1 /*
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.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
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>
19 */
20
21 #include <linux/module.h>
22 #include <linux/gfp.h>
23 #include <net/tcp.h>
24
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
35 static void tcp_write_timer(unsigned long);
36 static void tcp_delack_timer(unsigned long);
37 static void tcp_keepalive_timer (unsigned long data);
38
tcp_init_xmit_timers(struct sock * sk)39 void tcp_init_xmit_timers(struct sock *sk)
40 {
41 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
42 &tcp_keepalive_timer);
43 }
44 EXPORT_SYMBOL(tcp_init_xmit_timers);
45
tcp_write_err(struct sock * sk)46 static void tcp_write_err(struct sock *sk)
47 {
48 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
49 sk->sk_error_report(sk);
50
51 tcp_done(sk);
52 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
53 }
54
55 /* Do not allow orphaned sockets to eat all our resources.
56 * This is direct violation of TCP specs, but it is required
57 * to prevent DoS attacks. It is called when a retransmission timeout
58 * or zero probe timeout occurs on orphaned socket.
59 *
60 * Criteria is still not confirmed experimentally and may change.
61 * We kill the socket, if:
62 * 1. If number of orphaned sockets exceeds an administratively configured
63 * limit.
64 * 2. If we have strong memory pressure.
65 */
tcp_out_of_resources(struct sock * sk,int do_reset)66 static int tcp_out_of_resources(struct sock *sk, int do_reset)
67 {
68 struct tcp_sock *tp = tcp_sk(sk);
69 int shift = 0;
70
71 /* If peer does not open window for long time, or did not transmit
72 * anything for long time, penalize it. */
73 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
74 shift++;
75
76 /* If some dubious ICMP arrived, penalize even more. */
77 if (sk->sk_err_soft)
78 shift++;
79
80 if (tcp_check_oom(sk, shift)) {
81 /* Catch exceptional cases, when connection requires reset.
82 * 1. Last segment was sent recently. */
83 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
84 /* 2. Window is closed. */
85 (!tp->snd_wnd && !tp->packets_out))
86 do_reset = 1;
87 if (do_reset)
88 tcp_send_active_reset(sk, GFP_ATOMIC);
89 tcp_done(sk);
90 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
91 return 1;
92 }
93 return 0;
94 }
95
96 /* Calculate maximal number or retries on an orphaned socket. */
tcp_orphan_retries(struct sock * sk,int alive)97 static int tcp_orphan_retries(struct sock *sk, int alive)
98 {
99 int retries = sysctl_tcp_orphan_retries; /* May be zero. */
100
101 /* We know from an ICMP that something is wrong. */
102 if (sk->sk_err_soft && !alive)
103 retries = 0;
104
105 /* However, if socket sent something recently, select some safe
106 * number of retries. 8 corresponds to >100 seconds with minimal
107 * RTO of 200msec. */
108 if (retries == 0 && alive)
109 retries = 8;
110 return retries;
111 }
112
tcp_mtu_probing(struct inet_connection_sock * icsk,struct sock * sk)113 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
114 {
115 /* Black hole detection */
116 if (sysctl_tcp_mtu_probing) {
117 if (!icsk->icsk_mtup.enabled) {
118 icsk->icsk_mtup.enabled = 1;
119 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
120 } else {
121 struct tcp_sock *tp = tcp_sk(sk);
122 int mss;
123
124 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
125 mss = min(sysctl_tcp_base_mss, mss);
126 mss = max(mss, 68 - tp->tcp_header_len);
127 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
128 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
129 }
130 }
131 }
132
133 /* This function calculates a "timeout" which is equivalent to the timeout of a
134 * TCP connection after "boundary" unsuccessful, exponentially backed-off
135 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
136 * syn_set flag is set.
137 */
retransmits_timed_out(struct sock * sk,unsigned int boundary,unsigned int timeout,bool syn_set)138 static bool retransmits_timed_out(struct sock *sk,
139 unsigned int boundary,
140 unsigned int timeout,
141 bool syn_set)
142 {
143 unsigned int linear_backoff_thresh, start_ts;
144 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
145
146 if (!inet_csk(sk)->icsk_retransmits)
147 return false;
148
149 if (unlikely(!tcp_sk(sk)->retrans_stamp))
150 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
151 else
152 start_ts = tcp_sk(sk)->retrans_stamp;
153
154 if (likely(timeout == 0)) {
155 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
156
157 if (boundary <= linear_backoff_thresh)
158 timeout = ((2 << boundary) - 1) * rto_base;
159 else
160 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
161 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
162 }
163 return (tcp_time_stamp - start_ts) >= timeout;
164 }
165
166 /* A write timeout has occurred. Process the after effects. */
tcp_write_timeout(struct sock * sk)167 static int tcp_write_timeout(struct sock *sk)
168 {
169 struct inet_connection_sock *icsk = inet_csk(sk);
170 int retry_until;
171 bool do_reset, syn_set = false;
172
173 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
174 if (icsk->icsk_retransmits)
175 dst_negative_advice(sk);
176 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
177 syn_set = true;
178 } else {
179 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
180 /* Black hole detection */
181 tcp_mtu_probing(icsk, sk);
182
183 dst_negative_advice(sk);
184 }
185
186 retry_until = sysctl_tcp_retries2;
187 if (sock_flag(sk, SOCK_DEAD)) {
188 const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
189
190 retry_until = tcp_orphan_retries(sk, alive);
191 do_reset = alive ||
192 !retransmits_timed_out(sk, retry_until, 0, 0);
193
194 if (tcp_out_of_resources(sk, do_reset))
195 return 1;
196 }
197 }
198
199 if (retransmits_timed_out(sk, retry_until,
200 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
201 /* Has it gone just too far? */
202 tcp_write_err(sk);
203 return 1;
204 }
205 return 0;
206 }
207
tcp_delack_timer(unsigned long data)208 static void tcp_delack_timer(unsigned long data)
209 {
210 struct sock *sk = (struct sock *)data;
211 struct tcp_sock *tp = tcp_sk(sk);
212 struct inet_connection_sock *icsk = inet_csk(sk);
213
214 bh_lock_sock(sk);
215 if (sock_owned_by_user(sk)) {
216 /* Try again later. */
217 icsk->icsk_ack.blocked = 1;
218 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
219 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
220 goto out_unlock;
221 }
222
223 sk_mem_reclaim_partial(sk);
224
225 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
226 goto out;
227
228 if (time_after(icsk->icsk_ack.timeout, jiffies)) {
229 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
230 goto out;
231 }
232 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
233
234 if (!skb_queue_empty(&tp->ucopy.prequeue)) {
235 struct sk_buff *skb;
236
237 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
238
239 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
240 sk_backlog_rcv(sk, skb);
241
242 tp->ucopy.memory = 0;
243 }
244
245 if (inet_csk_ack_scheduled(sk)) {
246 if (!icsk->icsk_ack.pingpong) {
247 /* Delayed ACK missed: inflate ATO. */
248 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
249 } else {
250 /* Delayed ACK missed: leave pingpong mode and
251 * deflate ATO.
252 */
253 icsk->icsk_ack.pingpong = 0;
254 icsk->icsk_ack.ato = TCP_ATO_MIN;
255 }
256 tcp_send_ack(sk);
257 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
258 }
259
260 out:
261 if (sk_under_memory_pressure(sk))
262 sk_mem_reclaim(sk);
263 out_unlock:
264 bh_unlock_sock(sk);
265 sock_put(sk);
266 }
267
tcp_probe_timer(struct sock * sk)268 static void tcp_probe_timer(struct sock *sk)
269 {
270 struct inet_connection_sock *icsk = inet_csk(sk);
271 struct tcp_sock *tp = tcp_sk(sk);
272 int max_probes;
273
274 if (tp->packets_out || !tcp_send_head(sk)) {
275 icsk->icsk_probes_out = 0;
276 return;
277 }
278
279 /* *WARNING* RFC 1122 forbids this
280 *
281 * It doesn't AFAIK, because we kill the retransmit timer -AK
282 *
283 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
284 * this behaviour in Solaris down as a bug fix. [AC]
285 *
286 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
287 * even if they advertise zero window. Hence, connection is killed only
288 * if we received no ACKs for normal connection timeout. It is not killed
289 * only because window stays zero for some time, window may be zero
290 * until armageddon and even later. We are in full accordance
291 * with RFCs, only probe timer combines both retransmission timeout
292 * and probe timeout in one bottle. --ANK
293 */
294 max_probes = sysctl_tcp_retries2;
295
296 if (sock_flag(sk, SOCK_DEAD)) {
297 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
298
299 max_probes = tcp_orphan_retries(sk, alive);
300
301 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
302 return;
303 }
304
305 if (icsk->icsk_probes_out > max_probes) {
306 tcp_write_err(sk);
307 } else {
308 /* Only send another probe if we didn't close things up. */
309 tcp_send_probe0(sk);
310 }
311 }
312
313 /*
314 * The TCP retransmit timer.
315 */
316
tcp_retransmit_timer(struct sock * sk)317 void tcp_retransmit_timer(struct sock *sk)
318 {
319 struct tcp_sock *tp = tcp_sk(sk);
320 struct inet_connection_sock *icsk = inet_csk(sk);
321
322 if (!tp->packets_out)
323 goto out;
324
325 WARN_ON(tcp_write_queue_empty(sk));
326
327 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
328 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
329 /* Receiver dastardly shrinks window. Our retransmits
330 * become zero probes, but we should not timeout this
331 * connection. If the socket is an orphan, time it out,
332 * we cannot allow such beasts to hang infinitely.
333 */
334 struct inet_sock *inet = inet_sk(sk);
335 if (sk->sk_family == AF_INET) {
336 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
337 &inet->inet_daddr,
338 ntohs(inet->inet_dport), inet->inet_num,
339 tp->snd_una, tp->snd_nxt);
340 }
341 #if IS_ENABLED(CONFIG_IPV6)
342 else if (sk->sk_family == AF_INET6) {
343 struct ipv6_pinfo *np = inet6_sk(sk);
344 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
345 &np->daddr,
346 ntohs(inet->inet_dport), inet->inet_num,
347 tp->snd_una, tp->snd_nxt);
348 }
349 #endif
350 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
351 tcp_write_err(sk);
352 goto out;
353 }
354 tcp_enter_loss(sk, 0);
355 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
356 __sk_dst_reset(sk);
357 goto out_reset_timer;
358 }
359
360 if (tcp_write_timeout(sk))
361 goto out;
362
363 if (icsk->icsk_retransmits == 0) {
364 int mib_idx;
365
366 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
367 if (tcp_is_sack(tp))
368 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
369 else
370 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
371 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
372 mib_idx = LINUX_MIB_TCPLOSSFAILURES;
373 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
374 tp->sacked_out) {
375 if (tcp_is_sack(tp))
376 mib_idx = LINUX_MIB_TCPSACKFAILURES;
377 else
378 mib_idx = LINUX_MIB_TCPRENOFAILURES;
379 } else {
380 mib_idx = LINUX_MIB_TCPTIMEOUTS;
381 }
382 NET_INC_STATS_BH(sock_net(sk), mib_idx);
383 }
384
385 if (tcp_use_frto(sk)) {
386 tcp_enter_frto(sk);
387 } else {
388 tcp_enter_loss(sk, 0);
389 }
390
391 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
392 /* Retransmission failed because of local congestion,
393 * do not backoff.
394 */
395 if (!icsk->icsk_retransmits)
396 icsk->icsk_retransmits = 1;
397 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
398 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
399 TCP_RTO_MAX);
400 goto out;
401 }
402
403 /* Increase the timeout each time we retransmit. Note that
404 * we do not increase the rtt estimate. rto is initialized
405 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests
406 * that doubling rto each time is the least we can get away with.
407 * In KA9Q, Karn uses this for the first few times, and then
408 * goes to quadratic. netBSD doubles, but only goes up to *64,
409 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is
410 * defined in the protocol as the maximum possible RTT. I guess
411 * we'll have to use something other than TCP to talk to the
412 * University of Mars.
413 *
414 * PAWS allows us longer timeouts and large windows, so once
415 * implemented ftp to mars will work nicely. We will have to fix
416 * the 120 second clamps though!
417 */
418 icsk->icsk_backoff++;
419 icsk->icsk_retransmits++;
420
421 out_reset_timer:
422 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
423 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
424 * might be increased if the stream oscillates between thin and thick,
425 * thus the old value might already be too high compared to the value
426 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
427 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
428 * exponential backoff behaviour to avoid continue hammering
429 * linear-timeout retransmissions into a black hole
430 */
431 if (sk->sk_state == TCP_ESTABLISHED &&
432 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
433 tcp_stream_is_thin(tp) &&
434 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
435 icsk->icsk_backoff = 0;
436 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
437 } else {
438 /* Use normal (exponential) backoff */
439 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
440 }
441 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
442 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
443 __sk_dst_reset(sk);
444
445 out:;
446 }
447
tcp_write_timer(unsigned long data)448 static void tcp_write_timer(unsigned long data)
449 {
450 struct sock *sk = (struct sock *)data;
451 struct inet_connection_sock *icsk = inet_csk(sk);
452 int event;
453
454 bh_lock_sock(sk);
455 if (sock_owned_by_user(sk)) {
456 /* Try again later */
457 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
458 goto out_unlock;
459 }
460
461 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
462 goto out;
463
464 if (time_after(icsk->icsk_timeout, jiffies)) {
465 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
466 goto out;
467 }
468
469 event = icsk->icsk_pending;
470 icsk->icsk_pending = 0;
471
472 switch (event) {
473 case ICSK_TIME_RETRANS:
474 tcp_retransmit_timer(sk);
475 break;
476 case ICSK_TIME_PROBE0:
477 tcp_probe_timer(sk);
478 break;
479 }
480
481 out:
482 sk_mem_reclaim(sk);
483 out_unlock:
484 bh_unlock_sock(sk);
485 sock_put(sk);
486 }
487
488 /*
489 * Timer for listening sockets
490 */
491
tcp_synack_timer(struct sock * sk)492 static void tcp_synack_timer(struct sock *sk)
493 {
494 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
495 TCP_TIMEOUT_INIT, TCP_RTO_MAX);
496 }
497
tcp_syn_ack_timeout(struct sock * sk,struct request_sock * req)498 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
499 {
500 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
501 }
502 EXPORT_SYMBOL(tcp_syn_ack_timeout);
503
tcp_set_keepalive(struct sock * sk,int val)504 void tcp_set_keepalive(struct sock *sk, int val)
505 {
506 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
507 return;
508
509 if (val && !sock_flag(sk, SOCK_KEEPOPEN))
510 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
511 else if (!val)
512 inet_csk_delete_keepalive_timer(sk);
513 }
514
515
tcp_keepalive_timer(unsigned long data)516 static void tcp_keepalive_timer (unsigned long data)
517 {
518 struct sock *sk = (struct sock *) data;
519 struct inet_connection_sock *icsk = inet_csk(sk);
520 struct tcp_sock *tp = tcp_sk(sk);
521 u32 elapsed;
522
523 /* Only process if socket is not in use. */
524 bh_lock_sock(sk);
525 if (sock_owned_by_user(sk)) {
526 /* Try again later. */
527 inet_csk_reset_keepalive_timer (sk, HZ/20);
528 goto out;
529 }
530
531 if (sk->sk_state == TCP_LISTEN) {
532 tcp_synack_timer(sk);
533 goto out;
534 }
535
536 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
537 if (tp->linger2 >= 0) {
538 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
539
540 if (tmo > 0) {
541 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
542 goto out;
543 }
544 }
545 tcp_send_active_reset(sk, GFP_ATOMIC);
546 goto death;
547 }
548
549 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
550 goto out;
551
552 elapsed = keepalive_time_when(tp);
553
554 /* It is alive without keepalive 8) */
555 if (tp->packets_out || tcp_send_head(sk))
556 goto resched;
557
558 elapsed = keepalive_time_elapsed(tp);
559
560 if (elapsed >= keepalive_time_when(tp)) {
561 /* If the TCP_USER_TIMEOUT option is enabled, use that
562 * to determine when to timeout instead.
563 */
564 if ((icsk->icsk_user_timeout != 0 &&
565 elapsed >= icsk->icsk_user_timeout &&
566 icsk->icsk_probes_out > 0) ||
567 (icsk->icsk_user_timeout == 0 &&
568 icsk->icsk_probes_out >= keepalive_probes(tp))) {
569 tcp_send_active_reset(sk, GFP_ATOMIC);
570 tcp_write_err(sk);
571 goto out;
572 }
573 if (tcp_write_wakeup(sk) <= 0) {
574 icsk->icsk_probes_out++;
575 elapsed = keepalive_intvl_when(tp);
576 } else {
577 /* If keepalive was lost due to local congestion,
578 * try harder.
579 */
580 elapsed = TCP_RESOURCE_PROBE_INTERVAL;
581 }
582 } else {
583 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
584 elapsed = keepalive_time_when(tp) - elapsed;
585 }
586
587 sk_mem_reclaim(sk);
588
589 resched:
590 inet_csk_reset_keepalive_timer (sk, elapsed);
591 goto out;
592
593 death:
594 tcp_done(sk);
595
596 out:
597 bh_unlock_sock(sk);
598 sock_put(sk);
599 }
600