/* SCTP kernel implementation

   * Copyright (c) 1999-2000 Cisco, Inc.
   * Copyright (c) 1999-2001 Motorola, Inc.
   * Copyright (c) 2001-2003 International Business Machines Corp.
   * Copyright (c) 2001 Intel Corp.
   * Copyright (c) 2001 La Monte H.P. Yarroll
   *

   * This file is part of the SCTP kernel implementation

   *
   * This module provides the abstraction for an SCTP tranport representing
   * a remote transport address.  For local transport addresses, we just use
   * union sctp_addr.
   *

   * This SCTP implementation is free software;

   * you can redistribute it and/or modify it under the terms of
   * the GNU General Public License as published by
   * the Free Software Foundation; either version 2, or (at your option)
   * any later version.
   *

   * This SCTP implementation is distributed in the hope that it

   * will be useful, but WITHOUT ANY WARRANTY; without even the implied
   *                 ************************
   * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   * See the GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with GNU CC; see the file COPYING.  If not, write to
   * the Free Software Foundation, 59 Temple Place - Suite 330,
   * Boston, MA 02111-1307, USA.
   *
   * Please send any bug reports or fixes you make to the
   * email address(es):
   *    lksctp developers <lksctp-developers@lists.sourceforge.net>
   *
   * Or submit a bug report through the following website:
   *    http://www.sf.net/projects/lksctp
   *
   * Written or modified by:
   *    La Monte H.P. Yarroll <piggy@acm.org>
   *    Karl Knutson          <karl@athena.chicago.il.us>
   *    Jon Grimm             <jgrimm@us.ibm.com>
   *    Xingang Guo           <xingang.guo@intel.com>
   *    Hui Huang             <hui.huang@nokia.com>
   *    Sridhar Samudrala	    <sri@us.ibm.com>
   *    Ardelle Fan	    <ardelle.fan@intel.com>
   *
   * Any bugs reported given to us we will try to fix... any fixes shared will
   * be incorporated into the next SCTP release.
   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/slab.h>

  #include <linux/types.h>

  #include <linux/random.h>

  #include <net/sctp/sctp.h>
  #include <net/sctp/sm.h>
  
  /* 1st Level Abstractions.  */
  
  /* Initialize a new transport from provided memory.  */
  static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer,
  						  const union sctp_addr *addr,

  						  gfp_t gfp)

  {
  	/* Copy in the address.  */
  	peer->ipaddr = *addr;
  	peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);

  	memset(&peer->saddr, 0, sizeof(union sctp_addr));
  
  	/* From 6.3.1 RTO Calculation:
  	 *
  	 * C1) Until an RTT measurement has been made for a packet sent to the
  	 * given destination transport address, set RTO to the protocol
  	 * parameter 'RTO.Initial'.
  	 */

  	peer->rto = msecs_to_jiffies(sctp_rto_initial);

  
  	peer->last_time_heard = jiffies;

  	peer->last_time_ecne_reduced = jiffies;

  	peer->param_flags = SPP_HB_DISABLE |
  			    SPP_PMTUD_ENABLE |
  			    SPP_SACKDELAY_ENABLE;

  
  	/* Initialize the default path max_retrans.  */

  	peer->pathmaxrxt  = sctp_max_retrans_path;

  
  	INIT_LIST_HEAD(&peer->transmitted);
  	INIT_LIST_HEAD(&peer->send_ready);
  	INIT_LIST_HEAD(&peer->transports);

  	setup_timer(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event,
  			(unsigned long)peer);
  	setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
  			(unsigned long)peer);

  	setup_timer(&peer->proto_unreach_timer,
  		    sctp_generate_proto_unreach_event, (unsigned long)peer);

  	/* Initialize the 64-bit random nonce sent with heartbeat. */
  	get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));

  	atomic_set(&peer->refcnt, 1);

  
  	return peer;
  }
  
  /* Allocate and initialize a new transport.  */

  struct sctp_transport *sctp_transport_new(const union sctp_addr *addr,

  					  gfp_t gfp)

  {

  	struct sctp_transport *transport;

  	transport = t_new(struct sctp_transport, gfp);

  	if (!transport)
  		goto fail;
  
  	if (!sctp_transport_init(transport, addr, gfp))
  		goto fail_init;
  
  	transport->malloced = 1;
  	SCTP_DBG_OBJCNT_INC(transport);
  
  	return transport;
  
  fail_init:
  	kfree(transport);
  
  fail:
  	return NULL;
  }
  
  /* This transport is no longer needed.  Free up if possible, or
   * delay until it last reference count.
   */
  void sctp_transport_free(struct sctp_transport *transport)
  {
  	transport->dead = 1;
  
  	/* Try to delete the heartbeat timer.  */
  	if (del_timer(&transport->hb_timer))
  		sctp_transport_put(transport);
  
  	/* Delete the T3_rtx timer if it's active.
  	 * There is no point in not doing this now and letting
  	 * structure hang around in memory since we know
  	 * the tranport is going away.
  	 */
  	if (timer_pending(&transport->T3_rtx_timer) &&
  	    del_timer(&transport->T3_rtx_timer))
  		sctp_transport_put(transport);

  	/* Delete the ICMP proto unreachable timer if it's active. */
  	if (timer_pending(&transport->proto_unreach_timer) &&
  	    del_timer(&transport->proto_unreach_timer))
  		sctp_association_put(transport->asoc);

  
  	sctp_transport_put(transport);
  }
  
  /* Destroy the transport data structure.
   * Assumes there are no more users of this structure.
   */
  static void sctp_transport_destroy(struct sctp_transport *transport)
  {
  	SCTP_ASSERT(transport->dead, "Transport is not dead", return);
  
  	if (transport->asoc)
  		sctp_association_put(transport->asoc);

  	sctp_packet_free(&transport->packet);

  
  	dst_release(transport->dst);
  	kfree(transport);
  	SCTP_DBG_OBJCNT_DEC(transport);
  }
  
  /* Start T3_rtx timer if it is not already running and update the heartbeat
   * timer.  This routine is called every time a DATA chunk is sent.
   */

  void sctp_transport_reset_timers(struct sctp_transport *transport)

  {
  	/* RFC 2960 6.3.2 Retransmission Timer Rules
  	 *
  	 * R1) Every time a DATA chunk is sent to any address(including a
  	 * retransmission), if the T3-rtx timer of that address is not running
  	 * start it running so that it will expire after the RTO of that
  	 * address.
  	 */

  	if (!timer_pending(&transport->T3_rtx_timer))

  		if (!mod_timer(&transport->T3_rtx_timer,
  			       jiffies + transport->rto))
  			sctp_transport_hold(transport);
  
  	/* When a data chunk is sent, reset the heartbeat interval.  */
  	if (!mod_timer(&transport->hb_timer,
  		       sctp_transport_timeout(transport)))
  	    sctp_transport_hold(transport);
  }
  
  /* This transport has been assigned to an association.
   * Initialize fields from the association or from the sock itself.
   * Register the reference count in the association.
   */
  void sctp_transport_set_owner(struct sctp_transport *transport,
  			      struct sctp_association *asoc)
  {
  	transport->asoc = asoc;
  	sctp_association_hold(asoc);
  }
  
  /* Initialize the pmtu of a transport. */

  void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)

  {

  	/* If we don't have a fresh route, look one up */
  	if (!transport->dst || transport->dst->obsolete > 1) {
  		dst_release(transport->dst);
  		transport->af_specific->get_dst(transport, &transport->saddr,

  						&transport->fl, sk);

  	}

  	if (transport->dst) {
  		transport->pathmtu = dst_mtu(transport->dst);

  	} else

  		transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;

  }

  /* this is a complete rip-off from __sk_dst_check
   * the cookie is always 0 since this is how it's used in the
   * pmtu code
   */
  static struct dst_entry *sctp_transport_dst_check(struct sctp_transport *t)
  {
  	struct dst_entry *dst = t->dst;
  
  	if (dst && dst->obsolete && dst->ops->check(dst, 0) == NULL) {
  		dst_release(t->dst);
  		t->dst = NULL;
  		return NULL;
  	}
  
  	return dst;
  }
  
  void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
  {
  	struct dst_entry *dst;
  
  	if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {

  		pr_warn("%s: Reported pmtu %d too low, using default minimum of %d
  ",
  			__func__, pmtu,
  			SCTP_DEFAULT_MINSEGMENT);

  		/* Use default minimum segment size and disable
  		 * pmtu discovery on this transport.
  		 */
  		t->pathmtu = SCTP_DEFAULT_MINSEGMENT;

  	} else {
  		t->pathmtu = pmtu;
  	}
  
  	dst = sctp_transport_dst_check(t);
  	if (dst)
  		dst->ops->update_pmtu(dst, pmtu);
  }

  /* Caches the dst entry and source address for a transport's destination
   * address.
   */
  void sctp_transport_route(struct sctp_transport *transport,
  			  union sctp_addr *saddr, struct sctp_sock *opt)
  {
  	struct sctp_association *asoc = transport->asoc;
  	struct sctp_af *af = transport->af_specific;

  	af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));

  
  	if (saddr)
  		memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
  	else

  		af->get_saddr(opt, transport, &transport->fl);

  	if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
  		return;
  	}

  	if (transport->dst) {
  		transport->pathmtu = dst_mtu(transport->dst);

  
  		/* Initialize sk->sk_rcv_saddr, if the transport is the
  		 * association's active path for getsockname().

  		 */

  		if (asoc && (!asoc->peer.primary_path ||
  				(transport == asoc->peer.active_path)))

  			opt->pf->af->to_sk_saddr(&transport->saddr,
  						 asoc->base.sk);

  	} else

  		transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;

  }
  
  /* Hold a reference to a transport.  */
  void sctp_transport_hold(struct sctp_transport *transport)
  {
  	atomic_inc(&transport->refcnt);
  }
  
  /* Release a reference to a transport and clean up
   * if there are no more references.
   */
  void sctp_transport_put(struct sctp_transport *transport)
  {
  	if (atomic_dec_and_test(&transport->refcnt))
  		sctp_transport_destroy(transport);
  }
  
  /* Update transport's RTO based on the newly calculated RTT. */
  void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
  {
  	/* Check for valid transport.  */
  	SCTP_ASSERT(tp, "NULL transport", return);
  
  	/* We should not be doing any RTO updates unless rto_pending is set.  */
  	SCTP_ASSERT(tp->rto_pending, "rto_pending not set", return);
  
  	if (tp->rttvar || tp->srtt) {
  		/* 6.3.1 C3) When a new RTT measurement R' is made, set
  		 * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
  		 * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
  		 */
  
  		/* Note:  The above algorithm has been rewritten to
  		 * express rto_beta and rto_alpha as inverse powers
  		 * of two.
  		 * For example, assuming the default value of RTO.Alpha of
  		 * 1/8, rto_alpha would be expressed as 3.
  		 */
  		tp->rttvar = tp->rttvar - (tp->rttvar >> sctp_rto_beta)
  			+ ((abs(tp->srtt - rtt)) >> sctp_rto_beta);
  		tp->srtt = tp->srtt - (tp->srtt >> sctp_rto_alpha)
  			+ (rtt >> sctp_rto_alpha);
  	} else {
  		/* 6.3.1 C2) When the first RTT measurement R is made, set
  		 * SRTT <- R, RTTVAR <- R/2.
  		 */
  		tp->srtt = rtt;
  		tp->rttvar = rtt >> 1;
  	}
  
  	/* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
  	 * adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
  	 */
  	if (tp->rttvar == 0)
  		tp->rttvar = SCTP_CLOCK_GRANULARITY;
  
  	/* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
  	tp->rto = tp->srtt + (tp->rttvar << 2);
  
  	/* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
  	 * seconds then it is rounded up to RTO.Min seconds.
  	 */
  	if (tp->rto < tp->asoc->rto_min)
  		tp->rto = tp->asoc->rto_min;
  
  	/* 6.3.1 C7) A maximum value may be placed on RTO provided it is
  	 * at least RTO.max seconds.
  	 */
  	if (tp->rto > tp->asoc->rto_max)
  		tp->rto = tp->asoc->rto_max;
  
  	tp->rtt = rtt;
  
  	/* Reset rto_pending so that a new RTT measurement is started when a
  	 * new data chunk is sent.
  	 */
  	tp->rto_pending = 0;
  
  	SCTP_DEBUG_PRINTK("%s: transport: %p, rtt: %d, srtt: %d "

  			  "rttvar: %d, rto: %ld
  ", __func__,

  			  tp, rtt, tp->srtt, tp->rttvar, tp->rto);
  }
  
  /* This routine updates the transport's cwnd and partial_bytes_acked
   * parameters based on the bytes acked in the received SACK.
   */
  void sctp_transport_raise_cwnd(struct sctp_transport *transport,
  			       __u32 sack_ctsn, __u32 bytes_acked)
  {

  	struct sctp_association *asoc = transport->asoc;

  	__u32 cwnd, ssthresh, flight_size, pba, pmtu;
  
  	cwnd = transport->cwnd;
  	flight_size = transport->flight_size;

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

  	if (asoc->fast_recovery &&
  	    TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
  		asoc->fast_recovery = 0;

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

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

  	 * being fully utilized.
  	 */

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

  	    (flight_size < cwnd))
  		return;
  
  	ssthresh = transport->ssthresh;
  	pba = transport->partial_bytes_acked;

  	pmtu = transport->asoc->pathmtu;

  
  	if (cwnd <= ssthresh) {

  		/* 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 (asoc->fast_recovery)

  			return;

  		if (bytes_acked > pmtu)
  			cwnd += pmtu;
  		else
  			cwnd += bytes_acked;
  		SCTP_DEBUG_PRINTK("%s: SLOW START: transport: %p, "
  				  "bytes_acked: %d, cwnd: %d, ssthresh: %d, "
  				  "flight_size: %d, pba: %d
  ",

  				  __func__,

  				  transport, bytes_acked, cwnd,
  				  ssthresh, flight_size, pba);
  	} else {
  		/* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
  		 * upon each SACK arrival that advances the Cumulative TSN Ack
  		 * Point, increase partial_bytes_acked by the total number of
  		 * bytes of all new chunks acknowledged in that SACK including
  		 * 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).
  		 */
  		pba += bytes_acked;
  		if (pba >= cwnd) {
  			cwnd += pmtu;
  			pba = ((cwnd < pba) ? (pba - cwnd) : 0);
  		}
  		SCTP_DEBUG_PRINTK("%s: CONGESTION AVOIDANCE: "
  				  "transport: %p, bytes_acked: %d, cwnd: %d, "
  				  "ssthresh: %d, flight_size: %d, pba: %d
  ",

  				  __func__,

  				  transport, bytes_acked, cwnd,
  				  ssthresh, flight_size, pba);
  	}
  
  	transport->cwnd = cwnd;
  	transport->partial_bytes_acked = pba;
  }
  
  /* This routine is used to lower the transport's cwnd when congestion is
   * detected.
   */
  void sctp_transport_lower_cwnd(struct sctp_transport *transport,
  			       sctp_lower_cwnd_t reason)
  {

  	struct sctp_association *asoc = transport->asoc;

  	switch (reason) {
  	case SCTP_LOWER_CWND_T3_RTX:
  		/* RFC 2960 Section 7.2.3, sctpimpguide
  		 * When the T3-rtx timer expires on an address, SCTP should
  		 * perform slow start by:
  		 *      ssthresh = max(cwnd/2, 4*MTU)
  		 *      cwnd = 1*MTU
  		 *      partial_bytes_acked = 0
  		 */
  		transport->ssthresh = max(transport->cwnd/2,

  					  4*asoc->pathmtu);
  		transport->cwnd = asoc->pathmtu;

  		/* T3-rtx also clears fast recovery */
  		asoc->fast_recovery = 0;

  		break;
  
  	case SCTP_LOWER_CWND_FAST_RTX:
  		/* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
  		 * destination address(es) to which the missing DATA chunks
  		 * were last sent, according to the formula described in
  		 * Section 7.2.3.

  		 *
  		 * RFC 2960 7.2.3, sctpimpguide Upon detection of packet

  		 * losses from SACK (see Section 7.2.4), An endpoint
  		 * should do the following:
  		 *      ssthresh = max(cwnd/2, 4*MTU)
  		 *      cwnd = ssthresh
  		 *      partial_bytes_acked = 0
  		 */

  		if (asoc->fast_recovery)

  			return;
  
  		/* Mark Fast recovery */

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

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

  					  4*asoc->pathmtu);

  		transport->cwnd = transport->ssthresh;
  		break;
  
  	case SCTP_LOWER_CWND_ECNE:
  		/* RFC 2481 Section 6.1.2.
  		 * If the sender receives an ECN-Echo ACK packet
  		 * then the sender knows that congestion was encountered in the
  		 * network on the path from the sender to the receiver. The
  		 * indication of congestion should be treated just as a
  		 * congestion loss in non-ECN Capable TCP. That is, the TCP
  		 * source halves the congestion window "cwnd" and reduces the
  		 * slow start threshold "ssthresh".
  		 * A critical condition is that TCP does not react to
  		 * congestion indications more than once every window of
  		 * data (or more loosely more than once every round-trip time).
  		 */

  		if (time_after(jiffies, transport->last_time_ecne_reduced +
  					transport->rtt)) {

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

  						  4*asoc->pathmtu);

  			transport->cwnd = transport->ssthresh;
  			transport->last_time_ecne_reduced = jiffies;
  		}
  		break;
  
  	case SCTP_LOWER_CWND_INACTIVE:
  		/* RFC 2960 Section 7.2.1, sctpimpguide
  		 * When the endpoint does not transmit data on a given
  		 * transport address, the cwnd of the transport address
  		 * should be adjusted to max(cwnd/2, 4*MTU) per RTO.
  		 * NOTE: Although the draft recommends that this check needs
  		 * to be done every RTO interval, we do it every hearbeat
  		 * interval.
  		 */

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

  					 4*asoc->pathmtu);

  		break;

  	}

  
  	transport->partial_bytes_acked = 0;
  	SCTP_DEBUG_PRINTK("%s: transport: %p reason: %d cwnd: "

  			  "%d ssthresh: %d
  ", __func__,

  			  transport, reason,
  			  transport->cwnd, transport->ssthresh);
  }

  /* Apply Max.Burst limit to the congestion window:
   * sctpimpguide-05 2.14.2
   * D) When the time comes for the sender to
   * transmit new DATA chunks, the protocol parameter Max.Burst MUST
   * first be applied to limit how many new DATA chunks may be sent.
   * The limit is applied by adjusting cwnd as follows:
   * 	if ((flightsize+ Max.Burst * MTU) < cwnd)
   * 		cwnd = flightsize + Max.Burst * MTU
   */
  
  void sctp_transport_burst_limited(struct sctp_transport *t)
  {
  	struct sctp_association *asoc = t->asoc;
  	u32 old_cwnd = t->cwnd;
  	u32 max_burst_bytes;
  
  	if (t->burst_limited)
  		return;
  
  	max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);
  	if (max_burst_bytes < old_cwnd) {
  		t->cwnd = max_burst_bytes;
  		t->burst_limited = old_cwnd;
  	}
  }
  
  /* Restore the old cwnd congestion window, after the burst had it's
   * desired effect.
   */
  void sctp_transport_burst_reset(struct sctp_transport *t)
  {
  	if (t->burst_limited) {
  		t->cwnd = t->burst_limited;
  		t->burst_limited = 0;
  	}
  }

  /* What is the next timeout value for this transport? */
  unsigned long sctp_transport_timeout(struct sctp_transport *t)
  {
  	unsigned long timeout;

  	timeout = t->rto + sctp_jitter(t->rto);
  	if (t->state != SCTP_UNCONFIRMED)
  		timeout += t->hbinterval;

  	timeout += jiffies;
  	return timeout;
  }

  
  /* Reset transport variables to their initial values */
  void sctp_transport_reset(struct sctp_transport *t)
  {
  	struct sctp_association *asoc = t->asoc;
  
  	/* RFC 2960 (bis), Section 5.2.4
  	 * All the congestion control parameters (e.g., cwnd, ssthresh)
  	 * related to this peer MUST be reset to their initial values
  	 * (see Section 6.2.1)
  	 */
  	t->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));

  	t->burst_limited = 0;

  	t->ssthresh = asoc->peer.i.a_rwnd;

  	t->rto = asoc->rto_initial;

  	t->rtt = 0;
  	t->srtt = 0;
  	t->rttvar = 0;
  
  	/* Reset these additional varibles so that we have a clean
  	 * slate.
  	 */
  	t->partial_bytes_acked = 0;
  	t->flight_size = 0;
  	t->error_count = 0;
  	t->rto_pending = 0;

  	t->hb_sent = 0;

  
  	/* Initialize the state information for SFR-CACC */
  	t->cacc.changeover_active = 0;
  	t->cacc.cycling_changeover = 0;
  	t->cacc.next_tsn_at_change = 0;
  	t->cacc.cacc_saw_newack = 0;
  }

  
  /* Schedule retransmission on the given transport */
  void sctp_transport_immediate_rtx(struct sctp_transport *t)
  {
  	/* Stop pending T3_rtx_timer */
  	if (timer_pending(&t->T3_rtx_timer)) {
  		(void)del_timer(&t->T3_rtx_timer);
  		sctp_transport_put(t);
  	}
  	sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
  	if (!timer_pending(&t->T3_rtx_timer)) {
  		if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
  			sctp_transport_hold(t);
  	}
  	return;
  }