[SCTP]: Include sk_buff overhead while updating the peer's receive window.

Currently if the sender is sending small messages, it can cause a receiver
to run out of receive buffer space even when the advertised receive window
is still open and results in packet drops and retransmissions. Including
a overhead while updating the sender's view of peer receive window will
reduce the chances of receive buffer space overshooting the receive window.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/output.c

@@ -633,7 +633,7 @@ static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
 		 * data will fit or delay in hopes of bundling a full
 		 * sized packet.
 		 */
-		if (len < asoc->pathmtu - packet->overhead) {
+		if (len < asoc->frag_point) {
 			retval = SCTP_XMIT_NAGLE_DELAY;
 			goto finish;
 		}
@@ -645,7 +645,13 @@ static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
 	/* Keep track of how many bytes are in flight to the receiver. */
 	asoc->outqueue.outstanding_bytes += datasize;
 
-	/* Update our view of the receiver's rwnd. */
+	/* Update our view of the receiver's rwnd. Include sk_buff overhead
+	 * while updating peer.rwnd so that it reduces the chances of a
+	 * receiver running out of receive buffer space even when receive
+	 * window is still open. This can happen when a sender is sending
+	 * sending small messages.
+	 */
+	datasize += sizeof(struct sk_buff);
 	if (datasize < rwnd)
 		rwnd -= datasize;
 	else

net/sctp/outqueue.c

@@ -416,7 +416,8 @@ void sctp_retransmit_mark(struct sctp_outq *q,
 			 * (Section 7.2.4)), add the data size of those
 			 * chunks to the rwnd.
 			 */
-			q->asoc->peer.rwnd += sctp_data_size(chunk);
+			q->asoc->peer.rwnd += (sctp_data_size(chunk) +
+						sizeof(struct sk_buff));
 			q->outstanding_bytes -= sctp_data_size(chunk);
 			transport->flight_size -= sctp_data_size(chunk);