6/in6_var.h
===================================================================
--- sys/netinet6/in6_var.h
+++ sys/netinet6/in6_var.h
@@ -870,7 +870,7 @@
 void	in6m_print(const struct in6_multi *);
 int	in6m_record_source(struct in6_multi *, const struct in6_addr *);
 void	in6m_release_list_deferred(struct in6_multi_head *);
-void	in6m_release_wait(void);
+void	in6m_release_wait(void *);
 void	ip6_freemoptions(struct ip6_moptions *);
 int	ip6_getmoptions(struct inpcb *, struct sockopt *);
 int	ip6_setmoptions(struct inpcb *, struct sockopt *);