Index: sys/cam/cam_periph.c
===================================================================
--- sys/cam/cam_periph.c	(revision 205349)
+++ sys/cam/cam_periph.c	(working copy)
@@ -204,6 +204,7 @@
 	if (status != CAM_REQ_CMP)
 		goto failure;
 
+	xpt_lock_buses();
 	cur_periph = TAILQ_FIRST(&(*p_drv)->units);
 	while (cur_periph != NULL
 	    && cur_periph->unit_number < periph->unit_number)
@@ -215,6 +216,7 @@
 		TAILQ_INSERT_TAIL(&(*p_drv)->units, periph, unit_links);
 		(*p_drv)->generation++;
 	}
+	xpt_unlock_buses();
 
 	init_level++;
 
@@ -229,7 +231,9 @@
 		/* Initialized successfully */
 		break;
 	case 3:
+		xpt_lock_buses();
 		TAILQ_REMOVE(&(*p_drv)->units, periph, unit_links);
+		xpt_unlock_buses();
 		xpt_remove_periph(periph);
 		/* FALLTHROUGH */
 	case 2:
@@ -391,11 +395,15 @@
 	periph_name = p_drv->driver_name;
 	for (;;newunit++) {
 
+		xpt_lock_buses();
 		for (periph = TAILQ_FIRST(&p_drv->units);
 		     periph != NULL && periph->unit_number != newunit;
 		     periph = TAILQ_NEXT(periph, unit_links))
 			;
 
+		/* XXX: Maybe the periph might be refcounted here? */
+		xpt_unlock_buses();
+
 		if (periph != NULL && periph->unit_number == newunit) {
 			if (wired != 0) {
 				xpt_print(periph->path, "Duplicate Wired "
Index: sys/cam/scsi/scsi_da.c
===================================================================
--- sys/cam/scsi/scsi_da.c	(revision 205349)
+++ sys/cam/scsi/scsi_da.c	(working copy)
@@ -2020,6 +2020,7 @@
 	struct cam_periph *periph;
 	struct da_softc *softc;
 
+	xpt_lock_buses();
 	TAILQ_FOREACH(periph, &dadriver.units, unit_links) {
 		union ccb ccb;
 
@@ -2078,6 +2079,7 @@
 					 /*getcount_only*/0);
 		cam_periph_unlock(periph);
 	}
+	xpt_unlock_buses();
 }
 
 #else /* !_KERNEL */
Index: sys/cam/cam_xpt.c
===================================================================
--- sys/cam/cam_xpt.c	(revision 205349)
+++ sys/cam/cam_xpt.c	(working copy)
@@ -2784,6 +2784,7 @@
 
 	retval = 1;
 
+	xpt_lock_buses();
 	for (periph = (start_periph ? start_periph :
 	     TAILQ_FIRST(&(*pdrv)->units)); periph != NULL;
 	     periph = next_periph) {
@@ -2791,9 +2792,12 @@
 		next_periph = TAILQ_NEXT(periph, unit_links);
 
 		retval = tr_func(periph, arg);
-		if (retval == 0)
+		if (retval == 0) {
+			xpt_unlock_buses();
 			return(retval);
+		}
 	}
+	xpt_unlock_buses();
 	return(retval);
 }