SUNRPC: Ensure timely close of disconnected AF_LOCAL sockets

When the rpcbind server closes the socket, we need to ensure that the
socket is closed by the kernel as soon as feasible, so add a
sk_state_change callback to trigger this close.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/xprtsock.c

@@ -1418,6 +1418,26 @@ static size_t xs_tcp_bc_maxpayload(struct rpc_xprt *xprt)
 }
 #endif /* CONFIG_SUNRPC_BACKCHANNEL */
 
+/**
+ * xs_local_state_change - callback to handle AF_LOCAL socket state changes
+ * @sk: socket whose state has changed
+ *
+ */
+static void xs_local_state_change(struct sock *sk)
+{
+	struct rpc_xprt *xprt;
+	struct sock_xprt *transport;
+
+	if (!(xprt = xprt_from_sock(sk)))
+		return;
+	transport = container_of(xprt, struct sock_xprt, xprt);
+	if (sk->sk_shutdown & SHUTDOWN_MASK) {
+		clear_bit(XPRT_CONNECTED, &xprt->state);
+		/* Trigger the socket release */
+		xs_run_error_worker(transport, XPRT_SOCK_WAKE_DISCONNECT);
+	}
+}
+
 /**
  * xs_tcp_state_change - callback to handle TCP socket state changes
  * @sk: socket whose state has changed
@@ -1866,6 +1886,7 @@ static int xs_local_finish_connecting(struct rpc_xprt *xprt,
 		sk->sk_user_data = xprt;
 		sk->sk_data_ready = xs_data_ready;
 		sk->sk_write_space = xs_udp_write_space;
+		sk->sk_state_change = xs_local_state_change;
 		sk->sk_error_report = xs_error_report;
 
 		xprt_clear_connected(xprt);