diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -572,6 +572,8 @@
 {
 	devclass_t dc;
 
+	bus_topo_assert();
+
 	PDEBUG(("looking for %s", classname));
 	if (!classname)
 		return (NULL);
@@ -712,6 +714,8 @@
 	devclass_t child_dc;
 	const char *parentname;
 
+	bus_topo_assert();
+
 	PDEBUG(("%s", DRIVERNAME(driver)));
 
 	/* Don't allow invalid pass values. */
@@ -784,6 +788,8 @@
 	device_t dev;
 	int error, i;
 
+	bus_topo_assert();
+
 	/*
 	 * Disassociate from any devices.  We iterate through all the
 	 * devices in the devclass of the driver and detach any which are
@@ -856,6 +862,8 @@
 	driverlink_t dl;
 	int error;
 
+	bus_topo_assert();
+
 	PDEBUG(("%s from devclass %s", driver->name, DEVCLANAME(busclass)));
 
 	if (!dc)
@@ -913,6 +921,8 @@
 	int i;
 	int error;
 
+	bus_topo_assert();
+
 	PDEBUG(("%s from devclass %s", driver->name, DEVCLANAME(busclass)));
 
 	if (!dc)
@@ -964,6 +974,8 @@
 {
 	driverlink_t dl;
 
+	bus_topo_assert();
+
 	PDEBUG(("%s in devclass %s", classname, DEVCLANAME(dc)));
 
 	TAILQ_FOREACH(dl, &dc->drivers, link) {
@@ -5255,6 +5267,8 @@
 	kobj_class_t driver;
 	int error, pass;
 
+	bus_topo_lock();
+
 	dmd = (struct driver_module_data *)arg;
 	bus_devclass = devclass_find_internal(dmd->dmd_busname, NULL, TRUE);
 	error = 0;
@@ -5297,6 +5311,8 @@
 		break;
 	}
 
+	bus_topo_unlock();
+
 	return (error);
 }