Index: kern_rwlock.c
===================================================================
--- kern_rwlock.c	(revision 191765)
+++ kern_rwlock.c	(working copy)
@@ -202,8 +202,12 @@ _rw_try_wlock(struct rwlock *rw, const char *file,
 	KASSERT(rw->rw_lock != RW_DESTROYED,
 	    ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
 
-	if (rw_wlocked(rw) && (rw->lock_object.lo_flags & RW_RECURSE) != 0) {
+	if (rw_wlocked(rw)) {
+		KASSERT(rw->lock_object.lo_flags & RW_RECURSE,
+		    ("%s: recursing but non-recursive rw %s @ %s:%d\n",
+		    __func__, rw->lock_object.lo_name, file, line));
 		rw->rw_recurse++;
+		atomic_set_ptr(&rw->rw_lock, RW_LOCK_RECURSED);
 		rval = 1;
 	} else
 		rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED,