rxrpc: Fix sendmsg() returning EPIPE due to recvmsg() returning ENODATA

rxrpc_sendmsg() returns EPIPE if there's an outstanding error, such as if
rxrpc_recvmsg() indicating ENODATA if there's nothing for it to read.

Change rxrpc_recvmsg() to return EAGAIN instead if there's nothing to read
as this particular error doesn't get stored in ->sk_err by the networking
core.

Also change rxrpc_sendmsg() so that it doesn't fail with delayed receive
errors (there's no way for it to report which call, if any, the error was
caused by).

Fixes: 17926a79 ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rxrpc/recvmsg.c

@@ -543,7 +543,7 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	    list_empty(&rx->recvmsg_q) &&
 	    rx->sk.sk_state != RXRPC_SERVER_LISTENING) {
 		release_sock(&rx->sk);
-		return -ENODATA;
+		return -EAGAIN;
 	}
 
 	if (list_empty(&rx->recvmsg_q)) {

net/rxrpc/sendmsg.c

@@ -304,7 +304,7 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 	/* this should be in poll */
 	sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 
-	if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))
+	if (sk->sk_shutdown & SEND_SHUTDOWN)
 		return -EPIPE;
 
 	more = msg->msg_flags & MSG_MORE;