SUNRPC: Don't auto-disconnect from the local rpcbind socket

There is no need for the kernel to time out the AF_LOCAL connection to
the rpcbind socket, and doing so is problematic because when it is
time to reconnect, our process may no longer be using the same mount
namespace.
Reported-by: Nix <nix@esperi.org.uk>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Jeff Layton <jlayton@redhat.com>
Cc: stable@vger.kernel.org # 3.9.x

net/sunrpc/rpcb_clnt.c

@@ -238,6 +238,14 @@ static int rpcb_create_local_unix(struct net *net)
 		.program	= &rpcb_program,
 		.version	= RPCBVERS_2,
 		.authflavor	= RPC_AUTH_NULL,
+		/*
+		 * We turn off the idle timeout to prevent the kernel
+		 * from automatically disconnecting the socket.
+		 * Otherwise, we'd have to cache the mount namespace
+		 * of the caller and somehow pass that to the socket
+		 * reconnect code.
+		 */
+		.flags		= RPC_CLNT_CREATE_NO_IDLE_TIMEOUT,
 	};
 	struct rpc_clnt *clnt, *clnt4;
 	int result = 0;