sctp: fix missing send up SCTP_SENDER_DRY_EVENT when subscribe it

index 6766913..99e25de 100644
@@ -2073,10 +2073,33 @@ static int sctp_setsockopt_disable_fragments(struct sock *sk,
 static int sctp_setsockopt_events(struct sock *sk, char __user *optval,
 				  unsigned int optlen)
 {
+	struct sctp_association *asoc;
+	struct sctp_ulpevent *event;
+
 	if (optlen>  sizeof(struct sctp_event_subscribe))
 		return -EINVAL;
 	if (copy_from_user(&sctp_sk(sk)->subscribe, optval, optlen))
 		return -EFAULT;
+
+	/*
+	 * At the time when a user app subscribes to SCTP_SENDER_DRY_EVENT,
+	 * if there is no data to be sent or retransmit, the stack will
+	 * immediately send up this notification.
+	 */
+	if (sctp_ulpevent_type_enabled(SCTP_SENDER_DRY_EVENT,
+				&sctp_sk(sk)->subscribe)) {
+		asoc = sctp_id2assoc(sk, 0);
+
+		if (asoc&&  sctp_outq_is_empty(&asoc->outqueue)) {
+			event = sctp_ulpevent_make_sender_dry_event(asoc,
+					GFP_ATOMIC);
+			if (!event)
+				return -ENOMEM;
+
+			sctp_ulpq_tail_event(&asoc->ulpq, event);
+		}
+	}
+
 	return 0;
 }