[PATCH] eliminate hangs during RPC client shutdown

this eliminates an infinite loop in rpciod if an RPC client's reference
counter accidentally goes negative.  i've been running this under load
since 2.5.30 with no ill effects.

net/sunrpc/clnt.c

@@ -138,19 +138,27 @@ rpc_create_client(struct rpc_xprt *xprt, char *servname,
 int
 rpc_shutdown_client(struct rpc_clnt *clnt)
 {
-	dprintk("RPC: shutting down %s client for %s\n",
-		clnt->cl_protname, clnt->cl_server);
-	while (atomic_read(&clnt->cl_users)) {
-#ifdef RPC_DEBUG
-		dprintk("RPC: rpc_shutdown_client: client %s, tasks=%d\n",
-			clnt->cl_protname, atomic_read(&clnt->cl_users));
-#endif
+	dprintk("RPC: shutting down %s client for %s, tasks=%d\n",
+			clnt->cl_protname, clnt->cl_server,
+			atomic_read(&clnt->cl_users));
+
+	while (atomic_read(&clnt->cl_users) > 0) {
 		/* Don't let rpc_release_client destroy us */
 		clnt->cl_oneshot = 0;
 		clnt->cl_dead = 0;
 		rpc_killall_tasks(clnt);
 		sleep_on_timeout(&destroy_wait, 1*HZ);
 	}
+
+	if (atomic_read(&clnt->cl_users) < 0) {
+		printk(KERN_ERR "RPC: rpc_shutdown_client clnt %p tasks=%d\n",
+				clnt, atomic_read(&clnt->cl_users));
+#ifdef RPC_DEBUG
+		rpc_show_tasks();
+#endif
+		BUG();
+	}
+
 	return rpc_destroy_client(clnt);
 }