--- thr_rwlock.c.orig	2011-02-23 22:12:32.000000000 +0000
+++ thr_rwlock.c	2011-02-24 07:42:31.000000000 +0000
@@ -126,6 +126,10 @@
 		prwlock = *rwlock;
 	}
 
+	if (__predict_false(prwlock->owner == curthread)) {
+		return (EDEADLK);
+	}
+
 	if (curthread->rdlock_count) {
 		/*
 		 * To avoid having to track all the rdlocks held by
@@ -219,6 +223,10 @@
 		prwlock = *rwlock;
 	}
 
+	if (__predict_false(prwlock->owner == curthread)) {
+		return (EDEADLK);
+	}
+
 	if (curthread->rdlock_count) {
 		/*
 		 * To avoid having to track all the rdlocks held by
@@ -263,6 +271,10 @@
 		prwlock = *rwlock;
 	}
 
+	if (__predict_false(prwlock->owner == curthread)) {
+		return (EDEADLK);
+	}
+
 	ret = _thr_rwlock_trywrlock(&prwlock->lock);
 	if (ret == 0)
 		prwlock->owner = curthread;
@@ -290,6 +302,10 @@
 		prwlock = *rwlock;
 	}
 
+	if (__predict_false(prwlock->owner == curthread)) {
+		return (EDEADLK);
+	}
+
 	/*
 	 * POSIX said the validity of the abstimeout parameter need
 	 * not be checked if the lock can be immediately acquired.