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-rw-r--r--net/sctp/transport.c338
1 files changed, 199 insertions, 139 deletions
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index d9f8af852b5..7dd672fa651 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -24,16 +24,12 @@
* 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.
+ * along with GNU CC; see the file COPYING. If not, see
+ * <http://www.gnu.org/licenses/>.
*
* 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
+ * lksctp developers <linux-sctp@vger.kernel.org>
*
* Written or modified by:
* La Monte H.P. Yarroll <piggy@acm.org>
@@ -43,11 +39,11 @@
* 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>
@@ -56,44 +52,36 @@
/* 1st Level Abstractions. */
/* Initialize a new transport from provided memory. */
-static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer,
+static struct sctp_transport *sctp_transport_init(struct net *net,
+ 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);
- peer->asoc = NULL;
-
- peer->dst = NULL;
memset(&peer->saddr, 0, sizeof(union sctp_addr));
+ peer->sack_generation = 0;
+
/* 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->last_rto = peer->rto = msecs_to_jiffies(sctp_rto_initial);
- peer->rtt = 0;
- peer->rttvar = 0;
- peer->srtt = 0;
- peer->rto_pending = 0;
-
- peer->last_time_heard = jiffies;
- peer->last_time_used = jiffies;
- peer->last_time_ecne_reduced = jiffies;
+ peer->rto = msecs_to_jiffies(net->sctp.rto_initial);
- peer->init_sent_count = 0;
+ peer->last_time_heard = ktime_get();
+ peer->last_time_ecne_reduced = jiffies;
peer->param_flags = SPP_HB_DISABLE |
SPP_PMTUD_ENABLE |
SPP_SACKDELAY_ENABLE;
- peer->hbinterval = 0;
/* Initialize the default path max_retrans. */
- peer->pathmaxrxt = sctp_max_retrans_path;
- peer->error_count = 0;
+ peer->pathmaxrxt = net->sctp.max_retrans_path;
+ peer->pf_retrans = net->sctp.pf_retrans;
INIT_LIST_HEAD(&peer->transmitted);
INIT_LIST_HEAD(&peer->send_ready);
@@ -103,38 +91,31 @@ static struct sctp_transport *sctp_transport_init(struct sctp_transport *peer,
(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);
- peer->dead = 0;
-
- peer->malloced = 0;
-
- /* Initialize the state information for SFR-CACC */
- peer->cacc.changeover_active = 0;
- peer->cacc.cycling_changeover = 0;
- peer->cacc.next_tsn_at_change = 0;
- peer->cacc.cacc_saw_newack = 0;
return peer;
}
/* Allocate and initialize a new transport. */
-struct sctp_transport *sctp_transport_new(const union sctp_addr *addr,
+struct sctp_transport *sctp_transport_new(struct net *net,
+ const union sctp_addr *addr,
gfp_t gfp)
{
struct sctp_transport *transport;
- transport = t_new(struct sctp_transport, gfp);
+ transport = kzalloc(sizeof(*transport), gfp);
if (!transport)
goto fail;
- if (!sctp_transport_init(transport, addr, gfp))
+ if (!sctp_transport_init(net, transport, addr, gfp))
goto fail_init;
- transport->malloced = 1;
SCTP_DBG_OBJCNT_INC(transport);
return transport;
@@ -162,29 +143,43 @@ void sctp_transport_free(struct sctp_transport *transport)
* 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))
+ if (del_timer(&transport->T3_rtx_timer))
sctp_transport_put(transport);
+ /* Delete the ICMP proto unreachable timer if it's active. */
+ if (del_timer(&transport->proto_unreach_timer))
+ sctp_association_put(transport->asoc);
sctp_transport_put(transport);
}
+static void sctp_transport_destroy_rcu(struct rcu_head *head)
+{
+ struct sctp_transport *transport;
+
+ transport = container_of(head, struct sctp_transport, rcu);
+
+ dst_release(transport->dst);
+ kfree(transport);
+ SCTP_DBG_OBJCNT_DEC(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 (unlikely(!transport->dead)) {
+ WARN(1, "Attempt to destroy undead transport %p!\n", transport);
+ return;
+ }
+
+ sctp_packet_free(&transport->packet);
if (transport->asoc)
sctp_association_put(transport->asoc);
- sctp_packet_free(&transport->packet);
-
- dst_release(transport->dst);
- kfree(transport);
- SCTP_DBG_OBJCNT_DEC(transport);
+ call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
}
/* Start T3_rtx timer if it is not already running and update the heartbeat
@@ -223,45 +218,29 @@ void sctp_transport_set_owner(struct sctp_transport *transport,
}
/* Initialize the pmtu of a transport. */
-void sctp_transport_pmtu(struct sctp_transport *transport)
+void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
{
- struct dst_entry *dst;
-
- dst = transport->af_specific->get_dst(NULL, &transport->ipaddr, NULL);
+ /* If we don't have a fresh route, look one up */
+ if (!transport->dst || transport->dst->obsolete) {
+ dst_release(transport->dst);
+ transport->af_specific->get_dst(transport, &transport->saddr,
+ &transport->fl, sk);
+ }
- if (dst) {
- transport->pathmtu = dst_mtu(dst);
- dst_release(dst);
+ 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)
+void sctp_transport_update_pmtu(struct sock *sk, struct sctp_transport *t, u32 pmtu)
{
struct dst_entry *dst;
if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
- printk(KERN_WARNING "%s: Reported pmtu %d too low, "
- "using default minimum of %d\n",
- __FUNCTION__, pmtu,
- SCTP_DEFAULT_MINSEGMENT);
+ pr_warn("%s: Reported pmtu %d too low, using default minimum of %d\n",
+ __func__, pmtu,
+ SCTP_DEFAULT_MINSEGMENT);
/* Use default minimum segment size and disable
* pmtu discovery on this transport.
*/
@@ -271,8 +250,16 @@ void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
}
dst = sctp_transport_dst_check(t);
- if (dst)
- dst->ops->update_pmtu(dst, pmtu);
+ if (!dst)
+ t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
+
+ if (dst) {
+ dst->ops->update_pmtu(dst, sk, NULL, pmtu);
+
+ dst = sctp_transport_dst_check(t);
+ if (!dst)
+ t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
+ }
}
/* Caches the dst entry and source address for a transport's destination
@@ -283,27 +270,25 @@ void sctp_transport_route(struct sctp_transport *transport,
{
struct sctp_association *asoc = transport->asoc;
struct sctp_af *af = transport->af_specific;
- union sctp_addr *daddr = &transport->ipaddr;
- struct dst_entry *dst;
- dst = af->get_dst(asoc, daddr, saddr);
+ af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));
if (saddr)
memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
else
- af->get_saddr(asoc, dst, daddr, &transport->saddr);
+ af->get_saddr(opt, transport, &transport->fl);
- transport->dst = dst;
if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
return;
}
- if (dst) {
- transport->pathmtu = dst_mtu(dst);
+ 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 && (transport == asoc->peer.active_path))
+ if (asoc && (!asoc->peer.primary_path ||
+ (transport == asoc->peer.active_path)))
opt->pf->af->to_sk_saddr(&transport->saddr,
asoc->base.sk);
} else
@@ -328,13 +313,12 @@ void sctp_transport_put(struct sctp_transport *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 (unlikely(!tp->rto_pending))
+ /* We should not be doing any RTO updates unless rto_pending is set. */
+ pr_debug("%s: rto_pending not set on transport %p!\n", __func__, tp);
if (tp->rttvar || tp->srtt) {
+ struct net *net = sock_net(tp->asoc->base.sk);
/* 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'
@@ -346,10 +330,10 @@ void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
* 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);
+ tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
+ + (((__u32)abs64((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
+ tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
+ + (rtt >> net->sctp.rto_alpha);
} else {
/* 6.3.1 C2) When the first RTT measurement R is made, set
* SRTT <- R, RTTVAR <- R/2.
@@ -379,17 +363,16 @@ void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
if (tp->rto > tp->asoc->rto_max)
tp->rto = tp->asoc->rto_max;
+ sctp_max_rto(tp->asoc, tp);
tp->rtt = rtt;
- tp->last_rto = tp->rto;
/* 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\n", __FUNCTION__,
- tp, rtt, tp->srtt, tp->rttvar, tp->rto);
+ pr_debug("%s: transport:%p, rtt:%d, srtt:%d rttvar:%d, rto:%ld\n",
+ __func__, tp, rtt, tp->srtt, tp->rttvar, tp->rto);
}
/* This routine updates the transport's cwnd and partial_bytes_acked
@@ -398,16 +381,22 @@ void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
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 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;
@@ -416,27 +405,32 @@ 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 (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\n",
- __FUNCTION__,
- transport, bytes_acked, cwnd,
- ssthresh, flight_size, pba);
+
+ pr_debug("%s: slow start: transport:%p, bytes_acked:%d, "
+ "cwnd:%d, ssthresh:%d, flight_size:%d, pba:%d\n",
+ __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
@@ -457,12 +451,12 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport,
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\n",
- __FUNCTION__,
- transport, bytes_acked, cwnd,
- ssthresh, flight_size, pba);
+
+ pr_debug("%s: congestion avoidance: transport:%p, "
+ "bytes_acked:%d, cwnd:%d, ssthresh:%d, "
+ "flight_size:%d, pba:%d\n", __func__,
+ transport, bytes_acked, cwnd, ssthresh,
+ flight_size, pba);
}
transport->cwnd = cwnd;
@@ -475,6 +469,8 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport,
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
@@ -485,8 +481,11 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport,
* partial_bytes_acked = 0
*/
transport->ssthresh = max(transport->cwnd/2,
- 4*transport->asoc->pathmtu);
- transport->cwnd = transport->asoc->pathmtu;
+ 4*asoc->pathmtu);
+ transport->cwnd = asoc->pathmtu;
+
+ /* T3-rtx also clears fast recovery */
+ asoc->fast_recovery = 0;
break;
case SCTP_LOWER_CWND_FAST_RTX:
@@ -502,8 +501,15 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport,
* 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*transport->asoc->pathmtu);
+ 4*asoc->pathmtu);
transport->cwnd = transport->ssthresh;
break;
@@ -520,10 +526,10 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport,
* congestion indications more than once every window of
* data (or more loosely more than once every round-trip time).
*/
- if ((jiffies - transport->last_time_ecne_reduced) >
- transport->rtt) {
+ if (time_after(jiffies, transport->last_time_ecne_reduced +
+ transport->rtt)) {
transport->ssthresh = max(transport->cwnd/2,
- 4*transport->asoc->pathmtu);
+ 4*asoc->pathmtu);
transport->cwnd = transport->ssthresh;
transport->last_time_ecne_reduced = jiffies;
}
@@ -538,17 +544,53 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport,
* to be done every RTO interval, we do it every hearbeat
* interval.
*/
- if ((jiffies - transport->last_time_used) > transport->rto)
- transport->cwnd = max(transport->cwnd/2,
- 4*transport->asoc->pathmtu);
+ 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\n", __FUNCTION__,
- transport, reason,
- transport->cwnd, transport->ssthresh);
+
+ pr_debug("%s: transport:%p, reason:%d, cwnd:%d, ssthresh:%d\n",
+ __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 || asoc->max_burst == 0)
+ 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? */
@@ -556,7 +598,8 @@ unsigned long sctp_transport_timeout(struct sctp_transport *t)
{
unsigned long timeout;
timeout = t->rto + sctp_jitter(t->rto);
- if (t->state != SCTP_UNCONFIRMED)
+ if ((t->state != SCTP_UNCONFIRMED) &&
+ (t->state != SCTP_PF))
timeout += t->hbinterval;
timeout += jiffies;
return timeout;
@@ -573,8 +616,10 @@ void sctp_transport_reset(struct sctp_transport *t)
* (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->last_rto = t->rto = asoc->rto_initial;
+ t->rto = asoc->rto_initial;
+ sctp_max_rto(asoc, t);
t->rtt = 0;
t->srtt = 0;
t->rttvar = 0;
@@ -586,6 +631,7 @@ void sctp_transport_reset(struct sctp_transport *t)
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;
@@ -593,3 +639,17 @@ void sctp_transport_reset(struct sctp_transport *t)
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 (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);
+ }
+}