tcp: refactor F-RTO
[linux-2.6-microblaze.git] / net / ipv4 / tcp_timer.c
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_err(struct sock *sk)
36 {
37         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
38         sk->sk_error_report(sk);
39
40         tcp_done(sk);
41         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
42 }
43
44 /* Do not allow orphaned sockets to eat all our resources.
45  * This is direct violation of TCP specs, but it is required
46  * to prevent DoS attacks. It is called when a retransmission timeout
47  * or zero probe timeout occurs on orphaned socket.
48  *
49  * Criteria is still not confirmed experimentally and may change.
50  * We kill the socket, if:
51  * 1. If number of orphaned sockets exceeds an administratively configured
52  *    limit.
53  * 2. If we have strong memory pressure.
54  */
55 static int tcp_out_of_resources(struct sock *sk, int do_reset)
56 {
57         struct tcp_sock *tp = tcp_sk(sk);
58         int shift = 0;
59
60         /* If peer does not open window for long time, or did not transmit
61          * anything for long time, penalize it. */
62         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
63                 shift++;
64
65         /* If some dubious ICMP arrived, penalize even more. */
66         if (sk->sk_err_soft)
67                 shift++;
68
69         if (tcp_check_oom(sk, shift)) {
70                 /* Catch exceptional cases, when connection requires reset.
71                  *      1. Last segment was sent recently. */
72                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
73                     /*  2. Window is closed. */
74                     (!tp->snd_wnd && !tp->packets_out))
75                         do_reset = 1;
76                 if (do_reset)
77                         tcp_send_active_reset(sk, GFP_ATOMIC);
78                 tcp_done(sk);
79                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
80                 return 1;
81         }
82         return 0;
83 }
84
85 /* Calculate maximal number or retries on an orphaned socket. */
86 static int tcp_orphan_retries(struct sock *sk, int alive)
87 {
88         int retries = sysctl_tcp_orphan_retries; /* May be zero. */
89
90         /* We know from an ICMP that something is wrong. */
91         if (sk->sk_err_soft && !alive)
92                 retries = 0;
93
94         /* However, if socket sent something recently, select some safe
95          * number of retries. 8 corresponds to >100 seconds with minimal
96          * RTO of 200msec. */
97         if (retries == 0 && alive)
98                 retries = 8;
99         return retries;
100 }
101
102 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
103 {
104         /* Black hole detection */
105         if (sysctl_tcp_mtu_probing) {
106                 if (!icsk->icsk_mtup.enabled) {
107                         icsk->icsk_mtup.enabled = 1;
108                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
109                 } else {
110                         struct tcp_sock *tp = tcp_sk(sk);
111                         int mss;
112
113                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
114                         mss = min(sysctl_tcp_base_mss, mss);
115                         mss = max(mss, 68 - tp->tcp_header_len);
116                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
117                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
118                 }
119         }
120 }
121
122 /* This function calculates a "timeout" which is equivalent to the timeout of a
123  * TCP connection after "boundary" unsuccessful, exponentially backed-off
124  * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
125  * syn_set flag is set.
126  */
127 static bool retransmits_timed_out(struct sock *sk,
128                                   unsigned int boundary,
129                                   unsigned int timeout,
130                                   bool syn_set)
131 {
132         unsigned int linear_backoff_thresh, start_ts;
133         unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
134
135         if (!inet_csk(sk)->icsk_retransmits)
136                 return false;
137
138         if (unlikely(!tcp_sk(sk)->retrans_stamp))
139                 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
140         else
141                 start_ts = tcp_sk(sk)->retrans_stamp;
142
143         if (likely(timeout == 0)) {
144                 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
145
146                 if (boundary <= linear_backoff_thresh)
147                         timeout = ((2 << boundary) - 1) * rto_base;
148                 else
149                         timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
150                                 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
151         }
152         return (tcp_time_stamp - start_ts) >= timeout;
153 }
154
155 /* A write timeout has occurred. Process the after effects. */
156 static int tcp_write_timeout(struct sock *sk)
157 {
158         struct inet_connection_sock *icsk = inet_csk(sk);
159         int retry_until;
160         bool do_reset, syn_set = false;
161
162         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
163                 if (icsk->icsk_retransmits)
164                         dst_negative_advice(sk);
165                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
166                 syn_set = true;
167         } else {
168                 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
169                         /* Black hole detection */
170                         tcp_mtu_probing(icsk, sk);
171
172                         dst_negative_advice(sk);
173                 }
174
175                 retry_until = sysctl_tcp_retries2;
176                 if (sock_flag(sk, SOCK_DEAD)) {
177                         const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
178
179                         retry_until = tcp_orphan_retries(sk, alive);
180                         do_reset = alive ||
181                                 !retransmits_timed_out(sk, retry_until, 0, 0);
182
183                         if (tcp_out_of_resources(sk, do_reset))
184                                 return 1;
185                 }
186         }
187
188         if (retransmits_timed_out(sk, retry_until,
189                                   syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
190                 /* Has it gone just too far? */
191                 tcp_write_err(sk);
192                 return 1;
193         }
194         return 0;
195 }
196
197 void tcp_delack_timer_handler(struct sock *sk)
198 {
199         struct tcp_sock *tp = tcp_sk(sk);
200         struct inet_connection_sock *icsk = inet_csk(sk);
201
202         sk_mem_reclaim_partial(sk);
203
204         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
205                 goto out;
206
207         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
208                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
209                 goto out;
210         }
211         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
212
213         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
214                 struct sk_buff *skb;
215
216                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
217
218                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
219                         sk_backlog_rcv(sk, skb);
220
221                 tp->ucopy.memory = 0;
222         }
223
224         if (inet_csk_ack_scheduled(sk)) {
225                 if (!icsk->icsk_ack.pingpong) {
226                         /* Delayed ACK missed: inflate ATO. */
227                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
228                 } else {
229                         /* Delayed ACK missed: leave pingpong mode and
230                          * deflate ATO.
231                          */
232                         icsk->icsk_ack.pingpong = 0;
233                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
234                 }
235                 tcp_send_ack(sk);
236                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
237         }
238
239 out:
240         if (sk_under_memory_pressure(sk))
241                 sk_mem_reclaim(sk);
242 }
243
244 static void tcp_delack_timer(unsigned long data)
245 {
246         struct sock *sk = (struct sock *)data;
247
248         bh_lock_sock(sk);
249         if (!sock_owned_by_user(sk)) {
250                 tcp_delack_timer_handler(sk);
251         } else {
252                 inet_csk(sk)->icsk_ack.blocked = 1;
253                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
254                 /* deleguate our work to tcp_release_cb() */
255                 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
256                         sock_hold(sk);
257         }
258         bh_unlock_sock(sk);
259         sock_put(sk);
260 }
261
262 static void tcp_probe_timer(struct sock *sk)
263 {
264         struct inet_connection_sock *icsk = inet_csk(sk);
265         struct tcp_sock *tp = tcp_sk(sk);
266         int max_probes;
267
268         if (tp->packets_out || !tcp_send_head(sk)) {
269                 icsk->icsk_probes_out = 0;
270                 return;
271         }
272
273         /* *WARNING* RFC 1122 forbids this
274          *
275          * It doesn't AFAIK, because we kill the retransmit timer -AK
276          *
277          * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
278          * this behaviour in Solaris down as a bug fix. [AC]
279          *
280          * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
281          * even if they advertise zero window. Hence, connection is killed only
282          * if we received no ACKs for normal connection timeout. It is not killed
283          * only because window stays zero for some time, window may be zero
284          * until armageddon and even later. We are in full accordance
285          * with RFCs, only probe timer combines both retransmission timeout
286          * and probe timeout in one bottle.                             --ANK
287          */
288         max_probes = sysctl_tcp_retries2;
289
290         if (sock_flag(sk, SOCK_DEAD)) {
291                 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
292
293                 max_probes = tcp_orphan_retries(sk, alive);
294
295                 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
296                         return;
297         }
298
299         if (icsk->icsk_probes_out > max_probes) {
300                 tcp_write_err(sk);
301         } else {
302                 /* Only send another probe if we didn't close things up. */
303                 tcp_send_probe0(sk);
304         }
305 }
306
307 /*
308  *      Timer for Fast Open socket to retransmit SYNACK. Note that the
309  *      sk here is the child socket, not the parent (listener) socket.
310  */
311 static void tcp_fastopen_synack_timer(struct sock *sk)
312 {
313         struct inet_connection_sock *icsk = inet_csk(sk);
314         int max_retries = icsk->icsk_syn_retries ? :
315             sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
316         struct request_sock *req;
317
318         req = tcp_sk(sk)->fastopen_rsk;
319         req->rsk_ops->syn_ack_timeout(sk, req);
320
321         if (req->num_timeout >= max_retries) {
322                 tcp_write_err(sk);
323                 return;
324         }
325         /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
326          * returned from rtx_syn_ack() to make it more persistent like
327          * regular retransmit because if the child socket has been accepted
328          * it's not good to give up too easily.
329          */
330         inet_rtx_syn_ack(sk, req);
331         req->num_timeout++;
332         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
333                           TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
334 }
335
336 /*
337  *      The TCP retransmit timer.
338  */
339
340 void tcp_retransmit_timer(struct sock *sk)
341 {
342         struct tcp_sock *tp = tcp_sk(sk);
343         struct inet_connection_sock *icsk = inet_csk(sk);
344
345         if (tp->fastopen_rsk) {
346                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
347                              sk->sk_state != TCP_FIN_WAIT1);
348                 tcp_fastopen_synack_timer(sk);
349                 /* Before we receive ACK to our SYN-ACK don't retransmit
350                  * anything else (e.g., data or FIN segments).
351                  */
352                 return;
353         }
354         if (!tp->packets_out)
355                 goto out;
356
357         WARN_ON(tcp_write_queue_empty(sk));
358
359         tp->tlp_high_seq = 0;
360
361         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
362             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
363                 /* Receiver dastardly shrinks window. Our retransmits
364                  * become zero probes, but we should not timeout this
365                  * connection. If the socket is an orphan, time it out,
366                  * we cannot allow such beasts to hang infinitely.
367                  */
368                 struct inet_sock *inet = inet_sk(sk);
369                 if (sk->sk_family == AF_INET) {
370                         LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
371                                        &inet->inet_daddr,
372                                        ntohs(inet->inet_dport), inet->inet_num,
373                                        tp->snd_una, tp->snd_nxt);
374                 }
375 #if IS_ENABLED(CONFIG_IPV6)
376                 else if (sk->sk_family == AF_INET6) {
377                         struct ipv6_pinfo *np = inet6_sk(sk);
378                         LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
379                                        &np->daddr,
380                                        ntohs(inet->inet_dport), inet->inet_num,
381                                        tp->snd_una, tp->snd_nxt);
382                 }
383 #endif
384                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
385                         tcp_write_err(sk);
386                         goto out;
387                 }
388                 tcp_enter_loss(sk, 0);
389                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
390                 __sk_dst_reset(sk);
391                 goto out_reset_timer;
392         }
393
394         if (tcp_write_timeout(sk))
395                 goto out;
396
397         if (icsk->icsk_retransmits == 0) {
398                 int mib_idx;
399
400                 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
401                         if (tcp_is_sack(tp))
402                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
403                         else
404                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
405                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
406                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
407                 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
408                            tp->sacked_out) {
409                         if (tcp_is_sack(tp))
410                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
411                         else
412                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
413                 } else {
414                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
415                 }
416                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
417         }
418
419         tcp_enter_loss(sk, 0);
420
421         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
422                 /* Retransmission failed because of local congestion,
423                  * do not backoff.
424                  */
425                 if (!icsk->icsk_retransmits)
426                         icsk->icsk_retransmits = 1;
427                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
428                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
429                                           TCP_RTO_MAX);
430                 goto out;
431         }
432
433         /* Increase the timeout each time we retransmit.  Note that
434          * we do not increase the rtt estimate.  rto is initialized
435          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
436          * that doubling rto each time is the least we can get away with.
437          * In KA9Q, Karn uses this for the first few times, and then
438          * goes to quadratic.  netBSD doubles, but only goes up to *64,
439          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
440          * defined in the protocol as the maximum possible RTT.  I guess
441          * we'll have to use something other than TCP to talk to the
442          * University of Mars.
443          *
444          * PAWS allows us longer timeouts and large windows, so once
445          * implemented ftp to mars will work nicely. We will have to fix
446          * the 120 second clamps though!
447          */
448         icsk->icsk_backoff++;
449         icsk->icsk_retransmits++;
450
451 out_reset_timer:
452         /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
453          * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
454          * might be increased if the stream oscillates between thin and thick,
455          * thus the old value might already be too high compared to the value
456          * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
457          * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
458          * exponential backoff behaviour to avoid continue hammering
459          * linear-timeout retransmissions into a black hole
460          */
461         if (sk->sk_state == TCP_ESTABLISHED &&
462             (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
463             tcp_stream_is_thin(tp) &&
464             icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
465                 icsk->icsk_backoff = 0;
466                 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
467         } else {
468                 /* Use normal (exponential) backoff */
469                 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
470         }
471         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
472         if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
473                 __sk_dst_reset(sk);
474
475 out:;
476 }
477
478 void tcp_write_timer_handler(struct sock *sk)
479 {
480         struct inet_connection_sock *icsk = inet_csk(sk);
481         int event;
482
483         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
484                 goto out;
485
486         if (time_after(icsk->icsk_timeout, jiffies)) {
487                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
488                 goto out;
489         }
490
491         event = icsk->icsk_pending;
492
493         switch (event) {
494         case ICSK_TIME_EARLY_RETRANS:
495                 tcp_resume_early_retransmit(sk);
496                 break;
497         case ICSK_TIME_LOSS_PROBE:
498                 tcp_send_loss_probe(sk);
499                 break;
500         case ICSK_TIME_RETRANS:
501                 icsk->icsk_pending = 0;
502                 tcp_retransmit_timer(sk);
503                 break;
504         case ICSK_TIME_PROBE0:
505                 icsk->icsk_pending = 0;
506                 tcp_probe_timer(sk);
507                 break;
508         }
509
510 out:
511         sk_mem_reclaim(sk);
512 }
513
514 static void tcp_write_timer(unsigned long data)
515 {
516         struct sock *sk = (struct sock *)data;
517
518         bh_lock_sock(sk);
519         if (!sock_owned_by_user(sk)) {
520                 tcp_write_timer_handler(sk);
521         } else {
522                 /* deleguate our work to tcp_release_cb() */
523                 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
524                         sock_hold(sk);
525         }
526         bh_unlock_sock(sk);
527         sock_put(sk);
528 }
529
530 /*
531  *      Timer for listening sockets
532  */
533
534 static void tcp_synack_timer(struct sock *sk)
535 {
536         inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
537                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
538 }
539
540 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
541 {
542         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
543 }
544 EXPORT_SYMBOL(tcp_syn_ack_timeout);
545
546 void tcp_set_keepalive(struct sock *sk, int val)
547 {
548         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
549                 return;
550
551         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
552                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
553         else if (!val)
554                 inet_csk_delete_keepalive_timer(sk);
555 }
556
557
558 static void tcp_keepalive_timer (unsigned long data)
559 {
560         struct sock *sk = (struct sock *) data;
561         struct inet_connection_sock *icsk = inet_csk(sk);
562         struct tcp_sock *tp = tcp_sk(sk);
563         u32 elapsed;
564
565         /* Only process if socket is not in use. */
566         bh_lock_sock(sk);
567         if (sock_owned_by_user(sk)) {
568                 /* Try again later. */
569                 inet_csk_reset_keepalive_timer (sk, HZ/20);
570                 goto out;
571         }
572
573         if (sk->sk_state == TCP_LISTEN) {
574                 tcp_synack_timer(sk);
575                 goto out;
576         }
577
578         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
579                 if (tp->linger2 >= 0) {
580                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
581
582                         if (tmo > 0) {
583                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
584                                 goto out;
585                         }
586                 }
587                 tcp_send_active_reset(sk, GFP_ATOMIC);
588                 goto death;
589         }
590
591         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
592                 goto out;
593
594         elapsed = keepalive_time_when(tp);
595
596         /* It is alive without keepalive 8) */
597         if (tp->packets_out || tcp_send_head(sk))
598                 goto resched;
599
600         elapsed = keepalive_time_elapsed(tp);
601
602         if (elapsed >= keepalive_time_when(tp)) {
603                 /* If the TCP_USER_TIMEOUT option is enabled, use that
604                  * to determine when to timeout instead.
605                  */
606                 if ((icsk->icsk_user_timeout != 0 &&
607                     elapsed >= icsk->icsk_user_timeout &&
608                     icsk->icsk_probes_out > 0) ||
609                     (icsk->icsk_user_timeout == 0 &&
610                     icsk->icsk_probes_out >= keepalive_probes(tp))) {
611                         tcp_send_active_reset(sk, GFP_ATOMIC);
612                         tcp_write_err(sk);
613                         goto out;
614                 }
615                 if (tcp_write_wakeup(sk) <= 0) {
616                         icsk->icsk_probes_out++;
617                         elapsed = keepalive_intvl_when(tp);
618                 } else {
619                         /* If keepalive was lost due to local congestion,
620                          * try harder.
621                          */
622                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
623                 }
624         } else {
625                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
626                 elapsed = keepalive_time_when(tp) - elapsed;
627         }
628
629         sk_mem_reclaim(sk);
630
631 resched:
632         inet_csk_reset_keepalive_timer (sk, elapsed);
633         goto out;
634
635 death:
636         tcp_done(sk);
637
638 out:
639         bh_unlock_sock(sk);
640         sock_put(sk);
641 }
642
643 void tcp_init_xmit_timers(struct sock *sk)
644 {
645         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
646                                   &tcp_keepalive_timer);
647 }
648 EXPORT_SYMBOL(tcp_init_xmit_timers);