SUNRPC: Respond promptly to server TCP resets

If the server sends us an RST error while we're in the TCP_ESTABLISHED
state, then that will not result in a state change, and so the RPC client
ends up hanging forever (see
http://bugzilla.kernel.org/show_bug.cgi?id=11154)

We can intercept the reset by setting up an sk->sk_error_report callback,
which will then allow us to initiate a proper shutdown and retry...

We also make sure that if the send request receives an ECONNRESET, then we
shutdown too...

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/xprtsock.c

diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 9a288d5..0a50361 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -249,6 +249,7 @@
 	void			(*old_data_ready)(struct sock *, int);
 	void			(*old_state_change)(struct sock *);
 	void			(*old_write_space)(struct sock *);
+	void			(*old_error_report)(struct sock *);
 };
 
 /*
@@ -698,8 +699,9 @@
 	case -EAGAIN:
 		xs_nospace(task);
 		break;
-	case -ECONNREFUSED:
 	case -ECONNRESET:
+		xs_tcp_shutdown(xprt);
+	case -ECONNREFUSED:
 	case -ENOTCONN:
 	case -EPIPE:
 		status = -ENOTCONN;
@@ -742,6 +744,22 @@
 	xprt_release_xprt(xprt, task);
 }
 
+static void xs_save_old_callbacks(struct sock_xprt *transport, struct sock *sk)
+{
+	transport->old_data_ready = sk->sk_data_ready;
+	transport->old_state_change = sk->sk_state_change;
+	transport->old_write_space = sk->sk_write_space;
+	transport->old_error_report = sk->sk_error_report;
+}
+
+static void xs_restore_old_callbacks(struct sock_xprt *transport, struct sock *sk)
+{
+	sk->sk_data_ready = transport->old_data_ready;
+	sk->sk_state_change = transport->old_state_change;
+	sk->sk_write_space = transport->old_write_space;
+	sk->sk_error_report = transport->old_error_report;
+}
+
 /**
  * xs_close - close a socket
  * @xprt: transport
@@ -765,9 +783,8 @@
 	transport->sock = NULL;
 
 	sk->sk_user_data = NULL;
-	sk->sk_data_ready = transport->old_data_ready;
-	sk->sk_state_change = transport->old_state_change;
-	sk->sk_write_space = transport->old_write_space;
+
+	xs_restore_old_callbacks(transport, sk);
 	write_unlock_bh(&sk->sk_callback_lock);
 
 	sk->sk_no_check = 0;
@@ -1180,6 +1197,28 @@
 }
 
 /**
+ * xs_tcp_error_report - callback mainly for catching RST events
+ * @sk: socket
+ */
+static void xs_tcp_error_report(struct sock *sk)
+{
+	struct rpc_xprt *xprt;
+
+	read_lock(&sk->sk_callback_lock);
+	if (sk->sk_err != ECONNRESET || sk->sk_state != TCP_ESTABLISHED)
+		goto out;
+	if (!(xprt = xprt_from_sock(sk)))
+		goto out;
+	dprintk("RPC:       %s client %p...\n"
+			"RPC:       error %d\n",
+			__func__, xprt, sk->sk_err);
+
+	xprt_force_disconnect(xprt);
+out:
+	read_unlock(&sk->sk_callback_lock);
+}
+
+/**
  * xs_udp_write_space - callback invoked when socket buffer space
  *                             becomes available
  * @sk: socket whose state has changed
@@ -1454,10 +1493,9 @@
 
 		write_lock_bh(&sk->sk_callback_lock);
 
+		xs_save_old_callbacks(transport, sk);
+
 		sk->sk_user_data = xprt;
-		transport->old_data_ready = sk->sk_data_ready;
-		transport->old_state_change = sk->sk_state_change;
-		transport->old_write_space = sk->sk_write_space;
 		sk->sk_data_ready = xs_udp_data_ready;
 		sk->sk_write_space = xs_udp_write_space;
 		sk->sk_no_check = UDP_CSUM_NORCV;
@@ -1589,13 +1627,13 @@
 
 		write_lock_bh(&sk->sk_callback_lock);
 
+		xs_save_old_callbacks(transport, sk);
+
 		sk->sk_user_data = xprt;
-		transport->old_data_ready = sk->sk_data_ready;
-		transport->old_state_change = sk->sk_state_change;
-		transport->old_write_space = sk->sk_write_space;
 		sk->sk_data_ready = xs_tcp_data_ready;
 		sk->sk_state_change = xs_tcp_state_change;
 		sk->sk_write_space = xs_tcp_write_space;
+		sk->sk_error_report = xs_tcp_error_report;
 		sk->sk_allocation = GFP_ATOMIC;
 
 		/* socket options */