--- //depot/projects/smpng/sys/kern/kern_rwlock.c	2007/03/30 20:11:26
+++ //depot/user/jhb/lock/kern/kern_rwlock.c	2007/03/30 22:24:04
@@ -660,6 +650,15 @@
 	_rw_assert(rw, RA_RLOCKED, file, line);
 
 	/*
+	 * If we have multiple readers, just fail without doing any
+	 * atomic operations.
+	 */
+	if (RW_READERS(rw->rw_lock) > 1) {
+		success = 0;
+		goto out;
+	}
+
+	/*
 	 * Attempt to switch from one reader to a writer.  If there
 	 * are any write waiters, then we will have to lock the
 	 * turnstile first to prevent races with another writer