net/sctp/transport.c

   1 /* SCTP kernel implementation
   2  * Copyright (c) 1999-2000 Cisco, Inc.
   3  * Copyright (c) 1999-2001 Motorola, Inc.
   4  * Copyright (c) 2001-2003 International Business Machines Corp.
   5  * Copyright (c) 2001 Intel Corp.
   6  * Copyright (c) 2001 La Monte H.P. Yarroll
   7  *
   8  * This file is part of the SCTP kernel implementation
   9  *
  10  * This module provides the abstraction for an SCTP tranport representing
  11  * a remote transport address.  For local transport addresses, we just use
  12  * union sctp_addr.
  13  *
  14  * This SCTP implementation is free software;
  15  * you can redistribute it and/or modify it under the terms of
  16  * the GNU General Public License as published by
  17  * the Free Software Foundation; either version 2, or (at your option)
  18  * any later version.
  19  *
  20  * This SCTP implementation is distributed in the hope that it
  21  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  22  *                 ************************
  23  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  24  * See the GNU General Public License for more details.
  25  *
  26  * You should have received a copy of the GNU General Public License
  27  * along with GNU CC; see the file COPYING.  If not, write to
  28  * the Free Software Foundation, 59 Temple Place - Suite 330,
  29  * Boston, MA 02111-1307, USA.
  30  *
  31  * Please send any bug reports or fixes you make to the
  32  * email address(es):
  33  *    lksctp developers <lksctp-developers@lists.sourceforge.net>
  34  *
  35  * Or submit a bug report through the following website:
  36  *    http://www.sf.net/projects/lksctp
  37  *
  38  * Written or modified by:
  39  *    La Monte H.P. Yarroll <piggy@acm.org>
  40  *    Karl Knutson          <karl@athena.chicago.il.us>
  41  *    Jon Grimm             <jgrimm@us.ibm.com>
  42  *    Xingang Guo           <xingang.guo@intel.com>
  43  *    Hui Huang             <hui.huang@nokia.com>
  44  *    Sridhar Samudrala     <sri@us.ibm.com>
  45  *    Ardelle Fan           <ardelle.fan@intel.com>
  46  *
  47  * Any bugs reported given to us we will try to fix... any fixes shared will
  48  * be incorporated into the next SCTP release.
  49  */
  50
  51 #include <linux/types.h>
  52 #include <linux/random.h>
  53 #include <net/sctp/sctp.h>
  54 #include <net/sctp/sm.h>
  55
  56 /* 1st Level Abstractions.  */
  57
  58 /* Initialize a new transport from provided memory.  */
  59 static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer,
  60                                                   const union sctp_addr *addr,
  61                                                   gfp_t gfp)
  62 {
  63         /* Copy in the address.  */
  64         peer->ipaddr = *addr;
  65         peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
  66         peer->asoc = NULL;
  67
  68         peer->dst = NULL;
  69         memset(&peer->saddr, 0, sizeof(union sctp_addr));
  70
  71         /* From 6.3.1 RTO Calculation:
  72          *
  73          * C1) Until an RTT measurement has been made for a packet sent to the
  74          * given destination transport address, set RTO to the protocol
  75          * parameter 'RTO.Initial'.
  76          */
  77         peer->last_rto = peer->rto = msecs_to_jiffies(sctp_rto_initial);
  78         peer->rtt = 0;
  79         peer->rttvar = 0;
  80         peer->srtt = 0;
  81         peer->rto_pending = 0;
  82
  83         peer->last_time_heard = jiffies;
  84         peer->last_time_used = jiffies;
  85         peer->last_time_ecne_reduced = jiffies;
  86
  87         peer->init_sent_count = 0;
  88
  89         peer->param_flags = SPP_HB_DISABLE |
  90                             SPP_PMTUD_ENABLE |
  91                             SPP_SACKDELAY_ENABLE;
  92         peer->hbinterval  = 0;
  93
  94         /* Initialize the default path max_retrans.  */
  95         peer->pathmaxrxt  = sctp_max_retrans_path;
  96         peer->error_count = 0;
  97
  98         INIT_LIST_HEAD(&peer->transmitted);
  99         INIT_LIST_HEAD(&peer->send_ready);
 100         INIT_LIST_HEAD(&peer->transports);
 101
 102         setup_timer(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event,
 103                         (unsigned long)peer);
 104         setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
 105                         (unsigned long)peer);
 106
 107         /* Initialize the 64-bit random nonce sent with heartbeat. */
 108         get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));
 109
 110         atomic_set(&peer->refcnt, 1);
 111         peer->dead = 0;
 112
 113         peer->malloced = 0;
 114
 115         /* Initialize the state information for SFR-CACC */
 116         peer->cacc.changeover_active = 0;
 117         peer->cacc.cycling_changeover = 0;
 118         peer->cacc.next_tsn_at_change = 0;
 119         peer->cacc.cacc_saw_newack = 0;
 120
 121         return peer;
 122 }
 123
 124 /* Allocate and initialize a new transport.  */
 125 struct sctp_transport *sctp_transport_new(const union sctp_addr *addr,
 126                                           gfp_t gfp)
 127 {
 128         struct sctp_transport *transport;
 129
 130         transport = t_new(struct sctp_transport, gfp);
 131         if (!transport)
 132                 goto fail;
 133
 134         if (!sctp_transport_init(transport, addr, gfp))
 135                 goto fail_init;
 136
 137         transport->malloced = 1;
 138         SCTP_DBG_OBJCNT_INC(transport);
 139
 140         return transport;
 141
 142 fail_init:
 143         kfree(transport);
 144
 145 fail:
 146         return NULL;
 147 }
 148
 149 /* This transport is no longer needed.  Free up if possible, or
 150  * delay until it last reference count.
 151  */
 152 void sctp_transport_free(struct sctp_transport *transport)
 153 {
 154         transport->dead = 1;
 155
 156         /* Try to delete the heartbeat timer.  */
 157         if (del_timer(&transport->hb_timer))
 158                 sctp_transport_put(transport);
 159
 160         /* Delete the T3_rtx timer if it's active.
 161          * There is no point in not doing this now and letting
 162          * structure hang around in memory since we know
 163          * the tranport is going away.
 164          */
 165         if (timer_pending(&transport->T3_rtx_timer) &&
 166             del_timer(&transport->T3_rtx_timer))
 167                 sctp_transport_put(transport);
 168
 169
 170         sctp_transport_put(transport);
 171 }
 172
 173 /* Destroy the transport data structure.
 174  * Assumes there are no more users of this structure.
 175  */
 176 static void sctp_transport_destroy(struct sctp_transport *transport)
 177 {
 178         SCTP_ASSERT(transport->dead, "Transport is not dead", return);
 179
 180         if (transport->asoc)
 181                 sctp_association_put(transport->asoc);
 182
 183         sctp_packet_free(&transport->packet);
 184
 185         dst_release(transport->dst);
 186         kfree(transport);
 187         SCTP_DBG_OBJCNT_DEC(transport);
 188 }
 189
 190 /* Start T3_rtx timer if it is not already running and update the heartbeat
 191  * timer.  This routine is called every time a DATA chunk is sent.
 192  */
 193 void sctp_transport_reset_timers(struct sctp_transport *transport)
 194 {
 195         /* RFC 2960 6.3.2 Retransmission Timer Rules
 196          *
 197          * R1) Every time a DATA chunk is sent to any address(including a
 198          * retransmission), if the T3-rtx timer of that address is not running
 199          * start it running so that it will expire after the RTO of that
 200          * address.
 201          */
 202
 203         if (!timer_pending(&transport->T3_rtx_timer))
 204                 if (!mod_timer(&transport->T3_rtx_timer,
 205                                jiffies + transport->rto))
 206                         sctp_transport_hold(transport);
 207
 208         /* When a data chunk is sent, reset the heartbeat interval.  */
 209         if (!mod_timer(&transport->hb_timer,
 210                        sctp_transport_timeout(transport)))
 211             sctp_transport_hold(transport);
 212 }
 213
 214 /* This transport has been assigned to an association.
 215  * Initialize fields from the association or from the sock itself.
 216  * Register the reference count in the association.
 217  */
 218 void sctp_transport_set_owner(struct sctp_transport *transport,
 219                               struct sctp_association *asoc)
 220 {
 221         transport->asoc = asoc;
 222         sctp_association_hold(asoc);
 223 }
 224
 225 /* Initialize the pmtu of a transport. */
 226 void sctp_transport_pmtu(struct sctp_transport *transport)
 227 {
 228         struct dst_entry *dst;
 229
 230         dst = transport->af_specific->get_dst(NULL, &transport->ipaddr, NULL);
 231
 232         if (dst) {
 233                 transport->pathmtu = dst_mtu(dst);
 234                 dst_release(dst);
 235         } else
 236                 transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 237 }
 238
 239 /* this is a complete rip-off from __sk_dst_check
 240  * the cookie is always 0 since this is how it's used in the
 241  * pmtu code
 242  */
 243 static struct dst_entry *sctp_transport_dst_check(struct sctp_transport *t)
 244 {
 245         struct dst_entry *dst = t->dst;
 246
 247         if (dst && dst->obsolete && dst->ops->check(dst, 0) == NULL) {
 248                 dst_release(t->dst);
 249                 t->dst = NULL;
 250                 return NULL;
 251         }
 252
 253         return dst;
 254 }
 255
 256 void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
 257 {
 258         struct dst_entry *dst;
 259
 260         if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
 261                 printk(KERN_WARNING "%s: Reported pmtu %d too low, "
 262                        "using default minimum of %d\n",
 263                        __FUNCTION__, pmtu,
 264                        SCTP_DEFAULT_MINSEGMENT);
 265                 /* Use default minimum segment size and disable
 266                  * pmtu discovery on this transport.
 267                  */
 268                 t->pathmtu = SCTP_DEFAULT_MINSEGMENT;
 269         } else {
 270                 t->pathmtu = pmtu;
 271         }
 272
 273         dst = sctp_transport_dst_check(t);
 274         if (dst)
 275                 dst->ops->update_pmtu(dst, pmtu);
 276 }
 277
 278 /* Caches the dst entry and source address for a transport's destination
 279  * address.
 280  */
 281 void sctp_transport_route(struct sctp_transport *transport,
 282                           union sctp_addr *saddr, struct sctp_sock *opt)
 283 {
 284         struct sctp_association *asoc = transport->asoc;
 285         struct sctp_af *af = transport->af_specific;
 286         union sctp_addr *daddr = &transport->ipaddr;
 287         struct dst_entry *dst;
 288
 289         dst = af->get_dst(asoc, daddr, saddr);
 290
 291         if (saddr)
 292                 memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
 293         else
 294                 af->get_saddr(asoc, dst, daddr, &transport->saddr);
 295
 296         transport->dst = dst;
 297         if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
 298                 return;
 299         }
 300         if (dst) {
 301                 transport->pathmtu = dst_mtu(dst);
 302
 303                 /* Initialize sk->sk_rcv_saddr, if the transport is the
 304                  * association's active path for getsockname().
 305                  */
 306                 if (asoc && (transport == asoc->peer.active_path))
 307                         opt->pf->af->to_sk_saddr(&transport->saddr,
 308                                                  asoc->base.sk);
 309         } else
 310                 transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 311 }
 312
 313 /* Hold a reference to a transport.  */
 314 void sctp_transport_hold(struct sctp_transport *transport)
 315 {
 316         atomic_inc(&transport->refcnt);
 317 }
 318
 319 /* Release a reference to a transport and clean up
 320  * if there are no more references.
 321  */
 322 void sctp_transport_put(struct sctp_transport *transport)
 323 {
 324         if (atomic_dec_and_test(&transport->refcnt))
 325                 sctp_transport_destroy(transport);
 326 }
 327
 328 /* Update transport's RTO based on the newly calculated RTT. */
 329 void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
 330 {
 331         /* Check for valid transport.  */
 332         SCTP_ASSERT(tp, "NULL transport", return);
 333
 334         /* We should not be doing any RTO updates unless rto_pending is set.  */
 335         SCTP_ASSERT(tp->rto_pending, "rto_pending not set", return);
 336
 337         if (tp->rttvar || tp->srtt) {
 338                 /* 6.3.1 C3) When a new RTT measurement R' is made, set
 339                  * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
 340                  * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
 341                  */
 342
 343                 /* Note:  The above algorithm has been rewritten to
 344                  * express rto_beta and rto_alpha as inverse powers
 345                  * of two.
 346                  * For example, assuming the default value of RTO.Alpha of
 347                  * 1/8, rto_alpha would be expressed as 3.
 348                  */
 349                 tp->rttvar = tp->rttvar - (tp->rttvar >> sctp_rto_beta)
 350                         + ((abs(tp->srtt - rtt)) >> sctp_rto_beta);
 351                 tp->srtt = tp->srtt - (tp->srtt >> sctp_rto_alpha)
 352                         + (rtt >> sctp_rto_alpha);
 353         } else {
 354                 /* 6.3.1 C2) When the first RTT measurement R is made, set
 355                  * SRTT <- R, RTTVAR <- R/2.
 356                  */
 357                 tp->srtt = rtt;
 358                 tp->rttvar = rtt >> 1;
 359         }
 360
 361         /* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
 362          * adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
 363          */
 364         if (tp->rttvar == 0)
 365                 tp->rttvar = SCTP_CLOCK_GRANULARITY;
 366
 367         /* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
 368         tp->rto = tp->srtt + (tp->rttvar << 2);
 369
 370         /* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
 371          * seconds then it is rounded up to RTO.Min seconds.
 372          */
 373         if (tp->rto < tp->asoc->rto_min)
 374                 tp->rto = tp->asoc->rto_min;
 375
 376         /* 6.3.1 C7) A maximum value may be placed on RTO provided it is
 377          * at least RTO.max seconds.
 378          */
 379         if (tp->rto > tp->asoc->rto_max)
 380                 tp->rto = tp->asoc->rto_max;
 381
 382         tp->rtt = rtt;
 383         tp->last_rto = tp->rto;
 384
 385         /* Reset rto_pending so that a new RTT measurement is started when a
 386          * new data chunk is sent.
 387          */
 388         tp->rto_pending = 0;
 389
 390         SCTP_DEBUG_PRINTK("%s: transport: %p, rtt: %d, srtt: %d "
 391                           "rttvar: %d, rto: %ld\n", __FUNCTION__,
 392                           tp, rtt, tp->srtt, tp->rttvar, tp->rto);
 393 }
 394
 395 /* This routine updates the transport's cwnd and partial_bytes_acked
 396  * parameters based on the bytes acked in the received SACK.
 397  */
 398 void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 399                                __u32 sack_ctsn, __u32 bytes_acked)
 400 {
 401         __u32 cwnd, ssthresh, flight_size, pba, pmtu;
 402
 403         cwnd = transport->cwnd;
 404         flight_size = transport->flight_size;
 405
 406         /* The appropriate cwnd increase algorithm is performed if, and only
 407          * if the cumulative TSN has advanced and the congestion window is
 408          * being fully utilized.
 409          */
 410         if ((transport->asoc->ctsn_ack_point >= sack_ctsn) ||
 411             (flight_size < cwnd))
 412                 return;
 413
 414         ssthresh = transport->ssthresh;
 415         pba = transport->partial_bytes_acked;
 416         pmtu = transport->asoc->pathmtu;
 417
 418         if (cwnd <= ssthresh) {
 419                 /* RFC 2960 7.2.1, sctpimpguide-05 2.14.2 When cwnd is less
 420                  * than or equal to ssthresh an SCTP endpoint MUST use the
 421                  * slow start algorithm to increase cwnd only if the current
 422                  * congestion window is being fully utilized and an incoming
 423                  * SACK advances the Cumulative TSN Ack Point. Only when these
 424                  * two conditions are met can the cwnd be increased otherwise
 425                  * the cwnd MUST not be increased. If these conditions are met
 426                  * then cwnd MUST be increased by at most the lesser of
 427                  * 1) the total size of the previously outstanding DATA
 428                  * chunk(s) acknowledged, and 2) the destination's path MTU.
 429                  */
 430                 if (bytes_acked > pmtu)
 431                         cwnd += pmtu;
 432                 else
 433                         cwnd += bytes_acked;
 434                 SCTP_DEBUG_PRINTK("%s: SLOW START: transport: %p, "
 435                                   "bytes_acked: %d, cwnd: %d, ssthresh: %d, "
 436                                   "flight_size: %d, pba: %d\n",
 437                                   __FUNCTION__,
 438                                   transport, bytes_acked, cwnd,
 439                                   ssthresh, flight_size, pba);
 440         } else {
 441                 /* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
 442                  * upon each SACK arrival that advances the Cumulative TSN Ack
 443                  * Point, increase partial_bytes_acked by the total number of
 444                  * bytes of all new chunks acknowledged in that SACK including
 445                  * chunks acknowledged by the new Cumulative TSN Ack and by
 446                  * Gap Ack Blocks.
 447                  *
 448                  * When partial_bytes_acked is equal to or greater than cwnd
 449                  * and before the arrival of the SACK the sender had cwnd or
 450                  * more bytes of data outstanding (i.e., before arrival of the
 451                  * SACK, flightsize was greater than or equal to cwnd),
 452                  * increase cwnd by MTU, and reset partial_bytes_acked to
 453                  * (partial_bytes_acked - cwnd).
 454                  */
 455                 pba += bytes_acked;
 456                 if (pba >= cwnd) {
 457                         cwnd += pmtu;
 458                         pba = ((cwnd < pba) ? (pba - cwnd) : 0);
 459                 }
 460                 SCTP_DEBUG_PRINTK("%s: CONGESTION AVOIDANCE: "
 461                                   "transport: %p, bytes_acked: %d, cwnd: %d, "
 462                                   "ssthresh: %d, flight_size: %d, pba: %d\n",
 463                                   __FUNCTION__,
 464                                   transport, bytes_acked, cwnd,
 465                                   ssthresh, flight_size, pba);
 466         }
 467
 468         transport->cwnd = cwnd;
 469         transport->partial_bytes_acked = pba;
 470 }
 471
 472 /* This routine is used to lower the transport's cwnd when congestion is
 473  * detected.
 474  */
 475 void sctp_transport_lower_cwnd(struct sctp_transport *transport,
 476                                sctp_lower_cwnd_t reason)
 477 {
 478         switch (reason) {
 479         case SCTP_LOWER_CWND_T3_RTX:
 480                 /* RFC 2960 Section 7.2.3, sctpimpguide
 481                  * When the T3-rtx timer expires on an address, SCTP should
 482                  * perform slow start by:
 483                  *      ssthresh = max(cwnd/2, 4*MTU)
 484                  *      cwnd = 1*MTU
 485                  *      partial_bytes_acked = 0
 486                  */
 487                 transport->ssthresh = max(transport->cwnd/2,
 488                                           4*transport->asoc->pathmtu);
 489                 transport->cwnd = transport->asoc->pathmtu;
 490                 break;
 491
 492         case SCTP_LOWER_CWND_FAST_RTX:
 493                 /* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
 494                  * destination address(es) to which the missing DATA chunks
 495                  * were last sent, according to the formula described in
 496                  * Section 7.2.3.
 497                  *
 498                  * RFC 2960 7.2.3, sctpimpguide Upon detection of packet
 499                  * losses from SACK (see Section 7.2.4), An endpoint
 500                  * should do the following:
 501                  *      ssthresh = max(cwnd/2, 4*MTU)
 502                  *      cwnd = ssthresh
 503                  *      partial_bytes_acked = 0
 504                  */
 505                 transport->ssthresh = max(transport->cwnd/2,
 506                                           4*transport->asoc->pathmtu);
 507                 transport->cwnd = transport->ssthresh;
 508                 break;
 509
 510         case SCTP_LOWER_CWND_ECNE:
 511                 /* RFC 2481 Section 6.1.2.
 512                  * If the sender receives an ECN-Echo ACK packet
 513                  * then the sender knows that congestion was encountered in the
 514                  * network on the path from the sender to the receiver. The
 515                  * indication of congestion should be treated just as a
 516                  * congestion loss in non-ECN Capable TCP. That is, the TCP
 517                  * source halves the congestion window "cwnd" and reduces the
 518                  * slow start threshold "ssthresh".
 519                  * A critical condition is that TCP does not react to
 520                  * congestion indications more than once every window of
 521                  * data (or more loosely more than once every round-trip time).
 522                  */
 523                 if ((jiffies - transport->last_time_ecne_reduced) >
 524                     transport->rtt) {
 525                         transport->ssthresh = max(transport->cwnd/2,
 526                                                   4*transport->asoc->pathmtu);
 527                         transport->cwnd = transport->ssthresh;
 528                         transport->last_time_ecne_reduced = jiffies;
 529                 }
 530                 break;
 531
 532         case SCTP_LOWER_CWND_INACTIVE:
 533                 /* RFC 2960 Section 7.2.1, sctpimpguide
 534                  * When the endpoint does not transmit data on a given
 535                  * transport address, the cwnd of the transport address
 536                  * should be adjusted to max(cwnd/2, 4*MTU) per RTO.
 537                  * NOTE: Although the draft recommends that this check needs
 538                  * to be done every RTO interval, we do it every hearbeat
 539                  * interval.
 540                  */
 541                 if ((jiffies - transport->last_time_used) > transport->rto)
 542                         transport->cwnd = max(transport->cwnd/2,
 543                                                  4*transport->asoc->pathmtu);
 544                 break;
 545         }
 546
 547         transport->partial_bytes_acked = 0;
 548         SCTP_DEBUG_PRINTK("%s: transport: %p reason: %d cwnd: "
 549                           "%d ssthresh: %d\n", __FUNCTION__,
 550                           transport, reason,
 551                           transport->cwnd, transport->ssthresh);
 552 }
 553
 554 /* What is the next timeout value for this transport? */
 555 unsigned long sctp_transport_timeout(struct sctp_transport *t)
 556 {
 557         unsigned long timeout;
 558         timeout = t->rto + sctp_jitter(t->rto);
 559         if (t->state != SCTP_UNCONFIRMED)
 560                 timeout += t->hbinterval;
 561         timeout += jiffies;
 562         return timeout;
 563 }
 564
 565 /* Reset transport variables to their initial values */
 566 void sctp_transport_reset(struct sctp_transport *t)
 567 {
 568         struct sctp_association *asoc = t->asoc;
 569
 570         /* RFC 2960 (bis), Section 5.2.4
 571          * All the congestion control parameters (e.g., cwnd, ssthresh)
 572          * related to this peer MUST be reset to their initial values
 573          * (see Section 6.2.1)
 574          */
 575         t->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));
 576         t->ssthresh = asoc->peer.i.a_rwnd;
 577         t->last_rto = t->rto = asoc->rto_initial;
 578         t->rtt = 0;
 579         t->srtt = 0;
 580         t->rttvar = 0;
 581
 582         /* Reset these additional varibles so that we have a clean
 583          * slate.
 584          */
 585         t->partial_bytes_acked = 0;
 586         t->flight_size = 0;
 587         t->error_count = 0;
 588         t->rto_pending = 0;
 589
 590         /* Initialize the state information for SFR-CACC */
 591         t->cacc.changeover_active = 0;
 592         t->cacc.cycling_changeover = 0;
 593         t->cacc.next_tsn_at_change = 0;
 594         t->cacc.cacc_saw_newack = 0;
 595 }