commit 387fbcbf894feaa52c7040808cfea8658d131275
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Wed Dec 20 15:16:10 2017 +0900

    Ensure bridge_rtage_work to stop in bridge_stop

diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index eb237925f04..8c7c0f16b61 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -1358,7 +1358,9 @@ bridge_stop(struct ifnet *ifp, int disable)
 	KASSERT((ifp->if_flags & IFF_RUNNING) != 0);
 	ifp->if_flags &= ~IFF_RUNNING;
 
-	callout_stop(&sc->sc_brcallout);
+	callout_halt(&sc->sc_brcallout, NULL);
+	workqueue_drain(sc->sc_rtage_wq);
+
 	bstp_stop(sc);
 	bridge_rtflush(sc, IFBF_FLUSHDYN);
 }