2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * Implementation of the Transmission Control Protocol(TCP).
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
21 #include <linux/module.h>
22 #include <linux/gfp.h>
25 int sysctl_tcp_syn_retries __read_mostly
= TCP_SYN_RETRIES
;
26 int sysctl_tcp_synack_retries __read_mostly
= TCP_SYNACK_RETRIES
;
27 int sysctl_tcp_keepalive_time __read_mostly
= TCP_KEEPALIVE_TIME
;
28 int sysctl_tcp_keepalive_probes __read_mostly
= TCP_KEEPALIVE_PROBES
;
29 int sysctl_tcp_keepalive_intvl __read_mostly
= TCP_KEEPALIVE_INTVL
;
30 int sysctl_tcp_retries1 __read_mostly
= TCP_RETR1
;
31 int sysctl_tcp_retries2 __read_mostly
= TCP_RETR2
;
32 int sysctl_tcp_orphan_retries __read_mostly
;
33 int sysctl_tcp_thin_linear_timeouts __read_mostly
;
34 int sysctl_tcp_rto_min __read_mostly
= TCP_RTO_MIN
;
35 EXPORT_SYMBOL(sysctl_tcp_rto_min
);
36 int sysctl_tcp_rto_max __read_mostly
= TCP_RTO_MAX
;
37 EXPORT_SYMBOL(sysctl_tcp_rto_max
);
39 static void tcp_write_err(struct sock
*sk
)
41 sk
->sk_err
= sk
->sk_err_soft
? : ETIMEDOUT
;
42 sk
->sk_error_report(sk
);
45 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPABORTONTIMEOUT
);
48 /* Do not allow orphaned sockets to eat all our resources.
49 * This is direct violation of TCP specs, but it is required
50 * to prevent DoS attacks. It is called when a retransmission timeout
51 * or zero probe timeout occurs on orphaned socket.
53 * Criteria is still not confirmed experimentally and may change.
54 * We kill the socket, if:
55 * 1. If number of orphaned sockets exceeds an administratively configured
57 * 2. If we have strong memory pressure.
59 static int tcp_out_of_resources(struct sock
*sk
, int do_reset
)
61 struct tcp_sock
*tp
= tcp_sk(sk
);
64 /* If peer does not open window for long time, or did not transmit
65 * anything for long time, penalize it. */
66 if ((s32
)(tcp_time_stamp
- tp
->lsndtime
) > 2*sysctl_tcp_rto_max
|| !do_reset
)
69 /* If some dubious ICMP arrived, penalize even more. */
73 if (tcp_check_oom(sk
, shift
)) {
74 /* Catch exceptional cases, when connection requires reset.
75 * 1. Last segment was sent recently. */
76 if ((s32
)(tcp_time_stamp
- tp
->lsndtime
) <= TCP_TIMEWAIT_LEN
||
77 /* 2. Window is closed. */
78 (!tp
->snd_wnd
&& !tp
->packets_out
))
81 tcp_send_active_reset(sk
, GFP_ATOMIC
);
83 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPABORTONMEMORY
);
89 /* Calculate maximal number or retries on an orphaned socket. */
90 static int tcp_orphan_retries(struct sock
*sk
, int alive
)
92 int retries
= sysctl_tcp_orphan_retries
; /* May be zero. */
94 /* We know from an ICMP that something is wrong. */
95 if (sk
->sk_err_soft
&& !alive
)
98 /* However, if socket sent something recently, select some safe
99 * number of retries. 8 corresponds to >100 seconds with minimal
101 if (retries
== 0 && alive
)
106 static void tcp_mtu_probing(struct inet_connection_sock
*icsk
, struct sock
*sk
)
108 /* Black hole detection */
109 if (sysctl_tcp_mtu_probing
) {
110 if (!icsk
->icsk_mtup
.enabled
) {
111 icsk
->icsk_mtup
.enabled
= 1;
112 tcp_sync_mss(sk
, icsk
->icsk_pmtu_cookie
);
114 struct tcp_sock
*tp
= tcp_sk(sk
);
117 mss
= tcp_mtu_to_mss(sk
, icsk
->icsk_mtup
.search_low
) >> 1;
118 mss
= min(sysctl_tcp_base_mss
, mss
);
119 mss
= max(mss
, 68 - tp
->tcp_header_len
);
120 icsk
->icsk_mtup
.search_low
= tcp_mss_to_mtu(sk
, mss
);
121 tcp_sync_mss(sk
, icsk
->icsk_pmtu_cookie
);
126 /* This function calculates a "timeout" which is equivalent to the timeout of a
127 * TCP connection after "boundary" unsuccessful, exponentially backed-off
128 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
129 * syn_set flag is set.
131 static bool retransmits_timed_out(struct sock
*sk
,
132 unsigned int boundary
,
133 unsigned int timeout
,
136 unsigned int linear_backoff_thresh
, start_ts
;
137 unsigned int rto_base
= syn_set
? TCP_TIMEOUT_INIT
: sysctl_tcp_rto_min
;
139 if (!inet_csk(sk
)->icsk_retransmits
)
142 if (unlikely(!tcp_sk(sk
)->retrans_stamp
))
143 start_ts
= TCP_SKB_CB(tcp_write_queue_head(sk
))->when
;
145 start_ts
= tcp_sk(sk
)->retrans_stamp
;
147 if (likely(timeout
== 0)) {
148 linear_backoff_thresh
= ilog2(sysctl_tcp_rto_max
/rto_base
);
150 if (boundary
<= linear_backoff_thresh
)
151 timeout
= ((2 << boundary
) - 1) * rto_base
;
153 timeout
= ((2 << linear_backoff_thresh
) - 1) * rto_base
+
154 (boundary
- linear_backoff_thresh
) * sysctl_tcp_rto_max
;
156 return (tcp_time_stamp
- start_ts
) >= timeout
;
159 /* A write timeout has occurred. Process the after effects. */
160 static int tcp_write_timeout(struct sock
*sk
)
162 struct inet_connection_sock
*icsk
= inet_csk(sk
);
164 bool do_reset
, syn_set
= false;
166 if ((1 << sk
->sk_state
) & (TCPF_SYN_SENT
| TCPF_SYN_RECV
)) {
167 if (icsk
->icsk_retransmits
)
168 dst_negative_advice(sk
);
169 retry_until
= icsk
->icsk_syn_retries
? : sysctl_tcp_syn_retries
;
172 if (retransmits_timed_out(sk
, sysctl_tcp_retries1
, 0, 0)) {
173 /* Black hole detection */
174 tcp_mtu_probing(icsk
, sk
);
176 dst_negative_advice(sk
);
179 retry_until
= sysctl_tcp_retries2
;
180 if (sock_flag(sk
, SOCK_DEAD
)) {
181 const int alive
= (icsk
->icsk_rto
< sysctl_tcp_rto_max
);
183 retry_until
= tcp_orphan_retries(sk
, alive
);
185 !retransmits_timed_out(sk
, retry_until
, 0, 0);
187 if (tcp_out_of_resources(sk
, do_reset
))
192 if (retransmits_timed_out(sk
, retry_until
,
193 syn_set
? 0 : icsk
->icsk_user_timeout
, syn_set
)) {
194 /* Has it gone just too far? */
201 void tcp_delack_timer_handler(struct sock
*sk
)
203 struct tcp_sock
*tp
= tcp_sk(sk
);
204 struct inet_connection_sock
*icsk
= inet_csk(sk
);
206 sk_mem_reclaim_partial(sk
);
208 if (sk
->sk_state
== TCP_CLOSE
|| !(icsk
->icsk_ack
.pending
& ICSK_ACK_TIMER
))
211 if (time_after(icsk
->icsk_ack
.timeout
, jiffies
)) {
212 sk_reset_timer(sk
, &icsk
->icsk_delack_timer
, icsk
->icsk_ack
.timeout
);
215 icsk
->icsk_ack
.pending
&= ~ICSK_ACK_TIMER
;
217 if (!skb_queue_empty(&tp
->ucopy
.prequeue
)) {
220 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPSCHEDULERFAILED
);
222 while ((skb
= __skb_dequeue(&tp
->ucopy
.prequeue
)) != NULL
)
223 sk_backlog_rcv(sk
, skb
);
225 tp
->ucopy
.memory
= 0;
228 if (inet_csk_ack_scheduled(sk
)) {
229 if (!icsk
->icsk_ack
.pingpong
) {
230 /* Delayed ACK missed: inflate ATO. */
231 icsk
->icsk_ack
.ato
= min(icsk
->icsk_ack
.ato
<< 1, icsk
->icsk_rto
);
233 /* Delayed ACK missed: leave pingpong mode and
236 icsk
->icsk_ack
.pingpong
= 0;
237 icsk
->icsk_ack
.ato
= TCP_ATO_MIN
;
240 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_DELAYEDACKS
);
244 if (sk_under_memory_pressure(sk
))
248 static void tcp_delack_timer(unsigned long data
)
250 struct sock
*sk
= (struct sock
*)data
;
253 if (!sock_owned_by_user(sk
)) {
254 tcp_delack_timer_handler(sk
);
256 inet_csk(sk
)->icsk_ack
.blocked
= 1;
257 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_DELAYEDACKLOCKED
);
258 /* deleguate our work to tcp_release_cb() */
259 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED
, &tcp_sk(sk
)->tsq_flags
))
266 static void tcp_probe_timer(struct sock
*sk
)
268 struct inet_connection_sock
*icsk
= inet_csk(sk
);
269 struct tcp_sock
*tp
= tcp_sk(sk
);
272 if (tp
->packets_out
|| !tcp_send_head(sk
)) {
273 icsk
->icsk_probes_out
= 0;
277 /* *WARNING* RFC 1122 forbids this
279 * It doesn't AFAIK, because we kill the retransmit timer -AK
281 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
282 * this behaviour in Solaris down as a bug fix. [AC]
284 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
285 * even if they advertise zero window. Hence, connection is killed only
286 * if we received no ACKs for normal connection timeout. It is not killed
287 * only because window stays zero for some time, window may be zero
288 * until armageddon and even later. We are in full accordance
289 * with RFCs, only probe timer combines both retransmission timeout
290 * and probe timeout in one bottle. --ANK
292 max_probes
= sysctl_tcp_retries2
;
294 if (sock_flag(sk
, SOCK_DEAD
)) {
295 const int alive
= ((icsk
->icsk_rto
<< icsk
->icsk_backoff
) < sysctl_tcp_rto_max
);
297 max_probes
= tcp_orphan_retries(sk
, alive
);
299 if (tcp_out_of_resources(sk
, alive
|| icsk
->icsk_probes_out
<= max_probes
))
303 if (icsk
->icsk_probes_out
> max_probes
) {
306 /* Only send another probe if we didn't close things up. */
312 * Timer for Fast Open socket to retransmit SYNACK. Note that the
313 * sk here is the child socket, not the parent (listener) socket.
315 static void tcp_fastopen_synack_timer(struct sock
*sk
)
317 struct inet_connection_sock
*icsk
= inet_csk(sk
);
318 int max_retries
= icsk
->icsk_syn_retries
? :
319 sysctl_tcp_synack_retries
+ 1; /* add one more retry for fastopen */
320 struct request_sock
*req
;
322 req
= tcp_sk(sk
)->fastopen_rsk
;
323 req
->rsk_ops
->syn_ack_timeout(sk
, req
);
325 if (req
->num_timeout
>= max_retries
) {
329 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
330 * returned from rtx_syn_ack() to make it more persistent like
331 * regular retransmit because if the child socket has been accepted
332 * it's not good to give up too easily.
334 inet_rtx_syn_ack(sk
, req
);
336 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
337 TCP_TIMEOUT_INIT
<< req
->num_timeout
, sysctl_tcp_rto_max
);
341 * The TCP retransmit timer.
344 void tcp_retransmit_timer(struct sock
*sk
)
346 struct tcp_sock
*tp
= tcp_sk(sk
);
347 struct inet_connection_sock
*icsk
= inet_csk(sk
);
349 if (tp
->fastopen_rsk
) {
350 WARN_ON_ONCE(sk
->sk_state
!= TCP_SYN_RECV
&&
351 sk
->sk_state
!= TCP_FIN_WAIT1
);
352 tcp_fastopen_synack_timer(sk
);
353 /* Before we receive ACK to our SYN-ACK don't retransmit
354 * anything else (e.g., data or FIN segments).
358 if (!tp
->packets_out
)
361 WARN_ON(tcp_write_queue_empty(sk
));
363 tp
->tlp_high_seq
= 0;
365 if (!tp
->snd_wnd
&& !sock_flag(sk
, SOCK_DEAD
) &&
366 !((1 << sk
->sk_state
) & (TCPF_SYN_SENT
| TCPF_SYN_RECV
))) {
367 /* Receiver dastardly shrinks window. Our retransmits
368 * become zero probes, but we should not timeout this
369 * connection. If the socket is an orphan, time it out,
370 * we cannot allow such beasts to hang infinitely.
372 struct inet_sock
*inet
= inet_sk(sk
);
373 if (sk
->sk_family
== AF_INET
) {
374 LIMIT_NETDEBUG(KERN_DEBUG
pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
376 ntohs(inet
->inet_dport
), inet
->inet_num
,
377 tp
->snd_una
, tp
->snd_nxt
);
379 #if IS_ENABLED(CONFIG_IPV6)
380 else if (sk
->sk_family
== AF_INET6
) {
381 struct ipv6_pinfo
*np
= inet6_sk(sk
);
382 LIMIT_NETDEBUG(KERN_DEBUG
pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
384 ntohs(inet
->inet_dport
), inet
->inet_num
,
385 tp
->snd_una
, tp
->snd_nxt
);
388 if (tcp_time_stamp
- tp
->rcv_tstamp
> sysctl_tcp_rto_max
) {
392 tcp_enter_loss(sk
, 0);
393 tcp_retransmit_skb(sk
, tcp_write_queue_head(sk
));
395 goto out_reset_timer
;
398 if (tcp_write_timeout(sk
))
401 if (icsk
->icsk_retransmits
== 0) {
404 if (icsk
->icsk_ca_state
== TCP_CA_Recovery
) {
406 mib_idx
= LINUX_MIB_TCPSACKRECOVERYFAIL
;
408 mib_idx
= LINUX_MIB_TCPRENORECOVERYFAIL
;
409 } else if (icsk
->icsk_ca_state
== TCP_CA_Loss
) {
410 mib_idx
= LINUX_MIB_TCPLOSSFAILURES
;
411 } else if ((icsk
->icsk_ca_state
== TCP_CA_Disorder
) ||
414 mib_idx
= LINUX_MIB_TCPSACKFAILURES
;
416 mib_idx
= LINUX_MIB_TCPRENOFAILURES
;
418 mib_idx
= LINUX_MIB_TCPTIMEOUTS
;
420 NET_INC_STATS_BH(sock_net(sk
), mib_idx
);
423 if (icsk
->icsk_MMSRB
== 1)
425 #ifdef CONFIG_MTK_NET_LOGGING
426 printk(KERN_DEBUG
"[mtk_net][mmspb] tcp_retransmit_timer enter loss\n");
429 tcp_enter_loss(sk
, 0);
431 if (tcp_retransmit_skb(sk
, tcp_write_queue_head(sk
)) > 0) {
432 /* Retransmission failed because of local congestion,
435 if (!icsk
->icsk_retransmits
)
436 icsk
->icsk_retransmits
= 1;
437 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
,
438 min(icsk
->icsk_rto
, TCP_RESOURCE_PROBE_INTERVAL
),
443 /* Increase the timeout each time we retransmit. Note that
444 * we do not increase the rtt estimate. rto is initialized
445 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
446 * that doubling rto each time is the least we can get away with.
447 * In KA9Q, Karn uses this for the first few times, and then
448 * goes to quadratic. netBSD doubles, but only goes up to *64,
449 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
450 * defined in the protocol as the maximum possible RTT. I guess
451 * we'll have to use something other than TCP to talk to the
452 * University of Mars.
454 * PAWS allows us longer timeouts and large windows, so once
455 * implemented ftp to mars will work nicely. We will have to fix
456 * the 120 second clamps though!
458 icsk
->icsk_backoff
++;
459 icsk
->icsk_retransmits
++;
462 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
463 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
464 * might be increased if the stream oscillates between thin and thick,
465 * thus the old value might already be too high compared to the value
466 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
467 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
468 * exponential backoff behaviour to avoid continue hammering
469 * linear-timeout retransmissions into a black hole
471 if (sk
->sk_state
== TCP_ESTABLISHED
&&
472 (tp
->thin_lto
|| sysctl_tcp_thin_linear_timeouts
) &&
473 tcp_stream_is_thin(tp
) &&
474 icsk
->icsk_retransmits
<= TCP_THIN_LINEAR_RETRIES
) {
475 icsk
->icsk_backoff
= 0;
476 icsk
->icsk_rto
= min_t(unsigned int, __tcp_set_rto(tp
), sysctl_tcp_rto_max
);
478 /* Use normal (exponential) backoff */
479 icsk
->icsk_rto
= min_t(unsigned int, icsk
->icsk_rto
<< 1, sysctl_tcp_rto_max
);
481 inet_csk_reset_xmit_timer(sk
, ICSK_TIME_RETRANS
, icsk
->icsk_rto
, sysctl_tcp_rto_max
);
482 if (retransmits_timed_out(sk
, sysctl_tcp_retries1
+ 1, 0, 0))
488 void tcp_write_timer_handler(struct sock
*sk
)
490 struct inet_connection_sock
*icsk
= inet_csk(sk
);
493 if (sk
->sk_state
== TCP_CLOSE
|| !icsk
->icsk_pending
)
495 if (icsk
->icsk_MMSRB
!= 1)
497 if (time_after(icsk
->icsk_timeout
, jiffies
)) {
498 sk_reset_timer(sk
, &icsk
->icsk_retransmit_timer
, icsk
->icsk_timeout
);
502 event
= icsk
->icsk_pending
;
505 case ICSK_TIME_EARLY_RETRANS
:
506 tcp_resume_early_retransmit(sk
);
508 case ICSK_TIME_LOSS_PROBE
:
509 tcp_send_loss_probe(sk
);
511 case ICSK_TIME_RETRANS
:
512 icsk
->icsk_pending
= 0;
513 tcp_retransmit_timer(sk
);
515 case ICSK_TIME_PROBE0
:
516 icsk
->icsk_pending
= 0;
525 static void tcp_write_timer(unsigned long data
)
527 struct sock
*sk
= (struct sock
*)data
;
530 if (!sock_owned_by_user(sk
)) {
531 tcp_write_timer_handler(sk
);
534 //if (icsk->icsk_MMSRB == 1)
535 //printk("[mmspb] tcp_write_timer user owner sock\n");
537 /* deleguate our work to tcp_release_cb() */
538 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED
, &tcp_sk(sk
)->tsq_flags
))
546 * Timer for listening sockets
549 static void tcp_synack_timer(struct sock
*sk
)
551 inet_csk_reqsk_queue_prune(sk
, TCP_SYNQ_INTERVAL
,
552 TCP_TIMEOUT_INIT
, sysctl_tcp_rto_max
);
555 void tcp_syn_ack_timeout(struct sock
*sk
, struct request_sock
*req
)
557 NET_INC_STATS_BH(sock_net(sk
), LINUX_MIB_TCPTIMEOUTS
);
559 EXPORT_SYMBOL(tcp_syn_ack_timeout
);
561 void tcp_set_keepalive(struct sock
*sk
, int val
)
563 if ((1 << sk
->sk_state
) & (TCPF_CLOSE
| TCPF_LISTEN
))
566 if (val
&& !sock_flag(sk
, SOCK_KEEPOPEN
))
567 inet_csk_reset_keepalive_timer(sk
, keepalive_time_when(tcp_sk(sk
)));
569 inet_csk_delete_keepalive_timer(sk
);
573 static void tcp_keepalive_timer (unsigned long data
)
575 struct sock
*sk
= (struct sock
*) data
;
576 struct inet_connection_sock
*icsk
= inet_csk(sk
);
577 struct tcp_sock
*tp
= tcp_sk(sk
);
580 /* Only process if socket is not in use. */
582 if (sock_owned_by_user(sk
)) {
583 /* Try again later. */
584 inet_csk_reset_keepalive_timer (sk
, HZ
/20);
588 if (sk
->sk_state
== TCP_LISTEN
) {
589 tcp_synack_timer(sk
);
593 if (sk
->sk_state
== TCP_FIN_WAIT2
&& sock_flag(sk
, SOCK_DEAD
)) {
594 if (tp
->linger2
>= 0) {
595 const int tmo
= tcp_fin_time(sk
) - TCP_TIMEWAIT_LEN
;
598 tcp_time_wait(sk
, TCP_FIN_WAIT2
, tmo
);
602 tcp_send_active_reset(sk
, GFP_ATOMIC
);
606 if (!sock_flag(sk
, SOCK_KEEPOPEN
) || sk
->sk_state
== TCP_CLOSE
)
609 elapsed
= keepalive_time_when(tp
);
611 /* It is alive without keepalive 8) */
612 if (tp
->packets_out
|| tcp_send_head(sk
))
615 elapsed
= keepalive_time_elapsed(tp
);
617 if (elapsed
>= keepalive_time_when(tp
)) {
618 /* If the TCP_USER_TIMEOUT option is enabled, use that
619 * to determine when to timeout instead.
621 if ((icsk
->icsk_user_timeout
!= 0 &&
622 elapsed
>= icsk
->icsk_user_timeout
&&
623 icsk
->icsk_probes_out
> 0) ||
624 (icsk
->icsk_user_timeout
== 0 &&
625 icsk
->icsk_probes_out
>= keepalive_probes(tp
))) {
626 tcp_send_active_reset(sk
, GFP_ATOMIC
);
630 if (tcp_write_wakeup(sk
) <= 0) {
631 icsk
->icsk_probes_out
++;
632 elapsed
= keepalive_intvl_when(tp
);
634 /* If keepalive was lost due to local congestion,
637 elapsed
= TCP_RESOURCE_PROBE_INTERVAL
;
640 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
641 elapsed
= keepalive_time_when(tp
) - elapsed
;
647 inet_csk_reset_keepalive_timer (sk
, elapsed
);
658 void tcp_init_xmit_timers(struct sock
*sk
)
660 inet_csk_init_xmit_timers(sk
, &tcp_write_timer
, &tcp_delack_timer
,
661 &tcp_keepalive_timer
);
663 EXPORT_SYMBOL(tcp_init_xmit_timers
);