Index: FreeBSD/sys/cam/scsi/scsi_da.c
===================================================================
--- FreeBSD/sys/cam/scsi/scsi_da.c
+++ FreeBSD/sys/cam/scsi/scsi_da.c
@@ -309,7 +309,7 @@
 	struct   cam_iosched_softc *cam_iosched;
 	struct	 bio_queue_head delete_run_queue;
 	LIST_HEAD(, ccb_hdr) pending_ccbs;
-	int	 refcount;		/* Active xpt_action() calls */
+	int	 refcount;		/* Active CCBs */
 	da_state state;
 	da_flags flags;	
 	da_quirks quirks;
@@ -3243,7 +3243,6 @@
 		cam_periph_unlock(periph);
 		xpt_action(start_ccb);
 		cam_periph_lock(periph);
-		softc->refcount--;
 
 		/* May have more work to do, so ensure we stay scheduled */
 		daschedule(periph);
@@ -4402,6 +4401,13 @@
 		 */
 		cam_iosched_bio_complete(softc->cam_iosched, bp, done_ccb);
 		xpt_release_ccb(done_ccb);
+
+		/*
+		 * Release the periph refcount taken in dastart() for each CCB.
+		 */
+		KASSERT(softc->refcount >= 1, ("dadone softc %p refcount %d", softc, softc->refcount));
+		softc->refcount--;
+
 		if (state == DA_CCB_DELETE) {
 			TAILQ_HEAD(, bio) queue;