xref: /openbmc/linux/net/ipv4/tcp_timer.c (revision bbecb07f)
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 /**
26  *  tcp_write_err() - close socket and save error info
27  *  @sk:  The socket the error has appeared on.
28  *
29  *  Returns: Nothing (void)
30  */
31 
32 static void tcp_write_err(struct sock *sk)
33 {
34 	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
35 	sk->sk_error_report(sk);
36 
37 	tcp_done(sk);
38 	__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
39 }
40 
41 /**
42  *  tcp_out_of_resources() - Close socket if out of resources
43  *  @sk:        pointer to current socket
44  *  @do_reset:  send a last packet with reset flag
45  *
46  *  Do not allow orphaned sockets to eat all our resources.
47  *  This is direct violation of TCP specs, but it is required
48  *  to prevent DoS attacks. It is called when a retransmission timeout
49  *  or zero probe timeout occurs on orphaned socket.
50  *
51  *  Criteria is still not confirmed experimentally and may change.
52  *  We kill the socket, if:
53  *  1. If number of orphaned sockets exceeds an administratively configured
54  *     limit.
55  *  2. If we have strong memory pressure.
56  */
57 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
58 {
59 	struct tcp_sock *tp = tcp_sk(sk);
60 	int shift = 0;
61 
62 	/* If peer does not open window for long time, or did not transmit
63 	 * anything for long time, penalize it. */
64 	if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
65 		shift++;
66 
67 	/* If some dubious ICMP arrived, penalize even more. */
68 	if (sk->sk_err_soft)
69 		shift++;
70 
71 	if (tcp_check_oom(sk, shift)) {
72 		/* Catch exceptional cases, when connection requires reset.
73 		 *      1. Last segment was sent recently. */
74 		if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
75 		    /*  2. Window is closed. */
76 		    (!tp->snd_wnd && !tp->packets_out))
77 			do_reset = true;
78 		if (do_reset)
79 			tcp_send_active_reset(sk, GFP_ATOMIC);
80 		tcp_done(sk);
81 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
82 		return 1;
83 	}
84 	return 0;
85 }
86 
87 /**
88  *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
89  *  @sk:    Pointer to the current socket.
90  *  @alive: bool, socket alive state
91  */
92 static int tcp_orphan_retries(struct sock *sk, bool alive)
93 {
94 	int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */
95 
96 	/* We know from an ICMP that something is wrong. */
97 	if (sk->sk_err_soft && !alive)
98 		retries = 0;
99 
100 	/* However, if socket sent something recently, select some safe
101 	 * number of retries. 8 corresponds to >100 seconds with minimal
102 	 * RTO of 200msec. */
103 	if (retries == 0 && alive)
104 		retries = 8;
105 	return retries;
106 }
107 
108 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
109 {
110 	const struct net *net = sock_net(sk);
111 	int mss;
112 
113 	/* Black hole detection */
114 	if (!net->ipv4.sysctl_tcp_mtu_probing)
115 		return;
116 
117 	if (!icsk->icsk_mtup.enabled) {
118 		icsk->icsk_mtup.enabled = 1;
119 		icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
120 	} else {
121 		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
122 		mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
123 		mss = max(mss, 68 - tcp_sk(sk)->tcp_header_len);
124 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
125 	}
126 	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
127 }
128 
129 
130 /**
131  *  retransmits_timed_out() - returns true if this connection has timed out
132  *  @sk:       The current socket
133  *  @boundary: max number of retransmissions
134  *  @timeout:  A custom timeout value.
135  *             If set to 0 the default timeout is calculated and used.
136  *             Using TCP_RTO_MIN and the number of unsuccessful retransmits.
137  *
138  * The default "timeout" value this function can calculate and use
139  * is equivalent to the timeout of a TCP Connection
140  * after "boundary" unsuccessful, exponentially backed-off
141  * retransmissions with an initial RTO of TCP_RTO_MIN.
142  */
143 static bool retransmits_timed_out(struct sock *sk,
144 				  unsigned int boundary,
145 				  unsigned int timeout)
146 {
147 	const unsigned int rto_base = TCP_RTO_MIN;
148 	unsigned int linear_backoff_thresh, start_ts;
149 
150 	if (!inet_csk(sk)->icsk_retransmits)
151 		return false;
152 
153 	start_ts = tcp_sk(sk)->retrans_stamp;
154 	if (unlikely(!start_ts)) {
155 		struct sk_buff *head = tcp_rtx_queue_head(sk);
156 
157 		if (!head)
158 			return false;
159 		start_ts = tcp_skb_timestamp(head);
160 	}
161 
162 	if (likely(timeout == 0)) {
163 		linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
164 
165 		if (boundary <= linear_backoff_thresh)
166 			timeout = ((2 << boundary) - 1) * rto_base;
167 		else
168 			timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
169 				(boundary - linear_backoff_thresh) * TCP_RTO_MAX;
170 	}
171 	return (tcp_time_stamp(tcp_sk(sk)) - start_ts) >= jiffies_to_msecs(timeout);
172 }
173 
174 /* A write timeout has occurred. Process the after effects. */
175 static int tcp_write_timeout(struct sock *sk)
176 {
177 	struct inet_connection_sock *icsk = inet_csk(sk);
178 	struct tcp_sock *tp = tcp_sk(sk);
179 	struct net *net = sock_net(sk);
180 	bool expired, do_reset;
181 	int retry_until;
182 
183 	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
184 		if (icsk->icsk_retransmits) {
185 			dst_negative_advice(sk);
186 			if (tp->syn_fastopen || tp->syn_data)
187 				tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
188 			if (tp->syn_data && icsk->icsk_retransmits == 1)
189 				NET_INC_STATS(sock_net(sk),
190 					      LINUX_MIB_TCPFASTOPENACTIVEFAIL);
191 		} else if (!tp->syn_data && !tp->syn_fastopen) {
192 			sk_rethink_txhash(sk);
193 		}
194 		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
195 		expired = icsk->icsk_retransmits >= retry_until;
196 	} else {
197 		if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {
198 			/* Some middle-boxes may black-hole Fast Open _after_
199 			 * the handshake. Therefore we conservatively disable
200 			 * Fast Open on this path on recurring timeouts after
201 			 * successful Fast Open.
202 			 */
203 			if (tp->syn_data_acked) {
204 				tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
205 				if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)
206 					NET_INC_STATS(sock_net(sk),
207 						      LINUX_MIB_TCPFASTOPENACTIVEFAIL);
208 			}
209 			/* Black hole detection */
210 			tcp_mtu_probing(icsk, sk);
211 
212 			dst_negative_advice(sk);
213 		} else {
214 			sk_rethink_txhash(sk);
215 		}
216 
217 		retry_until = net->ipv4.sysctl_tcp_retries2;
218 		if (sock_flag(sk, SOCK_DEAD)) {
219 			const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
220 
221 			retry_until = tcp_orphan_retries(sk, alive);
222 			do_reset = alive ||
223 				!retransmits_timed_out(sk, retry_until, 0);
224 
225 			if (tcp_out_of_resources(sk, do_reset))
226 				return 1;
227 		}
228 		expired = retransmits_timed_out(sk, retry_until,
229 						icsk->icsk_user_timeout);
230 	}
231 	if (expired) {
232 		/* Has it gone just too far? */
233 		tcp_write_err(sk);
234 		return 1;
235 	}
236 	return 0;
237 }
238 
239 /* Called with BH disabled */
240 void tcp_delack_timer_handler(struct sock *sk)
241 {
242 	struct inet_connection_sock *icsk = inet_csk(sk);
243 
244 	sk_mem_reclaim_partial(sk);
245 
246 	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
247 	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
248 		goto out;
249 
250 	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
251 		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
252 		goto out;
253 	}
254 	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
255 
256 	if (inet_csk_ack_scheduled(sk)) {
257 		if (!icsk->icsk_ack.pingpong) {
258 			/* Delayed ACK missed: inflate ATO. */
259 			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
260 		} else {
261 			/* Delayed ACK missed: leave pingpong mode and
262 			 * deflate ATO.
263 			 */
264 			icsk->icsk_ack.pingpong = 0;
265 			icsk->icsk_ack.ato      = TCP_ATO_MIN;
266 		}
267 		tcp_send_ack(sk);
268 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
269 	}
270 
271 out:
272 	if (tcp_under_memory_pressure(sk))
273 		sk_mem_reclaim(sk);
274 }
275 
276 
277 /**
278  *  tcp_delack_timer() - The TCP delayed ACK timeout handler
279  *  @data:  Pointer to the current socket. (gets casted to struct sock *)
280  *
281  *  This function gets (indirectly) called when the kernel timer for a TCP packet
282  *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
283  *
284  *  Returns: Nothing (void)
285  */
286 static void tcp_delack_timer(struct timer_list *t)
287 {
288 	struct inet_connection_sock *icsk =
289 			from_timer(icsk, t, icsk_delack_timer);
290 	struct sock *sk = &icsk->icsk_inet.sk;
291 
292 	bh_lock_sock(sk);
293 	if (!sock_owned_by_user(sk)) {
294 		tcp_delack_timer_handler(sk);
295 	} else {
296 		icsk->icsk_ack.blocked = 1;
297 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
298 		/* deleguate our work to tcp_release_cb() */
299 		if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
300 			sock_hold(sk);
301 	}
302 	bh_unlock_sock(sk);
303 	sock_put(sk);
304 }
305 
306 static void tcp_probe_timer(struct sock *sk)
307 {
308 	struct inet_connection_sock *icsk = inet_csk(sk);
309 	struct sk_buff *skb = tcp_send_head(sk);
310 	struct tcp_sock *tp = tcp_sk(sk);
311 	int max_probes;
312 	u32 start_ts;
313 
314 	if (tp->packets_out || !skb) {
315 		icsk->icsk_probes_out = 0;
316 		return;
317 	}
318 
319 	/* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
320 	 * long as the receiver continues to respond probes. We support this by
321 	 * default and reset icsk_probes_out with incoming ACKs. But if the
322 	 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
323 	 * kill the socket when the retry count and the time exceeds the
324 	 * corresponding system limit. We also implement similar policy when
325 	 * we use RTO to probe window in tcp_retransmit_timer().
326 	 */
327 	start_ts = tcp_skb_timestamp(skb);
328 	if (!start_ts)
329 		skb->skb_mstamp = tp->tcp_mstamp;
330 	else if (icsk->icsk_user_timeout &&
331 		 (s32)(tcp_time_stamp(tp) - start_ts) >
332 		 jiffies_to_msecs(icsk->icsk_user_timeout))
333 		goto abort;
334 
335 	max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
336 	if (sock_flag(sk, SOCK_DEAD)) {
337 		const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
338 
339 		max_probes = tcp_orphan_retries(sk, alive);
340 		if (!alive && icsk->icsk_backoff >= max_probes)
341 			goto abort;
342 		if (tcp_out_of_resources(sk, true))
343 			return;
344 	}
345 
346 	if (icsk->icsk_probes_out > max_probes) {
347 abort:		tcp_write_err(sk);
348 	} else {
349 		/* Only send another probe if we didn't close things up. */
350 		tcp_send_probe0(sk);
351 	}
352 }
353 
354 /*
355  *	Timer for Fast Open socket to retransmit SYNACK. Note that the
356  *	sk here is the child socket, not the parent (listener) socket.
357  */
358 static void tcp_fastopen_synack_timer(struct sock *sk)
359 {
360 	struct inet_connection_sock *icsk = inet_csk(sk);
361 	int max_retries = icsk->icsk_syn_retries ? :
362 	    sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
363 	struct request_sock *req;
364 
365 	req = tcp_sk(sk)->fastopen_rsk;
366 	req->rsk_ops->syn_ack_timeout(req);
367 
368 	if (req->num_timeout >= max_retries) {
369 		tcp_write_err(sk);
370 		return;
371 	}
372 	/* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
373 	 * returned from rtx_syn_ack() to make it more persistent like
374 	 * regular retransmit because if the child socket has been accepted
375 	 * it's not good to give up too easily.
376 	 */
377 	inet_rtx_syn_ack(sk, req);
378 	req->num_timeout++;
379 	icsk->icsk_retransmits++;
380 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
381 			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
382 }
383 
384 
385 /**
386  *  tcp_retransmit_timer() - The TCP retransmit timeout handler
387  *  @sk:  Pointer to the current socket.
388  *
389  *  This function gets called when the kernel timer for a TCP packet
390  *  of this socket expires.
391  *
392  *  It handles retransmission, timer adjustment and other necesarry measures.
393  *
394  *  Returns: Nothing (void)
395  */
396 void tcp_retransmit_timer(struct sock *sk)
397 {
398 	struct tcp_sock *tp = tcp_sk(sk);
399 	struct net *net = sock_net(sk);
400 	struct inet_connection_sock *icsk = inet_csk(sk);
401 
402 	if (tp->fastopen_rsk) {
403 		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
404 			     sk->sk_state != TCP_FIN_WAIT1);
405 		tcp_fastopen_synack_timer(sk);
406 		/* Before we receive ACK to our SYN-ACK don't retransmit
407 		 * anything else (e.g., data or FIN segments).
408 		 */
409 		return;
410 	}
411 	if (!tp->packets_out)
412 		goto out;
413 
414 	WARN_ON(tcp_rtx_queue_empty(sk));
415 
416 	tp->tlp_high_seq = 0;
417 
418 	if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
419 	    !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
420 		/* Receiver dastardly shrinks window. Our retransmits
421 		 * become zero probes, but we should not timeout this
422 		 * connection. If the socket is an orphan, time it out,
423 		 * we cannot allow such beasts to hang infinitely.
424 		 */
425 		struct inet_sock *inet = inet_sk(sk);
426 		if (sk->sk_family == AF_INET) {
427 			net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
428 					    &inet->inet_daddr,
429 					    ntohs(inet->inet_dport),
430 					    inet->inet_num,
431 					    tp->snd_una, tp->snd_nxt);
432 		}
433 #if IS_ENABLED(CONFIG_IPV6)
434 		else if (sk->sk_family == AF_INET6) {
435 			net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
436 					    &sk->sk_v6_daddr,
437 					    ntohs(inet->inet_dport),
438 					    inet->inet_num,
439 					    tp->snd_una, tp->snd_nxt);
440 		}
441 #endif
442 		if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {
443 			tcp_write_err(sk);
444 			goto out;
445 		}
446 		tcp_enter_loss(sk);
447 		tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1);
448 		__sk_dst_reset(sk);
449 		goto out_reset_timer;
450 	}
451 
452 	if (tcp_write_timeout(sk))
453 		goto out;
454 
455 	if (icsk->icsk_retransmits == 0) {
456 		int mib_idx;
457 
458 		if (icsk->icsk_ca_state == TCP_CA_Recovery) {
459 			if (tcp_is_sack(tp))
460 				mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
461 			else
462 				mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
463 		} else if (icsk->icsk_ca_state == TCP_CA_Loss) {
464 			mib_idx = LINUX_MIB_TCPLOSSFAILURES;
465 		} else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
466 			   tp->sacked_out) {
467 			if (tcp_is_sack(tp))
468 				mib_idx = LINUX_MIB_TCPSACKFAILURES;
469 			else
470 				mib_idx = LINUX_MIB_TCPRENOFAILURES;
471 		} else {
472 			mib_idx = LINUX_MIB_TCPTIMEOUTS;
473 		}
474 		__NET_INC_STATS(sock_net(sk), mib_idx);
475 	}
476 
477 	tcp_enter_loss(sk);
478 
479 	if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {
480 		/* Retransmission failed because of local congestion,
481 		 * do not backoff.
482 		 */
483 		if (!icsk->icsk_retransmits)
484 			icsk->icsk_retransmits = 1;
485 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
486 					  min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
487 					  TCP_RTO_MAX);
488 		goto out;
489 	}
490 
491 	/* Increase the timeout each time we retransmit.  Note that
492 	 * we do not increase the rtt estimate.  rto is initialized
493 	 * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
494 	 * that doubling rto each time is the least we can get away with.
495 	 * In KA9Q, Karn uses this for the first few times, and then
496 	 * goes to quadratic.  netBSD doubles, but only goes up to *64,
497 	 * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
498 	 * defined in the protocol as the maximum possible RTT.  I guess
499 	 * we'll have to use something other than TCP to talk to the
500 	 * University of Mars.
501 	 *
502 	 * PAWS allows us longer timeouts and large windows, so once
503 	 * implemented ftp to mars will work nicely. We will have to fix
504 	 * the 120 second clamps though!
505 	 */
506 	icsk->icsk_backoff++;
507 	icsk->icsk_retransmits++;
508 
509 out_reset_timer:
510 	/* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
511 	 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
512 	 * might be increased if the stream oscillates between thin and thick,
513 	 * thus the old value might already be too high compared to the value
514 	 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
515 	 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
516 	 * exponential backoff behaviour to avoid continue hammering
517 	 * linear-timeout retransmissions into a black hole
518 	 */
519 	if (sk->sk_state == TCP_ESTABLISHED &&
520 	    (tp->thin_lto || net->ipv4.sysctl_tcp_thin_linear_timeouts) &&
521 	    tcp_stream_is_thin(tp) &&
522 	    icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
523 		icsk->icsk_backoff = 0;
524 		icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
525 	} else {
526 		/* Use normal (exponential) backoff */
527 		icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
528 	}
529 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
530 	if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0))
531 		__sk_dst_reset(sk);
532 
533 out:;
534 }
535 
536 /* Called with bottom-half processing disabled.
537    Called by tcp_write_timer() */
538 void tcp_write_timer_handler(struct sock *sk)
539 {
540 	struct inet_connection_sock *icsk = inet_csk(sk);
541 	int event;
542 
543 	if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
544 	    !icsk->icsk_pending)
545 		goto out;
546 
547 	if (time_after(icsk->icsk_timeout, jiffies)) {
548 		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
549 		goto out;
550 	}
551 
552 	tcp_mstamp_refresh(tcp_sk(sk));
553 	event = icsk->icsk_pending;
554 
555 	switch (event) {
556 	case ICSK_TIME_REO_TIMEOUT:
557 		tcp_rack_reo_timeout(sk);
558 		break;
559 	case ICSK_TIME_LOSS_PROBE:
560 		tcp_send_loss_probe(sk);
561 		break;
562 	case ICSK_TIME_RETRANS:
563 		icsk->icsk_pending = 0;
564 		tcp_retransmit_timer(sk);
565 		break;
566 	case ICSK_TIME_PROBE0:
567 		icsk->icsk_pending = 0;
568 		tcp_probe_timer(sk);
569 		break;
570 	}
571 
572 out:
573 	sk_mem_reclaim(sk);
574 }
575 
576 static void tcp_write_timer(struct timer_list *t)
577 {
578 	struct inet_connection_sock *icsk =
579 			from_timer(icsk, t, icsk_retransmit_timer);
580 	struct sock *sk = &icsk->icsk_inet.sk;
581 
582 	bh_lock_sock(sk);
583 	if (!sock_owned_by_user(sk)) {
584 		tcp_write_timer_handler(sk);
585 	} else {
586 		/* delegate our work to tcp_release_cb() */
587 		if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))
588 			sock_hold(sk);
589 	}
590 	bh_unlock_sock(sk);
591 	sock_put(sk);
592 }
593 
594 void tcp_syn_ack_timeout(const struct request_sock *req)
595 {
596 	struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
597 
598 	__NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
599 }
600 EXPORT_SYMBOL(tcp_syn_ack_timeout);
601 
602 void tcp_set_keepalive(struct sock *sk, int val)
603 {
604 	if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
605 		return;
606 
607 	if (val && !sock_flag(sk, SOCK_KEEPOPEN))
608 		inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
609 	else if (!val)
610 		inet_csk_delete_keepalive_timer(sk);
611 }
612 EXPORT_SYMBOL_GPL(tcp_set_keepalive);
613 
614 
615 static void tcp_keepalive_timer (struct timer_list *t)
616 {
617 	struct sock *sk = from_timer(sk, t, sk_timer);
618 	struct inet_connection_sock *icsk = inet_csk(sk);
619 	struct tcp_sock *tp = tcp_sk(sk);
620 	u32 elapsed;
621 
622 	/* Only process if socket is not in use. */
623 	bh_lock_sock(sk);
624 	if (sock_owned_by_user(sk)) {
625 		/* Try again later. */
626 		inet_csk_reset_keepalive_timer (sk, HZ/20);
627 		goto out;
628 	}
629 
630 	if (sk->sk_state == TCP_LISTEN) {
631 		pr_err("Hmm... keepalive on a LISTEN ???\n");
632 		goto out;
633 	}
634 
635 	if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
636 		if (tp->linger2 >= 0) {
637 			const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
638 
639 			if (tmo > 0) {
640 				tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
641 				goto out;
642 			}
643 		}
644 		tcp_send_active_reset(sk, GFP_ATOMIC);
645 		goto death;
646 	}
647 
648 	if (!sock_flag(sk, SOCK_KEEPOPEN) ||
649 	    ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
650 		goto out;
651 
652 	elapsed = keepalive_time_when(tp);
653 
654 	/* It is alive without keepalive 8) */
655 	if (tp->packets_out || !tcp_write_queue_empty(sk))
656 		goto resched;
657 
658 	elapsed = keepalive_time_elapsed(tp);
659 
660 	if (elapsed >= keepalive_time_when(tp)) {
661 		/* If the TCP_USER_TIMEOUT option is enabled, use that
662 		 * to determine when to timeout instead.
663 		 */
664 		if ((icsk->icsk_user_timeout != 0 &&
665 		    elapsed >= icsk->icsk_user_timeout &&
666 		    icsk->icsk_probes_out > 0) ||
667 		    (icsk->icsk_user_timeout == 0 &&
668 		    icsk->icsk_probes_out >= keepalive_probes(tp))) {
669 			tcp_send_active_reset(sk, GFP_ATOMIC);
670 			tcp_write_err(sk);
671 			goto out;
672 		}
673 		if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
674 			icsk->icsk_probes_out++;
675 			elapsed = keepalive_intvl_when(tp);
676 		} else {
677 			/* If keepalive was lost due to local congestion,
678 			 * try harder.
679 			 */
680 			elapsed = TCP_RESOURCE_PROBE_INTERVAL;
681 		}
682 	} else {
683 		/* It is tp->rcv_tstamp + keepalive_time_when(tp) */
684 		elapsed = keepalive_time_when(tp) - elapsed;
685 	}
686 
687 	sk_mem_reclaim(sk);
688 
689 resched:
690 	inet_csk_reset_keepalive_timer (sk, elapsed);
691 	goto out;
692 
693 death:
694 	tcp_done(sk);
695 
696 out:
697 	bh_unlock_sock(sk);
698 	sock_put(sk);
699 }
700 
701 void tcp_init_xmit_timers(struct sock *sk)
702 {
703 	inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
704 				  &tcp_keepalive_timer);
705 	hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,
706 		     HRTIMER_MODE_ABS_PINNED);
707 	tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;
708 }
709