[DECNET]: fix SIGPIPE

Currently recvmsg generates SIGPIPE whereas sendmsg does not; for the
other stacks it seems to be the other way round!

It also fixes the bug where reading from a socket whose peer has shutdown
returned -EINVAL rather than 0.
Signed-off-by: Patrick Caulfield <patrick@tykepenguin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/decnet/af_decnet.c

@@ -1664,17 +1664,15 @@ static int dn_recvmsg(struct kiocb *iocb, struct socket *sock,
 		goto out;
 	}
 
-	rv = dn_check_state(sk, NULL, 0, &timeo, flags);
-	if (rv)
-		goto out;
-
 	if (sk->sk_shutdown & RCV_SHUTDOWN) {
-		if (!(flags & MSG_NOSIGNAL))
-			send_sig(SIGPIPE, current, 0);
-		rv = -EPIPE;
+		rv = 0;
 		goto out;
 	}
 
+	rv = dn_check_state(sk, NULL, 0, &timeo, flags);
+	if (rv)
+		goto out;
+
 	if (flags & ~(MSG_PEEK|MSG_OOB|MSG_WAITALL|MSG_DONTWAIT|MSG_NOSIGNAL)) {
 		rv = -EOPNOTSUPP;
 		goto out;
@@ -1928,6 +1926,8 @@ static int dn_sendmsg(struct kiocb *iocb, struct socket *sock,
 
 	if (sk->sk_shutdown & SEND_SHUTDOWN) {
 		err = -EPIPE;
+		if (!(flags & MSG_NOSIGNAL))
+			send_sig(SIGPIPE, current, 0);
 		goto out_err;
 	}