diff --git a/sys/cam/ata/ata_da.c b/sys/cam/ata/ata_da.c
index c700e7c5d1d4..e929e518506f 100644
--- a/sys/cam/ata/ata_da.c
+++ b/sys/cam/ata/ata_da.c
@@ -1835,7 +1835,7 @@ adaflush(void)
 	struct ada_softc *softc;
 	int error;
 
-	TAILQ_FOREACH(periph, &adadriver.units, unit_links) {
+	CAM_PERIPH_FOREACH(periph, &adadriver) {
 		union ccb ccb;
 
 		/* If we paniced with lock held - not recurse here. */
@@ -1889,7 +1889,7 @@ adaspindown(uint8_t cmd, int flags)
 	struct ada_softc *softc;
 	int error;
 
-	TAILQ_FOREACH(periph, &adadriver.units, unit_links) {
+	CAM_PERIPH_FOREACH(periph, &adadriver) {
 		union ccb ccb;
 
 		/* If we paniced with lock held - not recurse here. */
@@ -1962,7 +1962,7 @@ adaresume(void *arg)
 	if (ada_spindown_suspend == 0)
 		return;
 
-	TAILQ_FOREACH(periph, &adadriver.units, unit_links) {
+	CAM_PERIPH_FOREACH(periph, &adadriver) {
 		cam_periph_lock(periph);
 		softc = (struct ada_softc *)periph->softc;
 		/*
diff --git a/sys/cam/cam_periph.h b/sys/cam/cam_periph.h
index b51fb681b2d3..bd378ec8afd1 100644
--- a/sys/cam/cam_periph.h
+++ b/sys/cam/cam_periph.h
@@ -183,6 +183,8 @@ void		cam_periph_freeze_after_event(struct cam_periph *periph,
 					      u_int duration_ms);
 int		cam_periph_error(union ccb *ccb, cam_flags camflags,
 				 u_int32_t sense_flags, union ccb *save_ccb);
+void		xpt_lock_buses(void);
+void		xpt_unlock_buses(void);
 
 static __inline void
 cam_periph_lock(struct cam_periph *periph)
@@ -209,5 +211,42 @@ cam_periph_sleep(struct cam_periph *periph, void *chan, int priority,
 	return (msleep(chan, periph->sim->mtx, priority, wmesg, timo));
 }
 
+static inline struct cam_periph *
+cam_periph_acquire_first(struct periph_driver *driver)
+{
+	struct cam_periph *periph;
+
+	xpt_lock_buses();
+	periph = TAILQ_FIRST(&driver->units);
+	while (periph != NULL && (periph->flags & CAM_PERIPH_INVALID) != 0)
+		periph = TAILQ_NEXT(periph, unit_links);
+	if (periph != NULL)
+		periph->refcount++;
+	xpt_unlock_buses();
+	return (periph);
+}
+
+static inline struct cam_periph *
+cam_periph_acquire_next(struct cam_periph *pperiph)
+{
+	struct cam_periph *periph = pperiph;
+
+	mtx_assert(pperiph->sim->mtx, MA_NOTOWNED);
+	xpt_lock_buses();
+	do {
+		periph = TAILQ_NEXT(periph, unit_links);
+	} while (periph != NULL && (periph->flags & CAM_PERIPH_INVALID) != 0);
+	if (periph != NULL)
+		periph->refcount++;
+	xpt_unlock_buses();
+	cam_periph_release(pperiph);
+	return (periph);
+}
+
+#define CAM_PERIPH_FOREACH(periph, driver)				\
+	for ((periph) = cam_periph_acquire_first(driver);		\
+	    (periph) != NULL;						\
+	    (periph) = cam_periph_acquire_next(periph))
+
 #endif /* _KERNEL */
 #endif /* _CAM_CAM_PERIPH_H */
diff --git a/sys/cam/scsi/scsi_da.c b/sys/cam/scsi/scsi_da.c
index 9fd7039b8781..aaa2a4c42e25 100644
--- a/sys/cam/scsi/scsi_da.c
+++ b/sys/cam/scsi/scsi_da.c
@@ -2848,7 +2848,7 @@ dashutdown(void * arg, int howto)
 	struct da_softc *softc;
 	int error;
 
-	TAILQ_FOREACH(periph, &dadriver.units, unit_links) {
+	CAM_PERIPH_FOREACH(periph, &dadriver) {
 		union ccb ccb;
 
 		cam_periph_lock(periph);