sctp: signal sk_data_ready earlier on data chunks reception

Dave Miller pointed out that fb586f25 ("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 fb586f25 and signals
it as early as possible, similar to what we had before.

Fixes: fb586f25 ("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>

include/net/sctp/structs.h

@@ -218,7 +218,7 @@ struct sctp_sock {
 		frag_interleave:1,
 		recvrcvinfo:1,
 		recvnxtinfo:1,
-		pending_data_ready:1;
+		data_ready_signalled:1;
 
 	atomic_t pd_mode;
 	/* Receive to here while partial delivery is in effect. */

net/sctp/sm_sideeffect.c

@@ -1741,10 +1741,9 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
 	} else if (local_cork)
 		error = sctp_outq_uncork(&asoc->outqueue, gfp);
 
-	if (sp->pending_data_ready) {
-		sk->sk_data_ready(sk);
-		sp->pending_data_ready = 0;
-	}
+	if (sp->data_ready_signalled)
+		sp->data_ready_signalled = 0;
+
 	return error;
 nomem:
 	error = -ENOMEM;

net/sctp/ulpqueue.c

@@ -194,6 +194,7 @@ static int sctp_ulpq_clear_pd(struct sctp_ulpq *ulpq)
 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 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 		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 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 	 * 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 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 			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 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 			 * 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 @@ int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
 	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 @@ void sctp_ulpq_abort_pd(struct sctp_ulpq *ulpq, gfp_t gfp)
 {
 	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 @@ void sctp_ulpq_abort_pd(struct sctp_ulpq *ulpq, gfp_t gfp)
 		__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);
+	}
 }