diff -ruNp cam.prev/cam_periph.c cam/cam_periph.c
--- cam.prev/cam_periph.c	2010-03-21 08:04:50.000000000 +0200
+++ cam/cam_periph.c	2010-03-21 08:24:08.000000000 +0200
@@ -208,7 +208,6 @@ cam_periph_alloc(periph_ctor_t *periph_c
 	periph->periph_oninval = periph_oninvalidate;
 	periph->type = type;
 	periph->periph_name = name;
-	periph->unit_number = camperiphunit(*p_drv, path_id, target_id, lun_id);
 	periph->immediate_priority = CAM_PRIORITY_NONE;
 	periph->refcount = 0;
 	periph->sim = sim;
@@ -216,31 +215,31 @@ cam_periph_alloc(periph_ctor_t *periph_c
 	status = xpt_create_path(&path, periph, path_id, target_id, lun_id);
 	if (status != CAM_REQ_CMP)
 		goto failure;
-
 	periph->path = path;
-	init_level++;
-
-	status = xpt_add_periph(periph);
-
-	if (status != CAM_REQ_CMP)
-		goto failure;
 
+	xpt_lock_buses();
+	periph->unit_number = camperiphunit(*p_drv, path_id, target_id, lun_id);
 	cur_periph = TAILQ_FIRST(&(*p_drv)->units);
 	while (cur_periph != NULL
 	    && cur_periph->unit_number < periph->unit_number)
 		cur_periph = TAILQ_NEXT(cur_periph, unit_links);
-
 	if (cur_periph != NULL)
 		TAILQ_INSERT_BEFORE(cur_periph, periph, unit_links);
 	else {
 		TAILQ_INSERT_TAIL(&(*p_drv)->units, periph, unit_links);
 		(*p_drv)->generation++;
 	}
+	xpt_unlock_buses();
 
 	init_level++;
 
-	status = periph_ctor(periph, arg);
+	status = xpt_add_periph(periph);
+	if (status != CAM_REQ_CMP)
+		goto failure;
 
+	init_level++;
+
+	status = periph_ctor(periph, arg);
 	if (status == CAM_REQ_CMP)
 		init_level++;
 
@@ -250,10 +249,12 @@ failure:
 		/* Initialized successfully */
 		break;
 	case 3:
-		TAILQ_REMOVE(&(*p_drv)->units, periph, unit_links);
 		xpt_remove_periph(periph);
 		/* FALLTHROUGH */
 	case 2:
+		xpt_lock_buses();
+		TAILQ_REMOVE(&(*p_drv)->units, periph, unit_links);
+		xpt_unlock_buses();
 		xpt_free_path(periph->path);
 		/* FALLTHROUGH */
 	case 1:
diff -ruNp cam.prev/cam_xpt.c cam/cam_xpt.c
--- cam.prev/cam_xpt.c	2010-03-21 08:04:50.000000000 +0200
+++ cam/cam_xpt.c	2010-03-21 08:07:23.000000000 +0200
@@ -2142,6 +2142,7 @@ xptpdperiphtraverse(struct periph_driver
 
 	retval = 1;
 
+	xpt_lock_buses();
 	for (periph = (start_periph ? start_periph :
 	     TAILQ_FIRST(&(*pdrv)->units)); periph != NULL;
 	     periph = next_periph) {
@@ -2149,9 +2150,12 @@ xptpdperiphtraverse(struct periph_driver
 		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);
 }