sctp: Restore 'resent' bit to avoid retransmitted chunks for RTT measurements

Currently retransmitted DATA chunks could also be used for
RTT measurements since there are no flag to identify whether
the transmitted DATA chunk is a new one or a retransmitted one.
This problem is introduced by commit ae19c5486 ("sctp: remove
'resent' bit from the chunk") which inappropriately removed the
'resent' bit completely, instead of doing this, we should set
the resent bit only for the retransmitted DATA chunks.

Signed-off-by: Xufeng Zhang <xufeng.zhang@windriver.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sctp/structs.h

@@ -629,6 +629,7 @@ struct sctp_chunk {
 #define SCTP_NEED_FRTX 0x1
 #define SCTP_DONT_FRTX 0x2
 	__u16	rtt_in_progress:1,	/* This chunk used for RTT calc? */
+		resent:1,		/* Has this chunk ever been resent. */
 		has_tsn:1,		/* Does this chunk have a TSN yet? */
 		has_ssn:1,		/* Does this chunk have a SSN yet? */
 		singleton:1,		/* Only chunk in the packet? */

net/sctp/output.c

@@ -474,10 +474,11 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 			 * for a given destination transport address.
 			 */
 
-			if (!tp->rto_pending) {
+			if (!chunk->resent && !tp->rto_pending) {
 				chunk->rtt_in_progress = 1;
 				tp->rto_pending = 1;
 			}
+
 			has_data = 1;
 		}
 

net/sctp/outqueue.c

@@ -446,6 +446,8 @@ void sctp_retransmit_mark(struct sctp_outq *q,
 				transport->rto_pending = 0;
 			}
 
+			chunk->resent = 1;
+
 			/* Move the chunk to the retransmit queue. The chunks
 			 * on the retransmit queue are always kept in order.
 			 */
@@ -1375,6 +1377,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
 				 * instance).
 				 */
 				if (!tchunk->tsn_gap_acked &&
+				    !tchunk->resent &&
 				    tchunk->rtt_in_progress) {
 					tchunk->rtt_in_progress = 0;
 					rtt = jiffies - tchunk->sent_at;