SUNRPC: ECONNREFUSED should cause a rebind.

If you
- mount and NFSv3 filesystem
- do some file locking which requires the server
to make a GRANT call back
- unmount
- mount again and do the same locking

then the second attempt at locking suffers a 30 second delay.
Unmounting and remounting causes lockd to stop and restart,
which causes it to bind to a new port.
The server still thinks the old port is valid and gets ECONNREFUSED
when trying to contact it.
ECONNREFUSED should be seen as a hard error that is not worth
retrying. Rebinding is the only reasonable response.

This patch forces a rebind if that makes sense.

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

net/sunrpc/clnt.c

···
 	task->tk_status = 0;
 	switch (status) {
 	case -ECONNREFUSED:
+		/* A positive refusal suggests a rebind is needed. */
+		if (RPC_IS_SOFTCONN(task))
+			break;
+		if (clnt->cl_autobind) {
+			rpc_force_rebind(clnt);
+			task->tk_action = call_bind;
+			return;
+		}
 	case -ECONNRESET:
 	case -ECONNABORTED:
 	case -ENETUNREACH: