af_iucv: block writing if msg limit is exceeded

When polling on an AF_IUCV socket, writing should be blocked if the
number of pending messages exceeds a defined limit.

Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/iucv/af_iucv.c

@@ -1490,7 +1490,7 @@ unsigned int iucv_sock_poll(struct file *file, struct socket *sock,
 	if (sk->sk_state == IUCV_DISCONN)
 		mask |= POLLIN;
 
-	if (sock_writeable(sk))
+	if (sock_writeable(sk) && iucv_below_msglim(sk))
 		mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
 	else
 		set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);