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>
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
27 * Linus Torvalds : send_delayed_ack
28 * David S. Miller : Charge memory using the right skb
29 * during syn/ack processing.
30 * David S. Miller : Output engine completely rewritten.
31 * Andrea Arcangeli: SYNACK carry ts_recent in tsecr.
32 * Cacophonix Gaul : draft-minshall-nagle-01
33 * J Hadi Salim : ECN support
37 #define pr_fmt(fmt) "TCP: " fmt
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly = 1;
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
53 /* Default TSQ limit of two TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 131072;
56 /* This limits the percentage of the congestion window which we
57 * will allow a single TSO frame to consume. Building TSO frames
58 * which are too large can cause TCP streams to be bursty.
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
65 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
66 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
69 int push_one, gfp_t gfp);
71 /* Account for new data that has been sent to the network. */
72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
74 struct inet_connection_sock *icsk = inet_csk(sk);
75 struct tcp_sock *tp = tcp_sk(sk);
76 unsigned int prior_packets = tp->packets_out;
78 tcp_advance_send_head(sk, skb);
79 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
81 tp->packets_out += tcp_skb_pcount(skb);
82 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
83 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
87 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
91 /* SND.NXT, if window was not shrunk.
92 * If window has been shrunk, what should we make? It is not clear at all.
93 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-(
94 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already
95 * invalid. OK, let's make this for now:
97 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
99 const struct tcp_sock *tp = tcp_sk(sk);
101 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
104 return tcp_wnd_end(tp);
107 /* Calculate mss to advertise in SYN segment.
108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
110 * 1. It is independent of path mtu.
111 * 2. Ideally, it is maximal possible segment size i.e. 65535-40.
112 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of
113 * attached devices, because some buggy hosts are confused by
115 * 4. We do not make 3, we advertise MSS, calculated from first
116 * hop device mtu, but allow to raise it to ip_rt_min_advmss.
117 * This may be overridden via information stored in routing table.
118 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible,
119 * probably even Jumbo".
121 static __u16 tcp_advertise_mss(struct sock *sk)
123 struct tcp_sock *tp = tcp_sk(sk);
124 const struct dst_entry *dst = __sk_dst_get(sk);
125 int mss = tp->advmss;
128 unsigned int metric = dst_metric_advmss(dst);
139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
140 * This is the first part of cwnd validation mechanism. */
141 static void tcp_cwnd_restart(struct sock *sk, const struct dst_entry *dst)
143 struct tcp_sock *tp = tcp_sk(sk);
144 s32 delta = tcp_time_stamp - tp->lsndtime;
145 u32 restart_cwnd = tcp_init_cwnd(tp, dst);
146 u32 cwnd = tp->snd_cwnd;
148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
150 tp->snd_ssthresh = tcp_current_ssthresh(sk);
151 restart_cwnd = min(restart_cwnd, cwnd);
153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
155 tp->snd_cwnd = max(cwnd, restart_cwnd);
156 tp->snd_cwnd_stamp = tcp_time_stamp;
157 tp->snd_cwnd_used = 0;
160 /* Congestion state accounting after a packet has been sent. */
161 static void tcp_event_data_sent(struct tcp_sock *tp,
164 struct inet_connection_sock *icsk = inet_csk(sk);
165 const u32 now = tcp_time_stamp;
166 const struct dst_entry *dst = __sk_dst_get(sk);
168 if (sysctl_tcp_slow_start_after_idle &&
169 (!tp->packets_out && (s32)(now - tp->lsndtime) > icsk->icsk_rto))
170 tcp_cwnd_restart(sk, __sk_dst_get(sk));
174 /* If it is a reply for ato after last received
175 * packet, enter pingpong mode.
177 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato &&
178 (!dst || !dst_metric(dst, RTAX_QUICKACK)))
179 icsk->icsk_ack.pingpong = 1;
182 /* Account for an ACK we sent. */
183 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
185 tcp_dec_quickack_mode(sk, pkts);
186 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
190 u32 tcp_default_init_rwnd(u32 mss)
192 /* Initial receive window should be twice of TCP_INIT_CWND to
193 * enable proper sending of new unsent data during fast recovery
194 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
195 * limit when mss is larger than 1460.
197 u32 init_rwnd = TCP_INIT_CWND * 2;
200 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
204 /* Determine a window scaling and initial window to offer.
205 * Based on the assumption that the given amount of space
206 * will be offered. Store the results in the tp structure.
207 * NOTE: for smooth operation initial space offering should
208 * be a multiple of mss if possible. We assume here that mss >= 1.
209 * This MUST be enforced by all callers.
211 void tcp_select_initial_window(int __space, __u32 mss,
212 __u32 *rcv_wnd, __u32 *window_clamp,
213 int wscale_ok, __u8 *rcv_wscale,
216 unsigned int space = (__space < 0 ? 0 : __space);
218 /* If no clamp set the clamp to the max possible scaled window */
219 if (*window_clamp == 0)
220 (*window_clamp) = (65535 << 14);
221 space = min(*window_clamp, space);
223 /* Quantize space offering to a multiple of mss if possible. */
225 space = (space / mss) * mss;
227 /* NOTE: offering an initial window larger than 32767
228 * will break some buggy TCP stacks. If the admin tells us
229 * it is likely we could be speaking with such a buggy stack
230 * we will truncate our initial window offering to 32K-1
231 * unless the remote has sent us a window scaling option,
232 * which we interpret as a sign the remote TCP is not
233 * misinterpreting the window field as a signed quantity.
235 if (sysctl_tcp_workaround_signed_windows)
236 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
242 /* Set window scaling on max possible window
243 * See RFC1323 for an explanation of the limit to 14
245 space = max_t(u32, sysctl_tcp_rmem[2], sysctl_rmem_max);
246 space = min_t(u32, space, *window_clamp);
247 while (space > 65535 && (*rcv_wscale) < 14) {
253 if (mss > (1 << *rcv_wscale)) {
254 if (!init_rcv_wnd) /* Use default unless specified otherwise */
255 init_rcv_wnd = tcp_default_init_rwnd(mss);
256 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
259 /* Set the clamp no higher than max representable value */
260 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
262 EXPORT_SYMBOL(tcp_select_initial_window);
264 /* Chose a new window to advertise, update state in tcp_sock for the
265 * socket, and return result with RFC1323 scaling applied. The return
266 * value can be stuffed directly into th->window for an outgoing
269 static u16 tcp_select_window(struct sock *sk)
271 struct tcp_sock *tp = tcp_sk(sk);
272 u32 old_win = tp->rcv_wnd;
273 u32 cur_win = tcp_receive_window(tp);
274 u32 new_win = __tcp_select_window(sk);
276 /* Never shrink the offered window */
277 if (new_win < cur_win) {
278 /* Danger Will Robinson!
279 * Don't update rcv_wup/rcv_wnd here or else
280 * we will not be able to advertise a zero
281 * window in time. --DaveM
283 * Relax Will Robinson.
286 NET_INC_STATS(sock_net(sk),
287 LINUX_MIB_TCPWANTZEROWINDOWADV);
288 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
290 tp->rcv_wnd = new_win;
291 tp->rcv_wup = tp->rcv_nxt;
293 /* Make sure we do not exceed the maximum possible
296 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
297 new_win = min(new_win, MAX_TCP_WINDOW);
299 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
301 /* RFC1323 scaling applied */
302 new_win >>= tp->rx_opt.rcv_wscale;
304 /* If we advertise zero window, disable fast path. */
308 NET_INC_STATS(sock_net(sk),
309 LINUX_MIB_TCPTOZEROWINDOWADV);
310 } else if (old_win == 0) {
311 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
317 /* Packet ECN state for a SYN-ACK */
318 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
320 const struct tcp_sock *tp = tcp_sk(sk);
322 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
323 if (!(tp->ecn_flags & TCP_ECN_OK))
324 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
325 else if (tcp_ca_needs_ecn(sk))
329 /* Packet ECN state for a SYN. */
330 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
332 struct tcp_sock *tp = tcp_sk(sk);
333 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
334 tcp_ca_needs_ecn(sk);
337 const struct dst_entry *dst = __sk_dst_get(sk);
339 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
346 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
347 tp->ecn_flags = TCP_ECN_OK;
348 if (tcp_ca_needs_ecn(sk))
354 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th,
357 if (inet_rsk(req)->ecn_ok) {
359 if (tcp_ca_needs_ecn(sk))
364 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
367 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
370 struct tcp_sock *tp = tcp_sk(sk);
372 if (tp->ecn_flags & TCP_ECN_OK) {
373 /* Not-retransmitted data segment: set ECT and inject CWR. */
374 if (skb->len != tcp_header_len &&
375 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
377 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
378 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
379 tcp_hdr(skb)->cwr = 1;
380 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
382 } else if (!tcp_ca_needs_ecn(sk)) {
383 /* ACK or retransmitted segment: clear ECT|CE */
384 INET_ECN_dontxmit(sk);
386 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
387 tcp_hdr(skb)->ece = 1;
391 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
392 * auto increment end seqno.
394 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
396 struct skb_shared_info *shinfo = skb_shinfo(skb);
398 skb->ip_summed = CHECKSUM_PARTIAL;
401 TCP_SKB_CB(skb)->tcp_flags = flags;
402 TCP_SKB_CB(skb)->sacked = 0;
404 tcp_skb_pcount_set(skb, 1);
405 shinfo->gso_size = 0;
406 shinfo->gso_type = 0;
408 TCP_SKB_CB(skb)->seq = seq;
409 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
411 TCP_SKB_CB(skb)->end_seq = seq;
414 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
416 return tp->snd_una != tp->snd_up;
419 #define OPTION_SACK_ADVERTISE (1 << 0)
420 #define OPTION_TS (1 << 1)
421 #define OPTION_MD5 (1 << 2)
422 #define OPTION_WSCALE (1 << 3)
423 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
425 struct tcp_out_options {
426 u16 options; /* bit field of OPTION_* */
427 u16 mss; /* 0 to disable */
428 u8 ws; /* window scale, 0 to disable */
429 u8 num_sack_blocks; /* number of SACK blocks to include */
430 u8 hash_size; /* bytes in hash_location */
431 __u8 *hash_location; /* temporary pointer, overloaded */
432 __u32 tsval, tsecr; /* need to include OPTION_TS */
433 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
436 /* Write previously computed TCP options to the packet.
438 * Beware: Something in the Internet is very sensitive to the ordering of
439 * TCP options, we learned this through the hard way, so be careful here.
440 * Luckily we can at least blame others for their non-compliance but from
441 * inter-operability perspective it seems that we're somewhat stuck with
442 * the ordering which we have been using if we want to keep working with
443 * those broken things (not that it currently hurts anybody as there isn't
444 * particular reason why the ordering would need to be changed).
446 * At least SACK_PERM as the first option is known to lead to a disaster
447 * (but it may well be that other scenarios fail similarly).
449 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
450 struct tcp_out_options *opts)
452 u16 options = opts->options; /* mungable copy */
454 if (unlikely(OPTION_MD5 & options)) {
455 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
456 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
457 /* overload cookie hash location */
458 opts->hash_location = (__u8 *)ptr;
462 if (unlikely(opts->mss)) {
463 *ptr++ = htonl((TCPOPT_MSS << 24) |
464 (TCPOLEN_MSS << 16) |
468 if (likely(OPTION_TS & options)) {
469 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
470 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
471 (TCPOLEN_SACK_PERM << 16) |
472 (TCPOPT_TIMESTAMP << 8) |
474 options &= ~OPTION_SACK_ADVERTISE;
476 *ptr++ = htonl((TCPOPT_NOP << 24) |
478 (TCPOPT_TIMESTAMP << 8) |
481 *ptr++ = htonl(opts->tsval);
482 *ptr++ = htonl(opts->tsecr);
485 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
486 *ptr++ = htonl((TCPOPT_NOP << 24) |
488 (TCPOPT_SACK_PERM << 8) |
492 if (unlikely(OPTION_WSCALE & options)) {
493 *ptr++ = htonl((TCPOPT_NOP << 24) |
494 (TCPOPT_WINDOW << 16) |
495 (TCPOLEN_WINDOW << 8) |
499 if (unlikely(opts->num_sack_blocks)) {
500 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
501 tp->duplicate_sack : tp->selective_acks;
504 *ptr++ = htonl((TCPOPT_NOP << 24) |
507 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
508 TCPOLEN_SACK_PERBLOCK)));
510 for (this_sack = 0; this_sack < opts->num_sack_blocks;
512 *ptr++ = htonl(sp[this_sack].start_seq);
513 *ptr++ = htonl(sp[this_sack].end_seq);
516 tp->rx_opt.dsack = 0;
519 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
520 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
522 *ptr++ = htonl((TCPOPT_EXP << 24) |
523 ((TCPOLEN_EXP_FASTOPEN_BASE + foc->len) << 16) |
524 TCPOPT_FASTOPEN_MAGIC);
526 memcpy(ptr, foc->val, foc->len);
527 if ((foc->len & 3) == 2) {
528 u8 *align = ((u8 *)ptr) + foc->len;
529 align[0] = align[1] = TCPOPT_NOP;
531 ptr += (foc->len + 3) >> 2;
535 /* Compute TCP options for SYN packets. This is not the final
536 * network wire format yet.
538 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
539 struct tcp_out_options *opts,
540 struct tcp_md5sig_key **md5)
542 struct tcp_sock *tp = tcp_sk(sk);
543 unsigned int remaining = MAX_TCP_OPTION_SPACE;
544 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
546 #ifdef CONFIG_TCP_MD5SIG
547 *md5 = tp->af_specific->md5_lookup(sk, sk);
549 opts->options |= OPTION_MD5;
550 remaining -= TCPOLEN_MD5SIG_ALIGNED;
556 /* We always get an MSS option. The option bytes which will be seen in
557 * normal data packets should timestamps be used, must be in the MSS
558 * advertised. But we subtract them from tp->mss_cache so that
559 * calculations in tcp_sendmsg are simpler etc. So account for this
560 * fact here if necessary. If we don't do this correctly, as a
561 * receiver we won't recognize data packets as being full sized when we
562 * should, and thus we won't abide by the delayed ACK rules correctly.
563 * SACKs don't matter, we never delay an ACK when we have any of those
565 opts->mss = tcp_advertise_mss(sk);
566 remaining -= TCPOLEN_MSS_ALIGNED;
568 if (likely(sysctl_tcp_timestamps && *md5 == NULL)) {
569 opts->options |= OPTION_TS;
570 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
571 opts->tsecr = tp->rx_opt.ts_recent;
572 remaining -= TCPOLEN_TSTAMP_ALIGNED;
574 if (likely(sysctl_tcp_window_scaling)) {
575 opts->ws = tp->rx_opt.rcv_wscale;
576 opts->options |= OPTION_WSCALE;
577 remaining -= TCPOLEN_WSCALE_ALIGNED;
579 if (likely(sysctl_tcp_sack)) {
580 opts->options |= OPTION_SACK_ADVERTISE;
581 if (unlikely(!(OPTION_TS & opts->options)))
582 remaining -= TCPOLEN_SACKPERM_ALIGNED;
585 if (fastopen && fastopen->cookie.len >= 0) {
586 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + fastopen->cookie.len;
587 need = (need + 3) & ~3U; /* Align to 32 bits */
588 if (remaining >= need) {
589 opts->options |= OPTION_FAST_OPEN_COOKIE;
590 opts->fastopen_cookie = &fastopen->cookie;
592 tp->syn_fastopen = 1;
596 return MAX_TCP_OPTION_SPACE - remaining;
599 /* Set up TCP options for SYN-ACKs. */
600 static unsigned int tcp_synack_options(struct sock *sk,
601 struct request_sock *req,
602 unsigned int mss, struct sk_buff *skb,
603 struct tcp_out_options *opts,
604 struct tcp_md5sig_key **md5,
605 struct tcp_fastopen_cookie *foc)
607 struct inet_request_sock *ireq = inet_rsk(req);
608 unsigned int remaining = MAX_TCP_OPTION_SPACE;
610 #ifdef CONFIG_TCP_MD5SIG
611 *md5 = tcp_rsk(req)->af_specific->md5_lookup(sk, req);
613 opts->options |= OPTION_MD5;
614 remaining -= TCPOLEN_MD5SIG_ALIGNED;
616 /* We can't fit any SACK blocks in a packet with MD5 + TS
617 * options. There was discussion about disabling SACK
618 * rather than TS in order to fit in better with old,
619 * buggy kernels, but that was deemed to be unnecessary.
621 ireq->tstamp_ok &= !ireq->sack_ok;
627 /* We always send an MSS option. */
629 remaining -= TCPOLEN_MSS_ALIGNED;
631 if (likely(ireq->wscale_ok)) {
632 opts->ws = ireq->rcv_wscale;
633 opts->options |= OPTION_WSCALE;
634 remaining -= TCPOLEN_WSCALE_ALIGNED;
636 if (likely(ireq->tstamp_ok)) {
637 opts->options |= OPTION_TS;
638 opts->tsval = tcp_skb_timestamp(skb);
639 opts->tsecr = req->ts_recent;
640 remaining -= TCPOLEN_TSTAMP_ALIGNED;
642 if (likely(ireq->sack_ok)) {
643 opts->options |= OPTION_SACK_ADVERTISE;
644 if (unlikely(!ireq->tstamp_ok))
645 remaining -= TCPOLEN_SACKPERM_ALIGNED;
647 if (foc != NULL && foc->len >= 0) {
648 u32 need = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
649 need = (need + 3) & ~3U; /* Align to 32 bits */
650 if (remaining >= need) {
651 opts->options |= OPTION_FAST_OPEN_COOKIE;
652 opts->fastopen_cookie = foc;
657 return MAX_TCP_OPTION_SPACE - remaining;
660 /* Compute TCP options for ESTABLISHED sockets. This is not the
661 * final wire format yet.
663 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
664 struct tcp_out_options *opts,
665 struct tcp_md5sig_key **md5)
667 struct tcp_sock *tp = tcp_sk(sk);
668 unsigned int size = 0;
669 unsigned int eff_sacks;
673 #ifdef CONFIG_TCP_MD5SIG
674 *md5 = tp->af_specific->md5_lookup(sk, sk);
675 if (unlikely(*md5)) {
676 opts->options |= OPTION_MD5;
677 size += TCPOLEN_MD5SIG_ALIGNED;
683 if (likely(tp->rx_opt.tstamp_ok)) {
684 opts->options |= OPTION_TS;
685 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
686 opts->tsecr = tp->rx_opt.ts_recent;
687 size += TCPOLEN_TSTAMP_ALIGNED;
690 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
691 if (unlikely(eff_sacks)) {
692 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
693 opts->num_sack_blocks =
694 min_t(unsigned int, eff_sacks,
695 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
696 TCPOLEN_SACK_PERBLOCK);
697 size += TCPOLEN_SACK_BASE_ALIGNED +
698 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
705 /* TCP SMALL QUEUES (TSQ)
707 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
708 * to reduce RTT and bufferbloat.
709 * We do this using a special skb destructor (tcp_wfree).
711 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
712 * needs to be reallocated in a driver.
713 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
715 * Since transmit from skb destructor is forbidden, we use a tasklet
716 * to process all sockets that eventually need to send more skbs.
717 * We use one tasklet per cpu, with its own queue of sockets.
720 struct tasklet_struct tasklet;
721 struct list_head head; /* queue of tcp sockets */
723 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
725 static void tcp_tsq_handler(struct sock *sk)
727 if ((1 << sk->sk_state) &
728 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
729 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
730 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
734 * One tasklet per cpu tries to send more skbs.
735 * We run in tasklet context but need to disable irqs when
736 * transferring tsq->head because tcp_wfree() might
737 * interrupt us (non NAPI drivers)
739 static void tcp_tasklet_func(unsigned long data)
741 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
744 struct list_head *q, *n;
748 local_irq_save(flags);
749 list_splice_init(&tsq->head, &list);
750 local_irq_restore(flags);
752 list_for_each_safe(q, n, &list) {
753 tp = list_entry(q, struct tcp_sock, tsq_node);
754 list_del(&tp->tsq_node);
756 sk = (struct sock *)tp;
759 if (!sock_owned_by_user(sk)) {
762 /* defer the work to tcp_release_cb() */
763 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
767 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
772 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
773 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
774 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
775 (1UL << TCP_MTU_REDUCED_DEFERRED))
777 * tcp_release_cb - tcp release_sock() callback
780 * called from release_sock() to perform protocol dependent
781 * actions before socket release.
783 void tcp_release_cb(struct sock *sk)
785 struct tcp_sock *tp = tcp_sk(sk);
786 unsigned long flags, nflags;
788 /* perform an atomic operation only if at least one flag is set */
790 flags = tp->tsq_flags;
791 if (!(flags & TCP_DEFERRED_ALL))
793 nflags = flags & ~TCP_DEFERRED_ALL;
794 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
796 if (flags & (1UL << TCP_TSQ_DEFERRED))
799 /* Here begins the tricky part :
800 * We are called from release_sock() with :
802 * 2) sk_lock.slock spinlock held
803 * 3) socket owned by us (sk->sk_lock.owned == 1)
805 * But following code is meant to be called from BH handlers,
806 * so we should keep BH disabled, but early release socket ownership
808 sock_release_ownership(sk);
810 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
811 tcp_write_timer_handler(sk);
814 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
815 tcp_delack_timer_handler(sk);
818 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
819 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
823 EXPORT_SYMBOL(tcp_release_cb);
825 void __init tcp_tasklet_init(void)
829 for_each_possible_cpu(i) {
830 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
832 INIT_LIST_HEAD(&tsq->head);
833 tasklet_init(&tsq->tasklet,
840 * Write buffer destructor automatically called from kfree_skb.
841 * We can't xmit new skbs from this context, as we might already
844 void tcp_wfree(struct sk_buff *skb)
846 struct sock *sk = skb->sk;
847 struct tcp_sock *tp = tcp_sk(sk);
850 /* Keep one reference on sk_wmem_alloc.
851 * Will be released by sk_free() from here or tcp_tasklet_func()
853 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
855 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
856 * Wait until our queues (qdisc + devices) are drained.
858 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
859 * - chance for incoming ACK (processed by another cpu maybe)
860 * to migrate this flow (skb->ooo_okay will be eventually set)
862 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
865 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
866 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
868 struct tsq_tasklet *tsq;
870 /* queue this socket to tasklet queue */
871 local_irq_save(flags);
872 tsq = this_cpu_ptr(&tsq_tasklet);
873 list_add(&tp->tsq_node, &tsq->head);
874 tasklet_schedule(&tsq->tasklet);
875 local_irq_restore(flags);
882 /* This routine actually transmits TCP packets queued in by
883 * tcp_do_sendmsg(). This is used by both the initial
884 * transmission and possible later retransmissions.
885 * All SKB's seen here are completely headerless. It is our
886 * job to build the TCP header, and pass the packet down to
887 * IP so it can do the same plus pass the packet off to the
890 * We are working here with either a clone of the original
891 * SKB, or a fresh unique copy made by the retransmit engine.
893 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
896 const struct inet_connection_sock *icsk = inet_csk(sk);
897 struct inet_sock *inet;
899 struct tcp_skb_cb *tcb;
900 struct tcp_out_options opts;
901 unsigned int tcp_options_size, tcp_header_size;
902 struct tcp_md5sig_key *md5;
906 BUG_ON(!skb || !tcp_skb_pcount(skb));
909 skb_mstamp_get(&skb->skb_mstamp);
911 if (unlikely(skb_cloned(skb)))
912 skb = pskb_copy(skb, gfp_mask);
914 skb = skb_clone(skb, gfp_mask);
921 tcb = TCP_SKB_CB(skb);
922 memset(&opts, 0, sizeof(opts));
924 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
925 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
927 tcp_options_size = tcp_established_options(sk, skb, &opts,
929 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
931 if (tcp_packets_in_flight(tp) == 0)
932 tcp_ca_event(sk, CA_EVENT_TX_START);
934 /* if no packet is in qdisc/device queue, then allow XPS to select
935 * another queue. We can be called from tcp_tsq_handler()
936 * which holds one reference to sk_wmem_alloc.
938 * TODO: Ideally, in-flight pure ACK packets should not matter here.
939 * One way to get this would be to set skb->truesize = 2 on them.
941 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
943 skb_push(skb, tcp_header_size);
944 skb_reset_transport_header(skb);
948 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
949 skb_set_hash_from_sk(skb, sk);
950 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
952 /* Build TCP header and checksum it. */
954 th->source = inet->inet_sport;
955 th->dest = inet->inet_dport;
956 th->seq = htonl(tcb->seq);
957 th->ack_seq = htonl(tp->rcv_nxt);
958 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
961 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
962 /* RFC1323: The window in SYN & SYN/ACK segments
965 th->window = htons(min(tp->rcv_wnd, 65535U));
967 th->window = htons(tcp_select_window(sk));
972 /* The urg_mode check is necessary during a below snd_una win probe */
973 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
974 if (before(tp->snd_up, tcb->seq + 0x10000)) {
975 th->urg_ptr = htons(tp->snd_up - tcb->seq);
977 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
978 th->urg_ptr = htons(0xFFFF);
983 tcp_options_write((__be32 *)(th + 1), tp, &opts);
984 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
985 tcp_ecn_send(sk, skb, tcp_header_size);
987 #ifdef CONFIG_TCP_MD5SIG
988 /* Calculate the MD5 hash, as we have all we need now */
990 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
991 tp->af_specific->calc_md5_hash(opts.hash_location,
996 icsk->icsk_af_ops->send_check(sk, skb);
998 if (likely(tcb->tcp_flags & TCPHDR_ACK))
999 tcp_event_ack_sent(sk, tcp_skb_pcount(skb));
1001 if (skb->len != tcp_header_size)
1002 tcp_event_data_sent(tp, sk);
1004 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1005 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1006 tcp_skb_pcount(skb));
1008 /* OK, its time to fill skb_shinfo(skb)->gso_segs */
1009 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1011 /* Our usage of tstamp should remain private */
1012 skb->tstamp.tv64 = 0;
1014 /* Cleanup our debris for IP stacks */
1015 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1016 sizeof(struct inet6_skb_parm)));
1018 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1020 if (likely(err <= 0))
1025 return net_xmit_eval(err);
1028 /* This routine just queues the buffer for sending.
1030 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1031 * otherwise socket can stall.
1033 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1035 struct tcp_sock *tp = tcp_sk(sk);
1037 /* Advance write_seq and place onto the write_queue. */
1038 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1039 __skb_header_release(skb);
1040 tcp_add_write_queue_tail(sk, skb);
1041 sk->sk_wmem_queued += skb->truesize;
1042 sk_mem_charge(sk, skb->truesize);
1045 /* Initialize TSO segments for a packet. */
1046 static void tcp_set_skb_tso_segs(const struct sock *sk, struct sk_buff *skb,
1047 unsigned int mss_now)
1049 struct skb_shared_info *shinfo = skb_shinfo(skb);
1051 /* Make sure we own this skb before messing gso_size/gso_segs */
1052 WARN_ON_ONCE(skb_cloned(skb));
1054 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1055 /* Avoid the costly divide in the normal
1058 tcp_skb_pcount_set(skb, 1);
1059 shinfo->gso_size = 0;
1060 shinfo->gso_type = 0;
1062 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1063 shinfo->gso_size = mss_now;
1064 shinfo->gso_type = sk->sk_gso_type;
1068 /* When a modification to fackets out becomes necessary, we need to check
1069 * skb is counted to fackets_out or not.
1071 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1074 struct tcp_sock *tp = tcp_sk(sk);
1076 if (!tp->sacked_out || tcp_is_reno(tp))
1079 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1080 tp->fackets_out -= decr;
1083 /* Pcount in the middle of the write queue got changed, we need to do various
1084 * tweaks to fix counters
1086 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1088 struct tcp_sock *tp = tcp_sk(sk);
1090 tp->packets_out -= decr;
1092 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1093 tp->sacked_out -= decr;
1094 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1095 tp->retrans_out -= decr;
1096 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1097 tp->lost_out -= decr;
1099 /* Reno case is special. Sigh... */
1100 if (tcp_is_reno(tp) && decr > 0)
1101 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1103 tcp_adjust_fackets_out(sk, skb, decr);
1105 if (tp->lost_skb_hint &&
1106 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1107 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1108 tp->lost_cnt_hint -= decr;
1110 tcp_verify_left_out(tp);
1113 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1115 struct skb_shared_info *shinfo = skb_shinfo(skb);
1117 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1118 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1119 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1120 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1122 shinfo->tx_flags &= ~tsflags;
1123 shinfo2->tx_flags |= tsflags;
1124 swap(shinfo->tskey, shinfo2->tskey);
1128 /* Function to create two new TCP segments. Shrinks the given segment
1129 * to the specified size and appends a new segment with the rest of the
1130 * packet to the list. This won't be called frequently, I hope.
1131 * Remember, these are still headerless SKBs at this point.
1133 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1134 unsigned int mss_now, gfp_t gfp)
1136 struct tcp_sock *tp = tcp_sk(sk);
1137 struct sk_buff *buff;
1138 int nsize, old_factor;
1142 if (WARN_ON(len > skb->len))
1145 nsize = skb_headlen(skb) - len;
1149 if (skb_unclone(skb, gfp))
1152 /* Get a new skb... force flag on. */
1153 buff = sk_stream_alloc_skb(sk, nsize, gfp);
1155 return -ENOMEM; /* We'll just try again later. */
1157 sk->sk_wmem_queued += buff->truesize;
1158 sk_mem_charge(sk, buff->truesize);
1159 nlen = skb->len - len - nsize;
1160 buff->truesize += nlen;
1161 skb->truesize -= nlen;
1163 /* Correct the sequence numbers. */
1164 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1165 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1166 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1168 /* PSH and FIN should only be set in the second packet. */
1169 flags = TCP_SKB_CB(skb)->tcp_flags;
1170 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1171 TCP_SKB_CB(buff)->tcp_flags = flags;
1172 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1174 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1175 /* Copy and checksum data tail into the new buffer. */
1176 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1177 skb_put(buff, nsize),
1182 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1184 skb->ip_summed = CHECKSUM_PARTIAL;
1185 skb_split(skb, buff, len);
1188 buff->ip_summed = skb->ip_summed;
1190 buff->tstamp = skb->tstamp;
1191 tcp_fragment_tstamp(skb, buff);
1193 old_factor = tcp_skb_pcount(skb);
1195 /* Fix up tso_factor for both original and new SKB. */
1196 tcp_set_skb_tso_segs(sk, skb, mss_now);
1197 tcp_set_skb_tso_segs(sk, buff, mss_now);
1199 /* If this packet has been sent out already, we must
1200 * adjust the various packet counters.
1202 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1203 int diff = old_factor - tcp_skb_pcount(skb) -
1204 tcp_skb_pcount(buff);
1207 tcp_adjust_pcount(sk, skb, diff);
1210 /* Link BUFF into the send queue. */
1211 __skb_header_release(buff);
1212 tcp_insert_write_queue_after(skb, buff, sk);
1217 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1218 * eventually). The difference is that pulled data not copied, but
1219 * immediately discarded.
1221 static void __pskb_trim_head(struct sk_buff *skb, int len)
1223 struct skb_shared_info *shinfo;
1226 eat = min_t(int, len, skb_headlen(skb));
1228 __skb_pull(skb, eat);
1235 shinfo = skb_shinfo(skb);
1236 for (i = 0; i < shinfo->nr_frags; i++) {
1237 int size = skb_frag_size(&shinfo->frags[i]);
1240 skb_frag_unref(skb, i);
1243 shinfo->frags[k] = shinfo->frags[i];
1245 shinfo->frags[k].page_offset += eat;
1246 skb_frag_size_sub(&shinfo->frags[k], eat);
1252 shinfo->nr_frags = k;
1254 skb_reset_tail_pointer(skb);
1255 skb->data_len -= len;
1256 skb->len = skb->data_len;
1259 /* Remove acked data from a packet in the transmit queue. */
1260 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1262 if (skb_unclone(skb, GFP_ATOMIC))
1265 __pskb_trim_head(skb, len);
1267 TCP_SKB_CB(skb)->seq += len;
1268 skb->ip_summed = CHECKSUM_PARTIAL;
1270 skb->truesize -= len;
1271 sk->sk_wmem_queued -= len;
1272 sk_mem_uncharge(sk, len);
1273 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1275 /* Any change of skb->len requires recalculation of tso factor. */
1276 if (tcp_skb_pcount(skb) > 1)
1277 tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
1282 /* Calculate MSS not accounting any TCP options. */
1283 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1285 const struct tcp_sock *tp = tcp_sk(sk);
1286 const struct inet_connection_sock *icsk = inet_csk(sk);
1289 /* Calculate base mss without TCP options:
1290 It is MMS_S - sizeof(tcphdr) of rfc1122
1292 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1294 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1295 if (icsk->icsk_af_ops->net_frag_header_len) {
1296 const struct dst_entry *dst = __sk_dst_get(sk);
1298 if (dst && dst_allfrag(dst))
1299 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1302 /* Clamp it (mss_clamp does not include tcp options) */
1303 if (mss_now > tp->rx_opt.mss_clamp)
1304 mss_now = tp->rx_opt.mss_clamp;
1306 /* Now subtract optional transport overhead */
1307 mss_now -= icsk->icsk_ext_hdr_len;
1309 /* Then reserve room for full set of TCP options and 8 bytes of data */
1315 /* Calculate MSS. Not accounting for SACKs here. */
1316 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1318 /* Subtract TCP options size, not including SACKs */
1319 return __tcp_mtu_to_mss(sk, pmtu) -
1320 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1323 /* Inverse of above */
1324 int tcp_mss_to_mtu(struct sock *sk, int mss)
1326 const struct tcp_sock *tp = tcp_sk(sk);
1327 const struct inet_connection_sock *icsk = inet_csk(sk);
1331 tp->tcp_header_len +
1332 icsk->icsk_ext_hdr_len +
1333 icsk->icsk_af_ops->net_header_len;
1335 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1336 if (icsk->icsk_af_ops->net_frag_header_len) {
1337 const struct dst_entry *dst = __sk_dst_get(sk);
1339 if (dst && dst_allfrag(dst))
1340 mtu += icsk->icsk_af_ops->net_frag_header_len;
1345 /* MTU probing init per socket */
1346 void tcp_mtup_init(struct sock *sk)
1348 struct tcp_sock *tp = tcp_sk(sk);
1349 struct inet_connection_sock *icsk = inet_csk(sk);
1350 struct net *net = sock_net(sk);
1352 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1353 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1354 icsk->icsk_af_ops->net_header_len;
1355 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1356 icsk->icsk_mtup.probe_size = 0;
1358 EXPORT_SYMBOL(tcp_mtup_init);
1360 /* This function synchronize snd mss to current pmtu/exthdr set.
1362 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1363 for TCP options, but includes only bare TCP header.
1365 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1366 It is minimum of user_mss and mss received with SYN.
1367 It also does not include TCP options.
1369 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1371 tp->mss_cache is current effective sending mss, including
1372 all tcp options except for SACKs. It is evaluated,
1373 taking into account current pmtu, but never exceeds
1374 tp->rx_opt.mss_clamp.
1376 NOTE1. rfc1122 clearly states that advertised MSS
1377 DOES NOT include either tcp or ip options.
1379 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1380 are READ ONLY outside this function. --ANK (980731)
1382 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1384 struct tcp_sock *tp = tcp_sk(sk);
1385 struct inet_connection_sock *icsk = inet_csk(sk);
1388 if (icsk->icsk_mtup.search_high > pmtu)
1389 icsk->icsk_mtup.search_high = pmtu;
1391 mss_now = tcp_mtu_to_mss(sk, pmtu);
1392 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1394 /* And store cached results */
1395 icsk->icsk_pmtu_cookie = pmtu;
1396 if (icsk->icsk_mtup.enabled)
1397 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1398 tp->mss_cache = mss_now;
1402 EXPORT_SYMBOL(tcp_sync_mss);
1404 /* Compute the current effective MSS, taking SACKs and IP options,
1405 * and even PMTU discovery events into account.
1407 unsigned int tcp_current_mss(struct sock *sk)
1409 const struct tcp_sock *tp = tcp_sk(sk);
1410 const struct dst_entry *dst = __sk_dst_get(sk);
1412 unsigned int header_len;
1413 struct tcp_out_options opts;
1414 struct tcp_md5sig_key *md5;
1416 mss_now = tp->mss_cache;
1419 u32 mtu = dst_mtu(dst);
1420 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1421 mss_now = tcp_sync_mss(sk, mtu);
1424 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1425 sizeof(struct tcphdr);
1426 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1427 * some common options. If this is an odd packet (because we have SACK
1428 * blocks etc) then our calculated header_len will be different, and
1429 * we have to adjust mss_now correspondingly */
1430 if (header_len != tp->tcp_header_len) {
1431 int delta = (int) header_len - tp->tcp_header_len;
1438 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1439 * As additional protections, we do not touch cwnd in retransmission phases,
1440 * and if application hit its sndbuf limit recently.
1442 static void tcp_cwnd_application_limited(struct sock *sk)
1444 struct tcp_sock *tp = tcp_sk(sk);
1446 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1447 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1448 /* Limited by application or receiver window. */
1449 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1450 u32 win_used = max(tp->snd_cwnd_used, init_win);
1451 if (win_used < tp->snd_cwnd) {
1452 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1453 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1455 tp->snd_cwnd_used = 0;
1457 tp->snd_cwnd_stamp = tcp_time_stamp;
1460 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1462 struct tcp_sock *tp = tcp_sk(sk);
1464 /* Track the maximum number of outstanding packets in each
1465 * window, and remember whether we were cwnd-limited then.
1467 if (!before(tp->snd_una, tp->max_packets_seq) ||
1468 tp->packets_out > tp->max_packets_out) {
1469 tp->max_packets_out = tp->packets_out;
1470 tp->max_packets_seq = tp->snd_nxt;
1471 tp->is_cwnd_limited = is_cwnd_limited;
1474 if (tcp_is_cwnd_limited(sk)) {
1475 /* Network is feed fully. */
1476 tp->snd_cwnd_used = 0;
1477 tp->snd_cwnd_stamp = tcp_time_stamp;
1479 /* Network starves. */
1480 if (tp->packets_out > tp->snd_cwnd_used)
1481 tp->snd_cwnd_used = tp->packets_out;
1483 if (sysctl_tcp_slow_start_after_idle &&
1484 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1485 tcp_cwnd_application_limited(sk);
1489 /* Minshall's variant of the Nagle send check. */
1490 static bool tcp_minshall_check(const struct tcp_sock *tp)
1492 return after(tp->snd_sml, tp->snd_una) &&
1493 !after(tp->snd_sml, tp->snd_nxt);
1496 /* Update snd_sml if this skb is under mss
1497 * Note that a TSO packet might end with a sub-mss segment
1498 * The test is really :
1499 * if ((skb->len % mss) != 0)
1500 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1501 * But we can avoid doing the divide again given we already have
1502 * skb_pcount = skb->len / mss_now
1504 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1505 const struct sk_buff *skb)
1507 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1508 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1511 /* Return false, if packet can be sent now without violation Nagle's rules:
1512 * 1. It is full sized. (provided by caller in %partial bool)
1513 * 2. Or it contains FIN. (already checked by caller)
1514 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1515 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1516 * With Minshall's modification: all sent small packets are ACKed.
1518 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1522 ((nonagle & TCP_NAGLE_CORK) ||
1523 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1526 /* Return how many segs we'd like on a TSO packet,
1527 * to send one TSO packet per ms
1529 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1533 bytes = min(sk->sk_pacing_rate >> 10,
1534 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1536 /* Goal is to send at least one packet per ms,
1537 * not one big TSO packet every 100 ms.
1538 * This preserves ACK clocking and is consistent
1539 * with tcp_tso_should_defer() heuristic.
1541 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1543 return min_t(u32, segs, sk->sk_gso_max_segs);
1546 /* Returns the portion of skb which can be sent right away */
1547 static unsigned int tcp_mss_split_point(const struct sock *sk,
1548 const struct sk_buff *skb,
1549 unsigned int mss_now,
1550 unsigned int max_segs,
1553 const struct tcp_sock *tp = tcp_sk(sk);
1554 u32 partial, needed, window, max_len;
1556 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1557 max_len = mss_now * max_segs;
1559 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1562 needed = min(skb->len, window);
1564 if (max_len <= needed)
1567 partial = needed % mss_now;
1568 /* If last segment is not a full MSS, check if Nagle rules allow us
1569 * to include this last segment in this skb.
1570 * Otherwise, we'll split the skb at last MSS boundary
1572 if (tcp_nagle_check(partial != 0, tp, nonagle))
1573 return needed - partial;
1578 /* Can at least one segment of SKB be sent right now, according to the
1579 * congestion window rules? If so, return how many segments are allowed.
1581 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1582 const struct sk_buff *skb)
1584 u32 in_flight, cwnd, halfcwnd;
1586 /* Don't be strict about the congestion window for the final FIN. */
1587 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1588 tcp_skb_pcount(skb) == 1)
1591 in_flight = tcp_packets_in_flight(tp);
1592 cwnd = tp->snd_cwnd;
1593 if (in_flight >= cwnd)
1596 /* For better scheduling, ensure we have at least
1597 * 2 GSO packets in flight.
1599 halfcwnd = max(cwnd >> 1, 1U);
1600 return min(halfcwnd, cwnd - in_flight);
1603 /* Initialize TSO state of a skb.
1604 * This must be invoked the first time we consider transmitting
1605 * SKB onto the wire.
1607 static int tcp_init_tso_segs(const struct sock *sk, struct sk_buff *skb,
1608 unsigned int mss_now)
1610 int tso_segs = tcp_skb_pcount(skb);
1612 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1613 tcp_set_skb_tso_segs(sk, skb, mss_now);
1614 tso_segs = tcp_skb_pcount(skb);
1620 /* Return true if the Nagle test allows this packet to be
1623 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1624 unsigned int cur_mss, int nonagle)
1626 /* Nagle rule does not apply to frames, which sit in the middle of the
1627 * write_queue (they have no chances to get new data).
1629 * This is implemented in the callers, where they modify the 'nonagle'
1630 * argument based upon the location of SKB in the send queue.
1632 if (nonagle & TCP_NAGLE_PUSH)
1635 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1636 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1639 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1645 /* Does at least the first segment of SKB fit into the send window? */
1646 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1647 const struct sk_buff *skb,
1648 unsigned int cur_mss)
1650 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1652 if (skb->len > cur_mss)
1653 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1655 return !after(end_seq, tcp_wnd_end(tp));
1658 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1659 * should be put on the wire right now. If so, it returns the number of
1660 * packets allowed by the congestion window.
1662 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1663 unsigned int cur_mss, int nonagle)
1665 const struct tcp_sock *tp = tcp_sk(sk);
1666 unsigned int cwnd_quota;
1668 tcp_init_tso_segs(sk, skb, cur_mss);
1670 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1673 cwnd_quota = tcp_cwnd_test(tp, skb);
1674 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1680 /* Test if sending is allowed right now. */
1681 bool tcp_may_send_now(struct sock *sk)
1683 const struct tcp_sock *tp = tcp_sk(sk);
1684 struct sk_buff *skb = tcp_send_head(sk);
1687 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1688 (tcp_skb_is_last(sk, skb) ?
1689 tp->nonagle : TCP_NAGLE_PUSH));
1692 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1693 * which is put after SKB on the list. It is very much like
1694 * tcp_fragment() except that it may make several kinds of assumptions
1695 * in order to speed up the splitting operation. In particular, we
1696 * know that all the data is in scatter-gather pages, and that the
1697 * packet has never been sent out before (and thus is not cloned).
1699 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1700 unsigned int mss_now, gfp_t gfp)
1702 struct sk_buff *buff;
1703 int nlen = skb->len - len;
1706 /* All of a TSO frame must be composed of paged data. */
1707 if (skb->len != skb->data_len)
1708 return tcp_fragment(sk, skb, len, mss_now, gfp);
1710 buff = sk_stream_alloc_skb(sk, 0, gfp);
1711 if (unlikely(buff == NULL))
1714 sk->sk_wmem_queued += buff->truesize;
1715 sk_mem_charge(sk, buff->truesize);
1716 buff->truesize += nlen;
1717 skb->truesize -= nlen;
1719 /* Correct the sequence numbers. */
1720 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1721 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1722 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1724 /* PSH and FIN should only be set in the second packet. */
1725 flags = TCP_SKB_CB(skb)->tcp_flags;
1726 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1727 TCP_SKB_CB(buff)->tcp_flags = flags;
1729 /* This packet was never sent out yet, so no SACK bits. */
1730 TCP_SKB_CB(buff)->sacked = 0;
1732 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1733 skb_split(skb, buff, len);
1734 tcp_fragment_tstamp(skb, buff);
1736 /* Fix up tso_factor for both original and new SKB. */
1737 tcp_set_skb_tso_segs(sk, skb, mss_now);
1738 tcp_set_skb_tso_segs(sk, buff, mss_now);
1740 /* Link BUFF into the send queue. */
1741 __skb_header_release(buff);
1742 tcp_insert_write_queue_after(skb, buff, sk);
1747 /* Try to defer sending, if possible, in order to minimize the amount
1748 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1750 * This algorithm is from John Heffner.
1752 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1753 bool *is_cwnd_limited, u32 max_segs)
1755 const struct inet_connection_sock *icsk = inet_csk(sk);
1756 u32 age, send_win, cong_win, limit, in_flight;
1757 struct tcp_sock *tp = tcp_sk(sk);
1758 struct skb_mstamp now;
1759 struct sk_buff *head;
1762 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1765 if (icsk->icsk_ca_state != TCP_CA_Open)
1768 /* Avoid bursty behavior by allowing defer
1769 * only if the last write was recent.
1771 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1774 in_flight = tcp_packets_in_flight(tp);
1776 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1778 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1780 /* From in_flight test above, we know that cwnd > in_flight. */
1781 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1783 limit = min(send_win, cong_win);
1785 /* If a full-sized TSO skb can be sent, do it. */
1786 if (limit >= max_segs * tp->mss_cache)
1789 /* Middle in queue won't get any more data, full sendable already? */
1790 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1793 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1795 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1797 /* If at least some fraction of a window is available,
1800 chunk /= win_divisor;
1804 /* Different approach, try not to defer past a single
1805 * ACK. Receiver should ACK every other full sized
1806 * frame, so if we have space for more than 3 frames
1809 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1813 head = tcp_write_queue_head(sk);
1814 skb_mstamp_get(&now);
1815 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1816 /* If next ACK is likely to come too late (half srtt), do not defer */
1817 if (age < (tp->srtt_us >> 4))
1820 /* Ok, it looks like it is advisable to defer. */
1822 if (cong_win < send_win && cong_win < skb->len)
1823 *is_cwnd_limited = true;
1831 /* Create a new MTU probe if we are ready.
1832 * MTU probe is regularly attempting to increase the path MTU by
1833 * deliberately sending larger packets. This discovers routing
1834 * changes resulting in larger path MTUs.
1836 * Returns 0 if we should wait to probe (no cwnd available),
1837 * 1 if a probe was sent,
1840 static int tcp_mtu_probe(struct sock *sk)
1842 struct tcp_sock *tp = tcp_sk(sk);
1843 struct inet_connection_sock *icsk = inet_csk(sk);
1844 struct sk_buff *skb, *nskb, *next;
1851 /* Not currently probing/verifying,
1853 * have enough cwnd, and
1854 * not SACKing (the variable headers throw things off) */
1855 if (!icsk->icsk_mtup.enabled ||
1856 icsk->icsk_mtup.probe_size ||
1857 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1858 tp->snd_cwnd < 11 ||
1859 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1862 /* Very simple search strategy: just double the MSS. */
1863 mss_now = tcp_current_mss(sk);
1864 probe_size = 2 * tp->mss_cache;
1865 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1866 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) {
1867 /* TODO: set timer for probe_converge_event */
1871 /* Have enough data in the send queue to probe? */
1872 if (tp->write_seq - tp->snd_nxt < size_needed)
1875 if (tp->snd_wnd < size_needed)
1877 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1880 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1881 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1882 if (!tcp_packets_in_flight(tp))
1888 /* We're allowed to probe. Build it now. */
1889 if ((nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC)) == NULL)
1891 sk->sk_wmem_queued += nskb->truesize;
1892 sk_mem_charge(sk, nskb->truesize);
1894 skb = tcp_send_head(sk);
1896 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1897 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1898 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1899 TCP_SKB_CB(nskb)->sacked = 0;
1901 nskb->ip_summed = skb->ip_summed;
1903 tcp_insert_write_queue_before(nskb, skb, sk);
1906 tcp_for_write_queue_from_safe(skb, next, sk) {
1907 copy = min_t(int, skb->len, probe_size - len);
1908 if (nskb->ip_summed)
1909 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1911 nskb->csum = skb_copy_and_csum_bits(skb, 0,
1912 skb_put(nskb, copy),
1915 if (skb->len <= copy) {
1916 /* We've eaten all the data from this skb.
1918 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
1919 tcp_unlink_write_queue(skb, sk);
1920 sk_wmem_free_skb(sk, skb);
1922 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
1923 ~(TCPHDR_FIN|TCPHDR_PSH);
1924 if (!skb_shinfo(skb)->nr_frags) {
1925 skb_pull(skb, copy);
1926 if (skb->ip_summed != CHECKSUM_PARTIAL)
1927 skb->csum = csum_partial(skb->data,
1930 __pskb_trim_head(skb, copy);
1931 tcp_set_skb_tso_segs(sk, skb, mss_now);
1933 TCP_SKB_CB(skb)->seq += copy;
1938 if (len >= probe_size)
1941 tcp_init_tso_segs(sk, nskb, nskb->len);
1943 /* We're ready to send. If this fails, the probe will
1944 * be resegmented into mss-sized pieces by tcp_write_xmit().
1946 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
1947 /* Decrement cwnd here because we are sending
1948 * effectively two packets. */
1950 tcp_event_new_data_sent(sk, nskb);
1952 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
1953 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
1954 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
1962 /* This routine writes packets to the network. It advances the
1963 * send_head. This happens as incoming acks open up the remote
1966 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
1967 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
1968 * account rare use of URG, this is not a big flaw.
1970 * Send at most one packet when push_one > 0. Temporarily ignore
1971 * cwnd limit to force at most one packet out when push_one == 2.
1973 * Returns true, if no segments are in flight and we have queued segments,
1974 * but cannot send anything now because of SWS or another problem.
1976 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
1977 int push_one, gfp_t gfp)
1979 struct tcp_sock *tp = tcp_sk(sk);
1980 struct sk_buff *skb;
1981 unsigned int tso_segs, sent_pkts;
1984 bool is_cwnd_limited = false;
1990 /* Do MTU probing. */
1991 result = tcp_mtu_probe(sk);
1994 } else if (result > 0) {
1999 max_segs = tcp_tso_autosize(sk, mss_now);
2000 while ((skb = tcp_send_head(sk))) {
2003 tso_segs = tcp_init_tso_segs(sk, skb, mss_now);
2006 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2007 /* "skb_mstamp" is used as a start point for the retransmit timer */
2008 skb_mstamp_get(&skb->skb_mstamp);
2009 goto repair; /* Skip network transmission */
2012 cwnd_quota = tcp_cwnd_test(tp, skb);
2014 is_cwnd_limited = true;
2016 /* Force out a loss probe pkt. */
2022 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2025 if (tso_segs == 1 || !max_segs) {
2026 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2027 (tcp_skb_is_last(sk, skb) ?
2028 nonagle : TCP_NAGLE_PUSH))))
2032 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2038 if (tso_segs > 1 && max_segs && !tcp_urg_mode(tp))
2039 limit = tcp_mss_split_point(sk, skb, mss_now,
2045 if (skb->len > limit &&
2046 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2049 /* TCP Small Queues :
2050 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2052 * - better RTT estimation and ACK scheduling
2055 * Alas, some drivers / subsystems require a fair amount
2056 * of queued bytes to ensure line rate.
2057 * One example is wifi aggregation (802.11 AMPDU)
2059 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2060 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2062 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2063 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2064 /* It is possible TX completion already happened
2065 * before we set TSQ_THROTTLED, so we must
2066 * test again the condition.
2068 smp_mb__after_atomic();
2069 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2073 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2077 /* Advance the send_head. This one is sent out.
2078 * This call will increment packets_out.
2080 tcp_event_new_data_sent(sk, skb);
2082 tcp_minshall_update(tp, mss_now, skb);
2083 sent_pkts += tcp_skb_pcount(skb);
2089 if (likely(sent_pkts)) {
2090 if (tcp_in_cwnd_reduction(sk))
2091 tp->prr_out += sent_pkts;
2093 /* Send one loss probe per tail loss episode. */
2095 tcp_schedule_loss_probe(sk);
2096 tcp_cwnd_validate(sk, is_cwnd_limited);
2099 return (push_one == 2) || (!tp->packets_out && tcp_send_head(sk));
2102 bool tcp_schedule_loss_probe(struct sock *sk)
2104 struct inet_connection_sock *icsk = inet_csk(sk);
2105 struct tcp_sock *tp = tcp_sk(sk);
2106 u32 timeout, tlp_time_stamp, rto_time_stamp;
2107 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2109 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2111 /* No consecutive loss probes. */
2112 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2116 /* Don't do any loss probe on a Fast Open connection before 3WHS
2119 if (sk->sk_state == TCP_SYN_RECV)
2122 /* TLP is only scheduled when next timer event is RTO. */
2123 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2126 /* Schedule a loss probe in 2*RTT for SACK capable connections
2127 * in Open state, that are either limited by cwnd or application.
2129 if (sysctl_tcp_early_retrans < 3 || !tp->srtt_us || !tp->packets_out ||
2130 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2133 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2137 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2138 * for delayed ack when there's one outstanding packet.
2141 if (tp->packets_out == 1)
2142 timeout = max_t(u32, timeout,
2143 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2144 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2146 /* If RTO is shorter, just schedule TLP in its place. */
2147 tlp_time_stamp = tcp_time_stamp + timeout;
2148 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2149 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2150 s32 delta = rto_time_stamp - tcp_time_stamp;
2155 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2160 /* Thanks to skb fast clones, we can detect if a prior transmit of
2161 * a packet is still in a qdisc or driver queue.
2162 * In this case, there is very little point doing a retransmit !
2163 * Note: This is called from BH context only.
2165 static bool skb_still_in_host_queue(const struct sock *sk,
2166 const struct sk_buff *skb)
2168 if (unlikely(skb_fclone_busy(sk, skb))) {
2169 NET_INC_STATS_BH(sock_net(sk),
2170 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2176 /* When probe timeout (PTO) fires, send a new segment if one exists, else
2177 * retransmit the last segment.
2179 void tcp_send_loss_probe(struct sock *sk)
2181 struct tcp_sock *tp = tcp_sk(sk);
2182 struct sk_buff *skb;
2184 int mss = tcp_current_mss(sk);
2187 if (tcp_send_head(sk) != NULL) {
2188 err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2192 /* At most one outstanding TLP retransmission. */
2193 if (tp->tlp_high_seq)
2196 /* Retransmit last segment. */
2197 skb = tcp_write_queue_tail(sk);
2201 if (skb_still_in_host_queue(sk, skb))
2204 pcount = tcp_skb_pcount(skb);
2205 if (WARN_ON(!pcount))
2208 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2209 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2212 skb = tcp_write_queue_tail(sk);
2215 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2218 err = __tcp_retransmit_skb(sk, skb);
2220 /* Record snd_nxt for loss detection. */
2222 tp->tlp_high_seq = tp->snd_nxt;
2225 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2226 inet_csk(sk)->icsk_rto,
2230 NET_INC_STATS_BH(sock_net(sk),
2231 LINUX_MIB_TCPLOSSPROBES);
2234 /* Push out any pending frames which were held back due to
2235 * TCP_CORK or attempt at coalescing tiny packets.
2236 * The socket must be locked by the caller.
2238 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2241 /* If we are closed, the bytes will have to remain here.
2242 * In time closedown will finish, we empty the write queue and
2243 * all will be happy.
2245 if (unlikely(sk->sk_state == TCP_CLOSE))
2248 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2249 sk_gfp_atomic(sk, GFP_ATOMIC)))
2250 tcp_check_probe_timer(sk);
2253 /* Send _single_ skb sitting at the send head. This function requires
2254 * true push pending frames to setup probe timer etc.
2256 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2258 struct sk_buff *skb = tcp_send_head(sk);
2260 BUG_ON(!skb || skb->len < mss_now);
2262 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2265 /* This function returns the amount that we can raise the
2266 * usable window based on the following constraints
2268 * 1. The window can never be shrunk once it is offered (RFC 793)
2269 * 2. We limit memory per socket
2272 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2273 * RECV.NEXT + RCV.WIN fixed until:
2274 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2276 * i.e. don't raise the right edge of the window until you can raise
2277 * it at least MSS bytes.
2279 * Unfortunately, the recommended algorithm breaks header prediction,
2280 * since header prediction assumes th->window stays fixed.
2282 * Strictly speaking, keeping th->window fixed violates the receiver
2283 * side SWS prevention criteria. The problem is that under this rule
2284 * a stream of single byte packets will cause the right side of the
2285 * window to always advance by a single byte.
2287 * Of course, if the sender implements sender side SWS prevention
2288 * then this will not be a problem.
2290 * BSD seems to make the following compromise:
2292 * If the free space is less than the 1/4 of the maximum
2293 * space available and the free space is less than 1/2 mss,
2294 * then set the window to 0.
2295 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2296 * Otherwise, just prevent the window from shrinking
2297 * and from being larger than the largest representable value.
2299 * This prevents incremental opening of the window in the regime
2300 * where TCP is limited by the speed of the reader side taking
2301 * data out of the TCP receive queue. It does nothing about
2302 * those cases where the window is constrained on the sender side
2303 * because the pipeline is full.
2305 * BSD also seems to "accidentally" limit itself to windows that are a
2306 * multiple of MSS, at least until the free space gets quite small.
2307 * This would appear to be a side effect of the mbuf implementation.
2308 * Combining these two algorithms results in the observed behavior
2309 * of having a fixed window size at almost all times.
2311 * Below we obtain similar behavior by forcing the offered window to
2312 * a multiple of the mss when it is feasible to do so.
2314 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2315 * Regular options like TIMESTAMP are taken into account.
2317 u32 __tcp_select_window(struct sock *sk)
2319 struct inet_connection_sock *icsk = inet_csk(sk);
2320 struct tcp_sock *tp = tcp_sk(sk);
2321 /* MSS for the peer's data. Previous versions used mss_clamp
2322 * here. I don't know if the value based on our guesses
2323 * of peer's MSS is better for the performance. It's more correct
2324 * but may be worse for the performance because of rcv_mss
2325 * fluctuations. --SAW 1998/11/1
2327 int mss = icsk->icsk_ack.rcv_mss;
2328 int free_space = tcp_space(sk);
2329 int allowed_space = tcp_full_space(sk);
2330 int full_space = min_t(int, tp->window_clamp, allowed_space);
2333 if (mss > full_space)
2336 if (free_space < (full_space >> 1)) {
2337 icsk->icsk_ack.quick = 0;
2339 if (sk_under_memory_pressure(sk))
2340 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2343 /* free_space might become our new window, make sure we don't
2344 * increase it due to wscale.
2346 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2348 /* if free space is less than mss estimate, or is below 1/16th
2349 * of the maximum allowed, try to move to zero-window, else
2350 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2351 * new incoming data is dropped due to memory limits.
2352 * With large window, mss test triggers way too late in order
2353 * to announce zero window in time before rmem limit kicks in.
2355 if (free_space < (allowed_space >> 4) || free_space < mss)
2359 if (free_space > tp->rcv_ssthresh)
2360 free_space = tp->rcv_ssthresh;
2362 /* Don't do rounding if we are using window scaling, since the
2363 * scaled window will not line up with the MSS boundary anyway.
2365 window = tp->rcv_wnd;
2366 if (tp->rx_opt.rcv_wscale) {
2367 window = free_space;
2369 /* Advertise enough space so that it won't get scaled away.
2370 * Import case: prevent zero window announcement if
2371 * 1<<rcv_wscale > mss.
2373 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2374 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2375 << tp->rx_opt.rcv_wscale);
2377 /* Get the largest window that is a nice multiple of mss.
2378 * Window clamp already applied above.
2379 * If our current window offering is within 1 mss of the
2380 * free space we just keep it. This prevents the divide
2381 * and multiply from happening most of the time.
2382 * We also don't do any window rounding when the free space
2385 if (window <= free_space - mss || window > free_space)
2386 window = (free_space / mss) * mss;
2387 else if (mss == full_space &&
2388 free_space > window + (full_space >> 1))
2389 window = free_space;
2395 /* Collapses two adjacent SKB's during retransmission. */
2396 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2398 struct tcp_sock *tp = tcp_sk(sk);
2399 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2400 int skb_size, next_skb_size;
2402 skb_size = skb->len;
2403 next_skb_size = next_skb->len;
2405 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2407 tcp_highest_sack_combine(sk, next_skb, skb);
2409 tcp_unlink_write_queue(next_skb, sk);
2411 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2414 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2415 skb->ip_summed = CHECKSUM_PARTIAL;
2417 if (skb->ip_summed != CHECKSUM_PARTIAL)
2418 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2420 /* Update sequence range on original skb. */
2421 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2423 /* Merge over control information. This moves PSH/FIN etc. over */
2424 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2426 /* All done, get rid of second SKB and account for it so
2427 * packet counting does not break.
2429 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2431 /* changed transmit queue under us so clear hints */
2432 tcp_clear_retrans_hints_partial(tp);
2433 if (next_skb == tp->retransmit_skb_hint)
2434 tp->retransmit_skb_hint = skb;
2436 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2438 sk_wmem_free_skb(sk, next_skb);
2441 /* Check if coalescing SKBs is legal. */
2442 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2444 if (tcp_skb_pcount(skb) > 1)
2446 /* TODO: SACK collapsing could be used to remove this condition */
2447 if (skb_shinfo(skb)->nr_frags != 0)
2449 if (skb_cloned(skb))
2451 if (skb == tcp_send_head(sk))
2453 /* Some heurestics for collapsing over SACK'd could be invented */
2454 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2460 /* Collapse packets in the retransmit queue to make to create
2461 * less packets on the wire. This is only done on retransmission.
2463 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2466 struct tcp_sock *tp = tcp_sk(sk);
2467 struct sk_buff *skb = to, *tmp;
2470 if (!sysctl_tcp_retrans_collapse)
2472 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2475 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2476 if (!tcp_can_collapse(sk, skb))
2488 /* Punt if not enough space exists in the first SKB for
2489 * the data in the second
2491 if (skb->len > skb_availroom(to))
2494 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2497 tcp_collapse_retrans(sk, to);
2501 /* This retransmits one SKB. Policy decisions and retransmit queue
2502 * state updates are done by the caller. Returns non-zero if an
2503 * error occurred which prevented the send.
2505 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2507 struct tcp_sock *tp = tcp_sk(sk);
2508 struct inet_connection_sock *icsk = inet_csk(sk);
2509 unsigned int cur_mss;
2512 /* Inconslusive MTU probe */
2513 if (icsk->icsk_mtup.probe_size) {
2514 icsk->icsk_mtup.probe_size = 0;
2517 /* Do not sent more than we queued. 1/4 is reserved for possible
2518 * copying overhead: fragmentation, tunneling, mangling etc.
2520 if (atomic_read(&sk->sk_wmem_alloc) >
2521 min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
2524 if (skb_still_in_host_queue(sk, skb))
2527 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2528 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
2530 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2534 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2535 return -EHOSTUNREACH; /* Routing failure or similar. */
2537 cur_mss = tcp_current_mss(sk);
2539 /* If receiver has shrunk his window, and skb is out of
2540 * new window, do not retransmit it. The exception is the
2541 * case, when window is shrunk to zero. In this case
2542 * our retransmit serves as a zero window probe.
2544 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2545 TCP_SKB_CB(skb)->seq != tp->snd_una)
2548 if (skb->len > cur_mss) {
2549 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2550 return -ENOMEM; /* We'll try again later. */
2552 int oldpcount = tcp_skb_pcount(skb);
2554 if (unlikely(oldpcount > 1)) {
2555 if (skb_unclone(skb, GFP_ATOMIC))
2557 tcp_init_tso_segs(sk, skb, cur_mss);
2558 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2562 tcp_retrans_try_collapse(sk, skb, cur_mss);
2564 /* Make a copy, if the first transmission SKB clone we made
2565 * is still in somebody's hands, else make a clone.
2568 /* make sure skb->data is aligned on arches that require it
2569 * and check if ack-trimming & collapsing extended the headroom
2570 * beyond what csum_start can cover.
2572 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2573 skb_headroom(skb) >= 0xFFFF)) {
2574 struct sk_buff *nskb = __pskb_copy(skb, MAX_TCP_HEADER,
2576 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2579 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2583 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2584 /* Update global TCP statistics. */
2585 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2586 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2587 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2588 tp->total_retrans++;
2593 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2595 struct tcp_sock *tp = tcp_sk(sk);
2596 int err = __tcp_retransmit_skb(sk, skb);
2599 #if FASTRETRANS_DEBUG > 0
2600 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2601 net_dbg_ratelimited("retrans_out leaked\n");
2604 if (!tp->retrans_out)
2605 tp->lost_retrans_low = tp->snd_nxt;
2606 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2607 tp->retrans_out += tcp_skb_pcount(skb);
2609 /* Save stamp of the first retransmit. */
2610 if (!tp->retrans_stamp)
2611 tp->retrans_stamp = tcp_skb_timestamp(skb);
2613 /* snd_nxt is stored to detect loss of retransmitted segment,
2614 * see tcp_input.c tcp_sacktag_write_queue().
2616 TCP_SKB_CB(skb)->ack_seq = tp->snd_nxt;
2617 } else if (err != -EBUSY) {
2618 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2621 if (tp->undo_retrans < 0)
2622 tp->undo_retrans = 0;
2623 tp->undo_retrans += tcp_skb_pcount(skb);
2627 /* Check if we forward retransmits are possible in the current
2628 * window/congestion state.
2630 static bool tcp_can_forward_retransmit(struct sock *sk)
2632 const struct inet_connection_sock *icsk = inet_csk(sk);
2633 const struct tcp_sock *tp = tcp_sk(sk);
2635 /* Forward retransmissions are possible only during Recovery. */
2636 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2639 /* No forward retransmissions in Reno are possible. */
2640 if (tcp_is_reno(tp))
2643 /* Yeah, we have to make difficult choice between forward transmission
2644 * and retransmission... Both ways have their merits...
2646 * For now we do not retransmit anything, while we have some new
2647 * segments to send. In the other cases, follow rule 3 for
2648 * NextSeg() specified in RFC3517.
2651 if (tcp_may_send_now(sk))
2657 /* This gets called after a retransmit timeout, and the initially
2658 * retransmitted data is acknowledged. It tries to continue
2659 * resending the rest of the retransmit queue, until either
2660 * we've sent it all or the congestion window limit is reached.
2661 * If doing SACK, the first ACK which comes back for a timeout
2662 * based retransmit packet might feed us FACK information again.
2663 * If so, we use it to avoid unnecessarily retransmissions.
2665 void tcp_xmit_retransmit_queue(struct sock *sk)
2667 const struct inet_connection_sock *icsk = inet_csk(sk);
2668 struct tcp_sock *tp = tcp_sk(sk);
2669 struct sk_buff *skb;
2670 struct sk_buff *hole = NULL;
2673 int fwd_rexmitting = 0;
2675 if (!tp->packets_out)
2679 tp->retransmit_high = tp->snd_una;
2681 if (tp->retransmit_skb_hint) {
2682 skb = tp->retransmit_skb_hint;
2683 last_lost = TCP_SKB_CB(skb)->end_seq;
2684 if (after(last_lost, tp->retransmit_high))
2685 last_lost = tp->retransmit_high;
2687 skb = tcp_write_queue_head(sk);
2688 last_lost = tp->snd_una;
2691 tcp_for_write_queue_from(skb, sk) {
2692 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2694 if (skb == tcp_send_head(sk))
2696 /* we could do better than to assign each time */
2698 tp->retransmit_skb_hint = skb;
2700 /* Assume this retransmit will generate
2701 * only one packet for congestion window
2702 * calculation purposes. This works because
2703 * tcp_retransmit_skb() will chop up the
2704 * packet to be MSS sized and all the
2705 * packet counting works out.
2707 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2710 if (fwd_rexmitting) {
2712 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2714 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2716 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2717 tp->retransmit_high = last_lost;
2718 if (!tcp_can_forward_retransmit(sk))
2720 /* Backtrack if necessary to non-L'ed skb */
2728 } else if (!(sacked & TCPCB_LOST)) {
2729 if (hole == NULL && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2734 last_lost = TCP_SKB_CB(skb)->end_seq;
2735 if (icsk->icsk_ca_state != TCP_CA_Loss)
2736 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2738 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2741 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2744 if (tcp_retransmit_skb(sk, skb))
2747 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2749 if (tcp_in_cwnd_reduction(sk))
2750 tp->prr_out += tcp_skb_pcount(skb);
2752 if (skb == tcp_write_queue_head(sk))
2753 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2754 inet_csk(sk)->icsk_rto,
2759 /* Send a fin. The caller locks the socket for us. This cannot be
2760 * allowed to fail queueing a FIN frame under any circumstances.
2762 void tcp_send_fin(struct sock *sk)
2764 struct tcp_sock *tp = tcp_sk(sk);
2765 struct sk_buff *skb = tcp_write_queue_tail(sk);
2768 /* Optimization, tack on the FIN if we have a queue of
2769 * unsent frames. But be careful about outgoing SACKS
2772 mss_now = tcp_current_mss(sk);
2774 if (tcp_send_head(sk) != NULL) {
2775 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_FIN;
2776 TCP_SKB_CB(skb)->end_seq++;
2779 /* Socket is locked, keep trying until memory is available. */
2781 skb = alloc_skb_fclone(MAX_TCP_HEADER,
2788 /* Reserve space for headers and prepare control bits. */
2789 skb_reserve(skb, MAX_TCP_HEADER);
2790 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2791 tcp_init_nondata_skb(skb, tp->write_seq,
2792 TCPHDR_ACK | TCPHDR_FIN);
2793 tcp_queue_skb(sk, skb);
2795 __tcp_push_pending_frames(sk, mss_now, TCP_NAGLE_OFF);
2798 /* We get here when a process closes a file descriptor (either due to
2799 * an explicit close() or as a byproduct of exit()'ing) and there
2800 * was unread data in the receive queue. This behavior is recommended
2801 * by RFC 2525, section 2.17. -DaveM
2803 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2805 struct sk_buff *skb;
2807 /* NOTE: No TCP options attached and we never retransmit this. */
2808 skb = alloc_skb(MAX_TCP_HEADER, priority);
2810 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2814 /* Reserve space for headers and prepare control bits. */
2815 skb_reserve(skb, MAX_TCP_HEADER);
2816 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2817 TCPHDR_ACK | TCPHDR_RST);
2819 if (tcp_transmit_skb(sk, skb, 0, priority))
2820 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2822 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2825 /* Send a crossed SYN-ACK during socket establishment.
2826 * WARNING: This routine must only be called when we have already sent
2827 * a SYN packet that crossed the incoming SYN that caused this routine
2828 * to get called. If this assumption fails then the initial rcv_wnd
2829 * and rcv_wscale values will not be correct.
2831 int tcp_send_synack(struct sock *sk)
2833 struct sk_buff *skb;
2835 skb = tcp_write_queue_head(sk);
2836 if (skb == NULL || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2837 pr_debug("%s: wrong queue state\n", __func__);
2840 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2841 if (skb_cloned(skb)) {
2842 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2845 tcp_unlink_write_queue(skb, sk);
2846 __skb_header_release(nskb);
2847 __tcp_add_write_queue_head(sk, nskb);
2848 sk_wmem_free_skb(sk, skb);
2849 sk->sk_wmem_queued += nskb->truesize;
2850 sk_mem_charge(sk, nskb->truesize);
2854 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2855 tcp_ecn_send_synack(sk, skb);
2857 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2861 * tcp_make_synack - Prepare a SYN-ACK.
2862 * sk: listener socket
2863 * dst: dst entry attached to the SYNACK
2864 * req: request_sock pointer
2866 * Allocate one skb and build a SYNACK packet.
2867 * @dst is consumed : Caller should not use it again.
2869 struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
2870 struct request_sock *req,
2871 struct tcp_fastopen_cookie *foc)
2873 struct tcp_out_options opts;
2874 struct inet_request_sock *ireq = inet_rsk(req);
2875 struct tcp_sock *tp = tcp_sk(sk);
2877 struct sk_buff *skb;
2878 struct tcp_md5sig_key *md5;
2879 int tcp_header_size;
2882 skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
2883 if (unlikely(!skb)) {
2887 /* Reserve space for headers. */
2888 skb_reserve(skb, MAX_TCP_HEADER);
2890 skb_dst_set(skb, dst);
2891 security_skb_owned_by(skb, sk);
2893 mss = dst_metric_advmss(dst);
2894 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
2895 mss = tp->rx_opt.user_mss;
2897 memset(&opts, 0, sizeof(opts));
2898 #ifdef CONFIG_SYN_COOKIES
2899 if (unlikely(req->cookie_ts))
2900 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
2903 skb_mstamp_get(&skb->skb_mstamp);
2904 tcp_header_size = tcp_synack_options(sk, req, mss, skb, &opts, &md5,
2907 skb_push(skb, tcp_header_size);
2908 skb_reset_transport_header(skb);
2911 memset(th, 0, sizeof(struct tcphdr));
2914 tcp_ecn_make_synack(req, th, sk);
2915 th->source = htons(ireq->ir_num);
2916 th->dest = ireq->ir_rmt_port;
2917 /* Setting of flags are superfluous here for callers (and ECE is
2918 * not even correctly set)
2920 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn,
2921 TCPHDR_SYN | TCPHDR_ACK);
2923 th->seq = htonl(TCP_SKB_CB(skb)->seq);
2924 /* XXX data is queued and acked as is. No buffer/window check */
2925 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
2927 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
2928 th->window = htons(min(req->rcv_wnd, 65535U));
2929 tcp_options_write((__be32 *)(th + 1), tp, &opts);
2930 th->doff = (tcp_header_size >> 2);
2931 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
2933 #ifdef CONFIG_TCP_MD5SIG
2934 /* Okay, we have all we need - do the md5 hash if needed */
2936 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
2937 md5, NULL, req, skb);
2943 EXPORT_SYMBOL(tcp_make_synack);
2945 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
2947 struct inet_connection_sock *icsk = inet_csk(sk);
2948 const struct tcp_congestion_ops *ca;
2949 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
2951 if (ca_key == TCP_CA_UNSPEC)
2955 ca = tcp_ca_find_key(ca_key);
2956 if (likely(ca && try_module_get(ca->owner))) {
2957 module_put(icsk->icsk_ca_ops->owner);
2958 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
2959 icsk->icsk_ca_ops = ca;
2964 /* Do all connect socket setups that can be done AF independent. */
2965 static void tcp_connect_init(struct sock *sk)
2967 const struct dst_entry *dst = __sk_dst_get(sk);
2968 struct tcp_sock *tp = tcp_sk(sk);
2971 /* We'll fix this up when we get a response from the other end.
2972 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
2974 tp->tcp_header_len = sizeof(struct tcphdr) +
2975 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
2977 #ifdef CONFIG_TCP_MD5SIG
2978 if (tp->af_specific->md5_lookup(sk, sk) != NULL)
2979 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
2982 /* If user gave his TCP_MAXSEG, record it to clamp */
2983 if (tp->rx_opt.user_mss)
2984 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
2987 tcp_sync_mss(sk, dst_mtu(dst));
2989 tcp_ca_dst_init(sk, dst);
2991 if (!tp->window_clamp)
2992 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
2993 tp->advmss = dst_metric_advmss(dst);
2994 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
2995 tp->advmss = tp->rx_opt.user_mss;
2997 tcp_initialize_rcv_mss(sk);
2999 /* limit the window selection if the user enforce a smaller rx buffer */
3000 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3001 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3002 tp->window_clamp = tcp_full_space(sk);
3004 tcp_select_initial_window(tcp_full_space(sk),
3005 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3008 sysctl_tcp_window_scaling,
3010 dst_metric(dst, RTAX_INITRWND));
3012 tp->rx_opt.rcv_wscale = rcv_wscale;
3013 tp->rcv_ssthresh = tp->rcv_wnd;
3016 sock_reset_flag(sk, SOCK_DONE);
3019 tp->snd_una = tp->write_seq;
3020 tp->snd_sml = tp->write_seq;
3021 tp->snd_up = tp->write_seq;
3022 tp->snd_nxt = tp->write_seq;
3024 if (likely(!tp->repair))
3027 tp->rcv_tstamp = tcp_time_stamp;
3028 tp->rcv_wup = tp->rcv_nxt;
3029 tp->copied_seq = tp->rcv_nxt;
3031 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3032 inet_csk(sk)->icsk_retransmits = 0;
3033 tcp_clear_retrans(tp);
3036 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3038 struct tcp_sock *tp = tcp_sk(sk);
3039 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3041 tcb->end_seq += skb->len;
3042 __skb_header_release(skb);
3043 __tcp_add_write_queue_tail(sk, skb);
3044 sk->sk_wmem_queued += skb->truesize;
3045 sk_mem_charge(sk, skb->truesize);
3046 tp->write_seq = tcb->end_seq;
3047 tp->packets_out += tcp_skb_pcount(skb);
3050 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3051 * queue a data-only packet after the regular SYN, such that regular SYNs
3052 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3053 * only the SYN sequence, the data are retransmitted in the first ACK.
3054 * If cookie is not cached or other error occurs, falls back to send a
3055 * regular SYN with Fast Open cookie request option.
3057 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3059 struct tcp_sock *tp = tcp_sk(sk);
3060 struct tcp_fastopen_request *fo = tp->fastopen_req;
3061 int syn_loss = 0, space, err = 0, copied;
3062 unsigned long last_syn_loss = 0;
3063 struct sk_buff *syn_data;
3065 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3066 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3067 &syn_loss, &last_syn_loss);
3068 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3070 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3071 fo->cookie.len = -1;
3075 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3076 fo->cookie.len = -1;
3077 else if (fo->cookie.len <= 0)
3080 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3081 * user-MSS. Reserve maximum option space for middleboxes that add
3082 * private TCP options. The cost is reduced data space in SYN :(
3084 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3085 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3086 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3087 MAX_TCP_OPTION_SPACE;
3089 space = min_t(size_t, space, fo->size);
3091 /* limit to order-0 allocations */
3092 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3094 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation);
3097 syn_data->ip_summed = CHECKSUM_PARTIAL;
3098 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3099 copied = copy_from_iter(skb_put(syn_data, space), space,
3100 &fo->data->msg_iter);
3101 if (unlikely(!copied)) {
3102 kfree_skb(syn_data);
3105 if (copied != space) {
3106 skb_trim(syn_data, copied);
3110 /* No more data pending in inet_wait_for_connect() */
3111 if (space == fo->size)
3115 tcp_connect_queue_skb(sk, syn_data);
3117 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3119 syn->skb_mstamp = syn_data->skb_mstamp;
3121 /* Now full SYN+DATA was cloned and sent (or not),
3122 * remove the SYN from the original skb (syn_data)
3123 * we keep in write queue in case of a retransmit, as we
3124 * also have the SYN packet (with no data) in the same queue.
3126 TCP_SKB_CB(syn_data)->seq++;
3127 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3129 tp->syn_data = (fo->copied > 0);
3130 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3135 /* Send a regular SYN with Fast Open cookie request option */
3136 if (fo->cookie.len > 0)
3138 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3140 tp->syn_fastopen = 0;
3142 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3146 /* Build a SYN and send it off. */
3147 int tcp_connect(struct sock *sk)
3149 struct tcp_sock *tp = tcp_sk(sk);
3150 struct sk_buff *buff;
3153 tcp_connect_init(sk);
3155 if (unlikely(tp->repair)) {
3156 tcp_finish_connect(sk, NULL);
3160 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
3161 if (unlikely(!buff))
3164 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3165 tp->retrans_stamp = tcp_time_stamp;
3166 tcp_connect_queue_skb(sk, buff);
3167 tcp_ecn_send_syn(sk, buff);
3169 /* Send off SYN; include data in Fast Open. */
3170 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3171 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3172 if (err == -ECONNREFUSED)
3175 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3176 * in order to make this packet get counted in tcpOutSegs.
3178 tp->snd_nxt = tp->write_seq;
3179 tp->pushed_seq = tp->write_seq;
3180 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3182 /* Timer for repeating the SYN until an answer. */
3183 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3184 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3187 EXPORT_SYMBOL(tcp_connect);
3189 /* Send out a delayed ack, the caller does the policy checking
3190 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3193 void tcp_send_delayed_ack(struct sock *sk)
3195 struct inet_connection_sock *icsk = inet_csk(sk);
3196 int ato = icsk->icsk_ack.ato;
3197 unsigned long timeout;
3199 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
3201 if (ato > TCP_DELACK_MIN) {
3202 const struct tcp_sock *tp = tcp_sk(sk);
3203 int max_ato = HZ / 2;
3205 if (icsk->icsk_ack.pingpong ||
3206 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3207 max_ato = TCP_DELACK_MAX;
3209 /* Slow path, intersegment interval is "high". */
3211 /* If some rtt estimate is known, use it to bound delayed ack.
3212 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3216 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3223 ato = min(ato, max_ato);
3226 /* Stay within the limit we were given */
3227 timeout = jiffies + ato;
3229 /* Use new timeout only if there wasn't a older one earlier. */
3230 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3231 /* If delack timer was blocked or is about to expire,
3234 if (icsk->icsk_ack.blocked ||
3235 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3240 if (!time_before(timeout, icsk->icsk_ack.timeout))
3241 timeout = icsk->icsk_ack.timeout;
3243 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3244 icsk->icsk_ack.timeout = timeout;
3245 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3248 /* This routine sends an ack and also updates the window. */
3249 void tcp_send_ack(struct sock *sk)
3251 struct sk_buff *buff;
3253 /* If we have been reset, we may not send again. */
3254 if (sk->sk_state == TCP_CLOSE)
3257 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
3259 /* We are not putting this on the write queue, so
3260 * tcp_transmit_skb() will set the ownership to this
3263 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3265 inet_csk_schedule_ack(sk);
3266 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3267 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3268 TCP_DELACK_MAX, TCP_RTO_MAX);
3272 /* Reserve space for headers and prepare control bits. */
3273 skb_reserve(buff, MAX_TCP_HEADER);
3274 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3276 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3278 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3279 * We also avoid tcp_wfree() overhead (cache line miss accessing
3280 * tp->tsq_flags) by using regular sock_wfree()
3282 skb_set_tcp_pure_ack(buff);
3284 /* Send it off, this clears delayed acks for us. */
3285 skb_mstamp_get(&buff->skb_mstamp);
3286 tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC));
3288 EXPORT_SYMBOL_GPL(tcp_send_ack);
3290 /* This routine sends a packet with an out of date sequence
3291 * number. It assumes the other end will try to ack it.
3293 * Question: what should we make while urgent mode?
3294 * 4.4BSD forces sending single byte of data. We cannot send
3295 * out of window data, because we have SND.NXT==SND.MAX...
3297 * Current solution: to send TWO zero-length segments in urgent mode:
3298 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3299 * out-of-date with SND.UNA-1 to probe window.
3301 static int tcp_xmit_probe_skb(struct sock *sk, int urgent)
3303 struct tcp_sock *tp = tcp_sk(sk);
3304 struct sk_buff *skb;
3306 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3307 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3311 /* Reserve space for headers and set control bits. */
3312 skb_reserve(skb, MAX_TCP_HEADER);
3313 /* Use a previous sequence. This should cause the other
3314 * end to send an ack. Don't queue or clone SKB, just
3317 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3318 skb_mstamp_get(&skb->skb_mstamp);
3319 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3322 void tcp_send_window_probe(struct sock *sk)
3324 if (sk->sk_state == TCP_ESTABLISHED) {
3325 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3326 tcp_xmit_probe_skb(sk, 0);
3330 /* Initiate keepalive or window probe from timer. */
3331 int tcp_write_wakeup(struct sock *sk)
3333 struct tcp_sock *tp = tcp_sk(sk);
3334 struct sk_buff *skb;
3336 if (sk->sk_state == TCP_CLOSE)
3339 if ((skb = tcp_send_head(sk)) != NULL &&
3340 before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3342 unsigned int mss = tcp_current_mss(sk);
3343 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3345 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3346 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3348 /* We are probing the opening of a window
3349 * but the window size is != 0
3350 * must have been a result SWS avoidance ( sender )
3352 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3354 seg_size = min(seg_size, mss);
3355 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3356 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3358 } else if (!tcp_skb_pcount(skb))
3359 tcp_set_skb_tso_segs(sk, skb, mss);
3361 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3362 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3364 tcp_event_new_data_sent(sk, skb);
3367 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3368 tcp_xmit_probe_skb(sk, 1);
3369 return tcp_xmit_probe_skb(sk, 0);
3373 /* A window probe timeout has occurred. If window is not closed send
3374 * a partial packet else a zero probe.
3376 void tcp_send_probe0(struct sock *sk)
3378 struct inet_connection_sock *icsk = inet_csk(sk);
3379 struct tcp_sock *tp = tcp_sk(sk);
3380 unsigned long probe_max;
3383 err = tcp_write_wakeup(sk);
3385 if (tp->packets_out || !tcp_send_head(sk)) {
3386 /* Cancel probe timer, if it is not required. */
3387 icsk->icsk_probes_out = 0;
3388 icsk->icsk_backoff = 0;
3393 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3394 icsk->icsk_backoff++;
3395 icsk->icsk_probes_out++;
3396 probe_max = TCP_RTO_MAX;
3398 /* If packet was not sent due to local congestion,
3399 * do not backoff and do not remember icsk_probes_out.
3400 * Let local senders to fight for local resources.
3402 * Use accumulated backoff yet.
3404 if (!icsk->icsk_probes_out)
3405 icsk->icsk_probes_out = 1;
3406 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3408 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3409 inet_csk_rto_backoff(icsk, probe_max),
3413 int tcp_rtx_synack(struct sock *sk, struct request_sock *req)
3415 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3419 res = af_ops->send_synack(sk, NULL, &fl, req, 0, NULL);
3421 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3422 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3426 EXPORT_SYMBOL(tcp_rtx_synack);