Index: sys/net/bpf.c
===================================================================
--- sys/net/bpf.c	(revision 236540)
+++ sys/net/bpf.c	(working copy)
@@ -2542,13 +2542,23 @@ bpf_ifdetach(void *arg __unused, struct ifnet *ifp
 {
 	struct bpf_if *bp;
 
-	if ((bp = ifp->if_bpf) == NULL)
+	BPF_LOCK();
+	if ((bp = ifp->if_bpf) == NULL) {
+		BPF_UNLOCK();
 		return;
+	}
 
+	if ((bp->flags & BPFIF_FLAG_DYING) == 0) {
+		BPF_UNLOCK();
+		return;
+	}
+
 	CTR3(KTR_NET, "%s: freing BPF instance %p for interface %p",
 	    __func__, bp, ifp);
 
 	ifp->if_bpf = NULL;
+	BPF_UNLOCK();
+
 	rw_destroy(&bp->bif_lock);
 	free(bp, M_BPF);
 }