Commit d0b53f40 authored by Marcelo Ricardo Leitner's avatar Marcelo Ricardo Leitner Committed by David S. Miller
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sctp: update order of adjustments of partial_bytes_acked and cwnd 

RFC4960 Errata 3.12 says RFC4960 is unclear about the order of
adjustments applied to partial_bytes_acked and cwnd in the congestion
avoidance phase, and that the actual order should be:
partial_bytes_acked is reset to (partial_bytes_acked - cwnd). Next, cwnd
is increased by MTU.

We were first increasing cwnd, and then subtracting the new value pba,
which leads to a different result as pba is smaller than what it should
and could cause cwnd to not grow as much.

See-also: https://tools.ietf.org/html/draft-ietf-tsvwg-rfc4960-errata-01#section-3.12


Signed-off-by: default avatarMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f3ecab38

net/sctp/transport.c

+8 −7
Original line number Diff line number Diff line
@@ -452,17 +452,18 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport, 
		 * chunks acknowledged by the new Cumulative TSN Ack and by

		 * Gap Ack Blocks.

		 *

		 * When partial_bytes_acked is equal to or greater than cwnd

		 * and before the arrival of the SACK the sender had cwnd or

		 * more bytes of data outstanding (i.e., before arrival of the

		 * SACK, flightsize was greater than or equal to cwnd),

		 * increase cwnd by MTU, and reset partial_bytes_acked to

		 * (partial_bytes_acked - cwnd).

		 * When partial_bytes_acked is equal to or greater than

		 * cwnd and before the arrival of the SACK the sender

		 * had cwnd or more bytes of data outstanding (i.e.,

		 * before arrival of the SACK, flightsize was greater

		 * than or equal to cwnd), partial_bytes_acked is reset

		 * to (partial_bytes_acked - cwnd). Next, cwnd is

		 * increased by MTU. (RFC 4960 Errata 3.12)

		 */

		pba += bytes_acked;

		if (pba >= cwnd) {

			pba = pba - cwnd;

			cwnd += pmtu;

			pba = ((cwnd < pba) ? (pba - cwnd) : 0);

		}



		pr_debug("%s: congestion avoidance: transport:%p, "