SUNRPC: Don't disconnect more than once if retransmitting NFSv4 requests

NFSv4 requires us to ensure that we break the TCP connection before we're
allowed to retransmit a request. However in the case where we're
retransmitting several requests that have been sent on the same
connection, we need to ensure that we don't interfere with the attempt to
reconnect and/or break the connection again once it has been established.

We therefore introduce a 'connection' cookie that is bumped every time a
connection is broken. This allows requests to track if they need to force a
disconnection.

Signed-off-by: Trond Myklebust <[e-mail]>

include/linux/sunrpc/xprt.h

···
 	unsigned long		rq_majortimeo;	/* major timeout alarm */
 	unsigned long		rq_timeout;	/* Current timeout value */
 	unsigned int		rq_retries;	/* # of retries */
+	unsigned int		rq_connect_cookie;
+						/* A cookie used to track the
+						   state of the transport
+						   connection */
 	
 	/*
 	 * Partial send handling
···
 	unsigned long		connect_timeout,
 				bind_timeout,
 				reestablish_timeout;
+	unsigned int		connect_cookie;	/* A cookie that gets bumped
+						   every time the transport
+						   is reconnected */
 
 	/*
 	 * Disconnection of idle transports
···
 void			xprt_release_rqst_cong(struct rpc_task *task);
 void			xprt_disconnect_done(struct rpc_xprt *xprt);
 void			xprt_force_disconnect(struct rpc_xprt *xprt);
+void			xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie);
 
 /*
  * Reserved bit positions in xprt->state

net/sunrpc/clnt.c

···
 	case -ETIMEDOUT:
 		task->tk_action = call_timeout;
 		if (task->tk_client->cl_discrtry)
-			xprt_force_disconnect(task->tk_xprt);
+			xprt_conditional_disconnect(task->tk_xprt,
+					req->rq_connect_cookie);
 		break;
 	case -ECONNREFUSED:
 	case -ENOTCONN:
···
 	if (task->tk_rqstp == req) {
 		req->rq_received = req->rq_rcv_buf.len = 0;
 		if (task->tk_client->cl_discrtry)
-			xprt_force_disconnect(task->tk_xprt);
+			xprt_conditional_disconnect(task->tk_xprt,
+					req->rq_connect_cookie);
 	}
 }
 

net/sunrpc/xprt.c

···
 	spin_unlock_bh(&xprt->transport_lock);
 }
 
+/**
+ * xprt_conditional_disconnect - force a transport to disconnect
+ * @xprt: transport to disconnect
+ * @cookie: 'connection cookie'
+ *
+ * This attempts to break the connection if and only if 'cookie' matches
+ * the current transport 'connection cookie'. It ensures that we don't
+ * try to break the connection more than once when we need to retransmit
+ * a batch of RPC requests.
+ *
+ */
+void xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie)
+{
+	/* Don't race with the test_bit() in xprt_clear_locked() */
+	spin_lock_bh(&xprt->transport_lock);
+	if (cookie != xprt->connect_cookie)
+		goto out;
+	if (test_bit(XPRT_CLOSING, &xprt->state) || !xprt_connected(xprt))
+		goto out;
+	set_bit(XPRT_CLOSE_WAIT, &xprt->state);
+	/* Try to schedule an autoclose RPC call */
+	if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
+		queue_work(rpciod_workqueue, &xprt->task_cleanup);
+	xprt_wake_pending_tasks(xprt, -ENOTCONN);
+out:
+	spin_unlock_bh(&xprt->transport_lock);
+}
+
 static void
 xprt_init_autodisconnect(unsigned long data)
 {
···
 	} else if (!req->rq_bytes_sent)
 		return;
 
+	req->rq_connect_cookie = xprt->connect_cookie;
 	status = xprt->ops->send_request(task);
 	if (status == 0) {
 		dprintk("RPC: %5u xmit complete\n", task->tk_pid);

net/sunrpc/xprtsock.c

···
 		break;
 	case TCP_FIN_WAIT1:
 		/* The client initiated a shutdown of the socket */
+		xprt->connect_cookie++;
 		xprt->reestablish_timeout = 0;
 		set_bit(XPRT_CLOSING, &xprt->state);
 		smp_mb__before_clear_bit();
···
 		set_bit(XPRT_CLOSING, &xprt->state);
 		xprt_force_disconnect(xprt);
 	case TCP_SYN_SENT:
+		xprt->connect_cookie++;
 	case TCP_CLOSING:
 		/*
 		 * If the server closed down the connection, make sure that