sctp: signal sk_data_ready earlier on data chunks reception

Dave Miller pointed out that fb586f25300f ("sctp: delay calls to
sk_data_ready() as much as possible") may insert latency specially if
the receiving application is running on another CPU and that it would be
better if we signalled as early as possible.

This patch thus basically inverts the logic on fb586f25300f and signals
it as early as possible, similar to what we had before.

Fixes: fb586f25300f ("sctp: delay calls to sk_data_ready() as much as possible")
Reported-by: Dave Miller <davem@davemloft.net>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/ulpqueue.c b/net/sctp/ulpqueue.c
index ec12a89..ec166d2 100644
--- a/net/sctp/ulpqueue.c
+++ b/net/sctp/ulpqueue.c
@@ -194,6 +194,7 @@
 int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 {
 	struct sock *sk = ulpq->asoc->base.sk;
+	struct sctp_sock *sp = sctp_sk(sk);
 	struct sk_buff_head *queue, *skb_list;
 	struct sk_buff *skb = sctp_event2skb(event);
 	int clear_pd = 0;
@@ -211,7 +212,7 @@
 		sk_incoming_cpu_update(sk);
 	}
 	/* Check if the user wishes to receive this event.  */
-	if (!sctp_ulpevent_is_enabled(event, &sctp_sk(sk)->subscribe))
+	if (!sctp_ulpevent_is_enabled(event, &sp->subscribe))
 		goto out_free;
 
 	/* If we are in partial delivery mode, post to the lobby until
@@ -219,7 +220,7 @@
 	 * the association the cause of the partial delivery.
 	 */
 
-	if (atomic_read(&sctp_sk(sk)->pd_mode) == 0) {
+	if (atomic_read(&sp->pd_mode) == 0) {
 		queue = &sk->sk_receive_queue;
 	} else {
 		if (ulpq->pd_mode) {
@@ -231,7 +232,7 @@
 			if ((event->msg_flags & MSG_NOTIFICATION) ||
 			    (SCTP_DATA_NOT_FRAG ==
 				    (event->msg_flags & SCTP_DATA_FRAG_MASK)))
-				queue = &sctp_sk(sk)->pd_lobby;
+				queue = &sp->pd_lobby;
 			else {
 				clear_pd = event->msg_flags & MSG_EOR;
 				queue = &sk->sk_receive_queue;
@@ -242,10 +243,10 @@
 			 * can queue this to the receive queue instead
 			 * of the lobby.
 			 */
-			if (sctp_sk(sk)->frag_interleave)
+			if (sp->frag_interleave)
 				queue = &sk->sk_receive_queue;
 			else
-				queue = &sctp_sk(sk)->pd_lobby;
+				queue = &sp->pd_lobby;
 		}
 	}
 
@@ -264,8 +265,10 @@
 	if (clear_pd)
 		sctp_ulpq_clear_pd(ulpq);
 
-	if (queue == &sk->sk_receive_queue)
-		sctp_sk(sk)->pending_data_ready = 1;
+	if (queue == &sk->sk_receive_queue && !sp->data_ready_signalled) {
+		sp->data_ready_signalled = 1;
+		sk->sk_data_ready(sk);
+	}
 	return 1;
 
 out_free:
@@ -1126,11 +1129,13 @@
 {
 	struct sctp_ulpevent *ev = NULL;
 	struct sock *sk;
+	struct sctp_sock *sp;
 
 	if (!ulpq->pd_mode)
 		return;
 
 	sk = ulpq->asoc->base.sk;
+	sp = sctp_sk(sk);
 	if (sctp_ulpevent_type_enabled(SCTP_PARTIAL_DELIVERY_EVENT,
 				       &sctp_sk(sk)->subscribe))
 		ev = sctp_ulpevent_make_pdapi(ulpq->asoc,
@@ -1140,6 +1145,8 @@
 		__skb_queue_tail(&sk->sk_receive_queue, sctp_event2skb(ev));
 
 	/* If there is data waiting, send it up the socket now. */
-	if (sctp_ulpq_clear_pd(ulpq) || ev)
-		sctp_sk(sk)->pending_data_ready = 1;
+	if ((sctp_ulpq_clear_pd(ulpq) || ev) && !sp->data_ready_signalled) {
+		sp->data_ready_signalled = 1;
+		sk->sk_data_ready(sk);
+	}
 }