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

BugLink: https://bugs.launchpad.net/bugs/1889928

[ Upstream commit 639f181f ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

net/rxrpc/ar-output.c

@@ -533,7 +533,7 @@ 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;

net/rxrpc/ar-recvmsg.c

@@ -78,7 +78,7 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 				release_sock(&rx->sk);
 				if (continue_call)
 					rxrpc_put_call(continue_call);
-				return -ENODATA;
+				return -EAGAIN;
 			}
 		}