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

[Xufeng Zhang]

From: Signed-off-by: Xufeng Zhang <xufeng.zhang@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
 include/net/sctp/structs.h |    1 +
 net/sctp/output.c          |   23 +++++++++++++----------
 net/sctp/outqueue.c        |    3 +++
 net/sctp/sm_make_chunk.c   |    1 +
 4 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 2174d8d..ea0ca5f 100644
--- a/include/net/sctp/structs.h
+++ b/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? */
diff --git a/net/sctp/output.c b/net/sctp/output.c
index e650978..32c214d 100644
--- a/net/sctp/output.c
+++ b/net/sctp/output.c
@@ -467,17 +467,20 @@ int sctp_packet_transmit(struct sctp_packet *packet)
 	list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
 		list_del_init(&chunk->list);
 		if (sctp_chunk_is_data(chunk)) {
-			/* 6.3.1 C4) When data is in flight and when allowed
-			 * by rule C5, a new RTT measurement MUST be made each
-			 * round trip.  Furthermore, new RTT measurements
-			 * SHOULD be made no more than once per round-trip
-			 * for a given destination transport address.
-			 */
-
-			if (!tp->rto_pending) {
-				chunk->rtt_in_progress = 1;
-				tp->rto_pending = 1;
+			if (!chunk->resent) {
+				/* 6.3.1 C4) When data is in flight and when allowed
+				 * by rule C5, a new RTT measurement MUST be made each
+				 * round trip.  Furthermore, new RTT measurements
+				 * SHOULD be made no more than once per round-trip
+				 * for a given destination transport address.
+				 */
+
+				if (!tp->rto_pending) {
+					chunk->rtt_in_progress = 1;
+					tp->rto_pending = 1;
+				}
 			}
+
 			has_data = 1;
 		}
 
diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
index 94df758..70f4f56 100644
--- a/net/sctp/outqueue.c
+++ b/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;
diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index fe69032..8fe89f8 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -1321,6 +1321,7 @@ struct sctp_chunk *sctp_chunkify(struct sk_buff *skb,
 	INIT_LIST_HEAD(&retval->list);
 	retval->skb		= skb;
 	retval->asoc		= (struct sctp_association *)asoc;
+	retval->resent          = 0;
 	retval->singleton	= 1;
 
 	retval->fast_retransmit = SCTP_CAN_FRTX;
-- 
1.7.0.2

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