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Commit a6465234 authored by Vlad Yasevich's avatar Vlad Yasevich Committed by David S. Miller
Browse files

sctp: Correctly implement Fast Recovery cwnd manipulations. 



Correctly keep track of Fast Recovery state and do not reduce
congestion window multiple times during sucht state.

Signed-off-by: default avatarVlad Yasevich <vladislav.yasevich@hp.com>
Tested-by: default avatarWei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 159c6bea

include/net/sctp/structs.h

+7 −1
Original line number Diff line number Diff line
@@ -902,7 +902,10 @@ struct sctp_transport { 
	 *		calculation completes (i.e. the DATA chunk

	 *		is SACK'd) clear this flag.

	 */

	int rto_pending;

	__u8 rto_pending;



	/* Flag to track the current fast recovery state */

	__u8 fast_recovery;



	/*

	 * These are the congestion stats.
@@ -921,6 +924,9 @@ struct sctp_transport { 
	/* Data that has been sent, but not acknowledged. */

	__u32 flight_size;



	/* TSN marking the fast recovery exit point */

	__u32 fast_recovery_exit;



	/* Destination */

	struct dst_entry *dst;

	/* Source address. */

net/sctp/transport.c

+32 −12
Original line number Diff line number Diff line
@@ -79,6 +79,7 @@ static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer, 
	peer->rttvar = 0;

	peer->srtt = 0;

	peer->rto_pending = 0;

	peer->fast_recovery = 0;



	peer->last_time_heard = jiffies;

	peer->last_time_used = jiffies;
@@ -403,11 +404,16 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport, 
	cwnd = transport->cwnd;

	flight_size = transport->flight_size;



	/* See if we need to exit Fast Recovery first */

	if (transport->fast_recovery &&

	    TSN_lte(transport->fast_recovery_exit, sack_ctsn))

		transport->fast_recovery = 0;



	/* The appropriate cwnd increase algorithm is performed if, and only

	 * if the cumulative TSN has advanced and the congestion window is

	 * if the cumulative TSN whould advanced and the congestion window is

	 * being fully utilized.

	 */

	if ((transport->asoc->ctsn_ack_point >= sack_ctsn) ||

	if (TSN_lte(sack_ctsn, transport->asoc->ctsn_ack_point) ||

	    (flight_size < cwnd))

		return;
@@ -416,17 +422,23 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport, 
	pmtu = transport->asoc->pathmtu;



	if (cwnd <= ssthresh) {

		/* RFC 2960 7.2.1, sctpimpguide-05 2.14.2 When cwnd is less

		 * than or equal to ssthresh an SCTP endpoint MUST use the

		 * slow start algorithm to increase cwnd only if the current

		 * congestion window is being fully utilized and an incoming

		 * SACK advances the Cumulative TSN Ack Point. Only when these

		 * two conditions are met can the cwnd be increased otherwise

		 * the cwnd MUST not be increased. If these conditions are met

		 * then cwnd MUST be increased by at most the lesser of

		 * 1) the total size of the previously outstanding DATA

		 * chunk(s) acknowledged, and 2) the destination's path MTU.

		/* RFC 4960 7.2.1

		 * o  When cwnd is less than or equal to ssthresh, an SCTP

		 *    endpoint MUST use the slow-start algorithm to increase

		 *    cwnd only if the current congestion window is being fully

		 *    utilized, an incoming SACK advances the Cumulative TSN

		 *    Ack Point, and the data sender is not in Fast Recovery.

		 *    Only when these three conditions are met can the cwnd be

		 *    increased; otherwise, the cwnd MUST not be increased.

		 *    If these conditions are met, then cwnd MUST be increased

		 *    by, at most, the lesser of 1) the total size of the

		 *    previously outstanding DATA chunk(s) acknowledged, and

		 *    2) the destination's path MTU.  This upper bound protects

		 *    against the ACK-Splitting attack outlined in [SAVAGE99].

		 */

		if (transport->fast_recovery)

			return;



		if (bytes_acked > pmtu)

			cwnd += pmtu;

		else
@@ -502,6 +514,13 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport, 
		 *      cwnd = ssthresh

		 *      partial_bytes_acked = 0

		 */

		if (transport->fast_recovery)

			return;



		/* Mark Fast recovery */

		transport->fast_recovery = 1;

		transport->fast_recovery_exit = transport->asoc->next_tsn - 1;



		transport->ssthresh = max(transport->cwnd/2,

					  4*transport->asoc->pathmtu);

		transport->cwnd = transport->ssthresh;
@@ -586,6 +605,7 @@ void sctp_transport_reset(struct sctp_transport *t) 
	t->flight_size = 0;

	t->error_count = 0;

	t->rto_pending = 0;

	t->fast_recovery = 0;



	/* Initialize the state information for SFR-CACC */

	t->cacc.changeover_active = 0;