1 /*
2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
5 *
6 * Implementation of the Transmission Control Protocol(TCP).
7 *
8 * Authors: Ross Biro
9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
10 * Mark Evans, <evansmp@uhura.aston.ac.uk>
11 * Corey Minyard <wf-rch!minyard@relay.EU.net>
12 * Florian La Roche, <flla@stud.uni-sb.de>
13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
14 * Linus Torvalds, <torvalds@cs.helsinki.fi>
15 * Alan Cox, <gw4pts@gw4pts.ampr.org>
16 * Matthew Dillon, <dillon@apollo.west.oic.com>
17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
18 * Jorge Cwik, <jorge@laser.satlink.net>
19 */
20
21 /*
22 * Changes: Pedro Roque : Retransmit queue handled by TCP.
23 * : Fragmentation on mtu decrease
24 * : Segment collapse on retransmit
25 * : AF independence
26 *
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
34 *
35 */
36
37 #define pr_fmt(fmt) "TCP: " fmt
38
39 #include <net/tcp.h>
40
41 #include <linux/compiler.h>
42 #include <linux/gfp.h>
43 #include <linux/module.h>
44
45 /* People can turn this off for buggy TCP's found in printers etc. */
46 int sysctl_tcp_retrans_collapse __read_mostly = 1;
47
48 /* People can turn this on to work with those rare, broken TCPs that
49 * interpret the window field as a signed quantity.
50 */
51 int sysctl_tcp_workaround_signed_windows __read_mostly = 0;
52
53 /* Default TSQ limit of four TSO segments */
54 int sysctl_tcp_limit_output_bytes __read_mostly = 262144;
55
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.
59 */
60 int sysctl_tcp_tso_win_divisor __read_mostly = 3;
61
62 /* By default, RFC2861 behavior. */
63 int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
64
65 unsigned int sysctl_tcp_notsent_lowat __read_mostly = UINT_MAX;
66 EXPORT_SYMBOL(sysctl_tcp_notsent_lowat);
67
68 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
69 int push_one, gfp_t gfp);
70
71 /* Account for new data that has been sent to the network. */
tcp_event_new_data_sent(struct sock * sk,const struct sk_buff * skb)72 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
73 {
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;
77
78 tcp_advance_send_head(sk, skb);
79 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
80
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) {
84 tcp_rearm_rto(sk);
85 }
86
87 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
88 tcp_skb_pcount(skb));
89 }
90
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:
96 */
tcp_acceptable_seq(const struct sock * sk)97 static inline __u32 tcp_acceptable_seq(const struct sock *sk)
98 {
99 const struct tcp_sock *tp = tcp_sk(sk);
100
101 if (!before(tcp_wnd_end(tp), tp->snd_nxt))
102 return tp->snd_nxt;
103 else
104 return tcp_wnd_end(tp);
105 }
106
107 /* Calculate mss to advertise in SYN segment.
108 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that:
109 *
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
114 * large MSS.
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".
120 */
tcp_advertise_mss(struct sock * sk)121 static __u16 tcp_advertise_mss(struct sock *sk)
122 {
123 struct tcp_sock *tp = tcp_sk(sk);
124 const struct dst_entry *dst = __sk_dst_get(sk);
125 int mss = tp->advmss;
126
127 if (dst) {
128 unsigned int metric = dst_metric_advmss(dst);
129
130 if (metric < mss) {
131 mss = metric;
132 tp->advmss = mss;
133 }
134 }
135
136 return (__u16)mss;
137 }
138
139 /* RFC2861. Reset CWND after idle period longer RTO to "restart window".
140 * This is the first part of cwnd validation mechanism.
141 */
tcp_cwnd_restart(struct sock * sk,s32 delta)142 void tcp_cwnd_restart(struct sock *sk, s32 delta)
143 {
144 struct tcp_sock *tp = tcp_sk(sk);
145 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
146 u32 cwnd = tp->snd_cwnd;
147
148 tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
149
150 tp->snd_ssthresh = tcp_current_ssthresh(sk);
151 restart_cwnd = min(restart_cwnd, cwnd);
152
153 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
154 cwnd >>= 1;
155 tp->snd_cwnd = max(cwnd, restart_cwnd);
156 tp->snd_cwnd_stamp = tcp_time_stamp;
157 tp->snd_cwnd_used = 0;
158 }
159
160 /* Congestion state accounting after a packet has been sent. */
tcp_event_data_sent(struct tcp_sock * tp,struct sock * sk)161 static void tcp_event_data_sent(struct tcp_sock *tp,
162 struct sock *sk)
163 {
164 struct inet_connection_sock *icsk = inet_csk(sk);
165 const u32 now = tcp_time_stamp;
166
167 if (tcp_packets_in_flight(tp) == 0)
168 tcp_ca_event(sk, CA_EVENT_TX_START);
169
170 tp->lsndtime = now;
171
172 /* If it is a reply for ato after last received
173 * packet, enter pingpong mode.
174 */
175 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
176 icsk->icsk_ack.pingpong = 1;
177 }
178
179 /* Account for an ACK we sent. */
tcp_event_ack_sent(struct sock * sk,unsigned int pkts,u32 rcv_nxt)180 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts,
181 u32 rcv_nxt)
182 {
183 struct tcp_sock *tp = tcp_sk(sk);
184
185 if (unlikely(rcv_nxt != tp->rcv_nxt))
186 return; /* Special ACK sent by DCTCP to reflect ECN */
187 tcp_dec_quickack_mode(sk, pkts);
188 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
189 }
190
191
tcp_default_init_rwnd(u32 mss)192 u32 tcp_default_init_rwnd(u32 mss)
193 {
194 /* Initial receive window should be twice of TCP_INIT_CWND to
195 * enable proper sending of new unsent data during fast recovery
196 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a
197 * limit when mss is larger than 1460.
198 */
199 u32 init_rwnd = sysctl_tcp_default_init_rwnd;
200
201 if (mss > 1460)
202 init_rwnd = max((1460 * init_rwnd) / mss, 2U);
203 return init_rwnd;
204 }
205
206 /* Determine a window scaling and initial window to offer.
207 * Based on the assumption that the given amount of space
208 * will be offered. Store the results in the tp structure.
209 * NOTE: for smooth operation initial space offering should
210 * be a multiple of mss if possible. We assume here that mss >= 1.
211 * This MUST be enforced by all callers.
212 */
tcp_select_initial_window(int __space,__u32 mss,__u32 * rcv_wnd,__u32 * window_clamp,int wscale_ok,__u8 * rcv_wscale,__u32 init_rcv_wnd)213 void tcp_select_initial_window(int __space, __u32 mss,
214 __u32 *rcv_wnd, __u32 *window_clamp,
215 int wscale_ok, __u8 *rcv_wscale,
216 __u32 init_rcv_wnd)
217 {
218 unsigned int space = (__space < 0 ? 0 : __space);
219
220 /* If no clamp set the clamp to the max possible scaled window */
221 if (*window_clamp == 0)
222 (*window_clamp) = (65535 << 14);
223 space = min(*window_clamp, space);
224
225 /* Quantize space offering to a multiple of mss if possible. */
226 if (space > mss)
227 space = (space / mss) * mss;
228
229 /* NOTE: offering an initial window larger than 32767
230 * will break some buggy TCP stacks. If the admin tells us
231 * it is likely we could be speaking with such a buggy stack
232 * we will truncate our initial window offering to 32K-1
233 * unless the remote has sent us a window scaling option,
234 * which we interpret as a sign the remote TCP is not
235 * misinterpreting the window field as a signed quantity.
236 */
237 if (sysctl_tcp_workaround_signed_windows)
238 (*rcv_wnd) = min(space, MAX_TCP_WINDOW);
239 else
240 (*rcv_wnd) = space;
241
242 (*rcv_wscale) = 0;
243 if (wscale_ok) {
244 /* Set window scaling on max possible window
245 * See RFC1323 for an explanation of the limit to 14
246 */
247 space = max_t(u32, space, sysctl_tcp_rmem[2]);
248 space = max_t(u32, space, sysctl_rmem_max);
249 space = min_t(u32, space, *window_clamp);
250 while (space > 65535 && (*rcv_wscale) < 14) {
251 space >>= 1;
252 (*rcv_wscale)++;
253 }
254 }
255
256 if (mss > (1 << *rcv_wscale)) {
257 if (!init_rcv_wnd) /* Use default unless specified otherwise */
258 init_rcv_wnd = tcp_default_init_rwnd(mss);
259 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
260 }
261
262 /* Set the clamp no higher than max representable value */
263 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp);
264 }
265 EXPORT_SYMBOL(tcp_select_initial_window);
266
267 /* Chose a new window to advertise, update state in tcp_sock for the
268 * socket, and return result with RFC1323 scaling applied. The return
269 * value can be stuffed directly into th->window for an outgoing
270 * frame.
271 */
tcp_select_window(struct sock * sk)272 static u16 tcp_select_window(struct sock *sk)
273 {
274 struct tcp_sock *tp = tcp_sk(sk);
275 u32 old_win = tp->rcv_wnd;
276 u32 cur_win = tcp_receive_window(tp);
277 u32 new_win = __tcp_select_window(sk);
278
279 /* Never shrink the offered window */
280 if (new_win < cur_win) {
281 /* Danger Will Robinson!
282 * Don't update rcv_wup/rcv_wnd here or else
283 * we will not be able to advertise a zero
284 * window in time. --DaveM
285 *
286 * Relax Will Robinson.
287 */
288 if (new_win == 0)
289 NET_INC_STATS(sock_net(sk),
290 LINUX_MIB_TCPWANTZEROWINDOWADV);
291 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale);
292 }
293 tp->rcv_wnd = new_win;
294 tp->rcv_wup = tp->rcv_nxt;
295
296 /* Make sure we do not exceed the maximum possible
297 * scaled window.
298 */
299 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows)
300 new_win = min(new_win, MAX_TCP_WINDOW);
301 else
302 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
303
304 /* RFC1323 scaling applied */
305 new_win >>= tp->rx_opt.rcv_wscale;
306
307 /* If we advertise zero window, disable fast path. */
308 if (new_win == 0) {
309 tp->pred_flags = 0;
310 if (old_win)
311 NET_INC_STATS(sock_net(sk),
312 LINUX_MIB_TCPTOZEROWINDOWADV);
313 } else if (old_win == 0) {
314 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV);
315 }
316
317 return new_win;
318 }
319
320 /* Packet ECN state for a SYN-ACK */
tcp_ecn_send_synack(struct sock * sk,struct sk_buff * skb)321 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb)
322 {
323 const struct tcp_sock *tp = tcp_sk(sk);
324
325 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR;
326 if (!(tp->ecn_flags & TCP_ECN_OK))
327 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE;
328 else if (tcp_ca_needs_ecn(sk))
329 INET_ECN_xmit(sk);
330 }
331
332 /* Packet ECN state for a SYN. */
tcp_ecn_send_syn(struct sock * sk,struct sk_buff * skb)333 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
334 {
335 struct tcp_sock *tp = tcp_sk(sk);
336 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 ||
337 tcp_ca_needs_ecn(sk);
338
339 if (!use_ecn) {
340 const struct dst_entry *dst = __sk_dst_get(sk);
341
342 if (dst && dst_feature(dst, RTAX_FEATURE_ECN))
343 use_ecn = true;
344 }
345
346 tp->ecn_flags = 0;
347
348 if (use_ecn) {
349 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR;
350 tp->ecn_flags = TCP_ECN_OK;
351 if (tcp_ca_needs_ecn(sk))
352 INET_ECN_xmit(sk);
353 }
354 }
355
tcp_ecn_clear_syn(struct sock * sk,struct sk_buff * skb)356 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
357 {
358 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
359 /* tp->ecn_flags are cleared at a later point in time when
360 * SYN ACK is ultimatively being received.
361 */
362 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR);
363 }
364
365 static void
tcp_ecn_make_synack(const struct request_sock * req,struct tcphdr * th)366 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
367 {
368 if (inet_rsk(req)->ecn_ok)
369 th->ece = 1;
370 }
371
372 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to
373 * be sent.
374 */
tcp_ecn_send(struct sock * sk,struct sk_buff * skb,int tcp_header_len)375 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
376 int tcp_header_len)
377 {
378 struct tcp_sock *tp = tcp_sk(sk);
379
380 if (tp->ecn_flags & TCP_ECN_OK) {
381 /* Not-retransmitted data segment: set ECT and inject CWR. */
382 if (skb->len != tcp_header_len &&
383 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
384 INET_ECN_xmit(sk);
385 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) {
386 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
387 tcp_hdr(skb)->cwr = 1;
388 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN;
389 }
390 } else if (!tcp_ca_needs_ecn(sk)) {
391 /* ACK or retransmitted segment: clear ECT|CE */
392 INET_ECN_dontxmit(sk);
393 }
394 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR)
395 tcp_hdr(skb)->ece = 1;
396 }
397 }
398
399 /* Constructs common control bits of non-data skb. If SYN/FIN is present,
400 * auto increment end seqno.
401 */
tcp_init_nondata_skb(struct sk_buff * skb,u32 seq,u8 flags)402 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags)
403 {
404 skb->ip_summed = CHECKSUM_PARTIAL;
405 skb->csum = 0;
406
407 TCP_SKB_CB(skb)->tcp_flags = flags;
408 TCP_SKB_CB(skb)->sacked = 0;
409
410 tcp_skb_pcount_set(skb, 1);
411
412 TCP_SKB_CB(skb)->seq = seq;
413 if (flags & (TCPHDR_SYN | TCPHDR_FIN))
414 seq++;
415 TCP_SKB_CB(skb)->end_seq = seq;
416 }
417
tcp_urg_mode(const struct tcp_sock * tp)418 static inline bool tcp_urg_mode(const struct tcp_sock *tp)
419 {
420 return tp->snd_una != tp->snd_up;
421 }
422
423 #define OPTION_SACK_ADVERTISE (1 << 0)
424 #define OPTION_TS (1 << 1)
425 #define OPTION_MD5 (1 << 2)
426 #define OPTION_WSCALE (1 << 3)
427 #define OPTION_FAST_OPEN_COOKIE (1 << 8)
428
429 struct tcp_out_options {
430 u16 options; /* bit field of OPTION_* */
431 u16 mss; /* 0 to disable */
432 u8 ws; /* window scale, 0 to disable */
433 u8 num_sack_blocks; /* number of SACK blocks to include */
434 u8 hash_size; /* bytes in hash_location */
435 __u8 *hash_location; /* temporary pointer, overloaded */
436 __u32 tsval, tsecr; /* need to include OPTION_TS */
437 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */
438 };
439
440 /* Write previously computed TCP options to the packet.
441 *
442 * Beware: Something in the Internet is very sensitive to the ordering of
443 * TCP options, we learned this through the hard way, so be careful here.
444 * Luckily we can at least blame others for their non-compliance but from
445 * inter-operability perspective it seems that we're somewhat stuck with
446 * the ordering which we have been using if we want to keep working with
447 * those broken things (not that it currently hurts anybody as there isn't
448 * particular reason why the ordering would need to be changed).
449 *
450 * At least SACK_PERM as the first option is known to lead to a disaster
451 * (but it may well be that other scenarios fail similarly).
452 */
tcp_options_write(__be32 * ptr,struct tcp_sock * tp,struct tcp_out_options * opts)453 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp,
454 struct tcp_out_options *opts)
455 {
456 u16 options = opts->options; /* mungable copy */
457
458 if (unlikely(OPTION_MD5 & options)) {
459 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
460 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG);
461 /* overload cookie hash location */
462 opts->hash_location = (__u8 *)ptr;
463 ptr += 4;
464 }
465
466 if (unlikely(opts->mss)) {
467 *ptr++ = htonl((TCPOPT_MSS << 24) |
468 (TCPOLEN_MSS << 16) |
469 opts->mss);
470 }
471
472 if (likely(OPTION_TS & options)) {
473 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
474 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) |
475 (TCPOLEN_SACK_PERM << 16) |
476 (TCPOPT_TIMESTAMP << 8) |
477 TCPOLEN_TIMESTAMP);
478 options &= ~OPTION_SACK_ADVERTISE;
479 } else {
480 *ptr++ = htonl((TCPOPT_NOP << 24) |
481 (TCPOPT_NOP << 16) |
482 (TCPOPT_TIMESTAMP << 8) |
483 TCPOLEN_TIMESTAMP);
484 }
485 *ptr++ = htonl(opts->tsval);
486 *ptr++ = htonl(opts->tsecr);
487 }
488
489 if (unlikely(OPTION_SACK_ADVERTISE & options)) {
490 *ptr++ = htonl((TCPOPT_NOP << 24) |
491 (TCPOPT_NOP << 16) |
492 (TCPOPT_SACK_PERM << 8) |
493 TCPOLEN_SACK_PERM);
494 }
495
496 if (unlikely(OPTION_WSCALE & options)) {
497 *ptr++ = htonl((TCPOPT_NOP << 24) |
498 (TCPOPT_WINDOW << 16) |
499 (TCPOLEN_WINDOW << 8) |
500 opts->ws);
501 }
502
503 if (unlikely(opts->num_sack_blocks)) {
504 struct tcp_sack_block *sp = tp->rx_opt.dsack ?
505 tp->duplicate_sack : tp->selective_acks;
506 int this_sack;
507
508 *ptr++ = htonl((TCPOPT_NOP << 24) |
509 (TCPOPT_NOP << 16) |
510 (TCPOPT_SACK << 8) |
511 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks *
512 TCPOLEN_SACK_PERBLOCK)));
513
514 for (this_sack = 0; this_sack < opts->num_sack_blocks;
515 ++this_sack) {
516 *ptr++ = htonl(sp[this_sack].start_seq);
517 *ptr++ = htonl(sp[this_sack].end_seq);
518 }
519
520 tp->rx_opt.dsack = 0;
521 }
522
523 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) {
524 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie;
525 u8 *p = (u8 *)ptr;
526 u32 len; /* Fast Open option length */
527
528 if (foc->exp) {
529 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len;
530 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) |
531 TCPOPT_FASTOPEN_MAGIC);
532 p += TCPOLEN_EXP_FASTOPEN_BASE;
533 } else {
534 len = TCPOLEN_FASTOPEN_BASE + foc->len;
535 *p++ = TCPOPT_FASTOPEN;
536 *p++ = len;
537 }
538
539 memcpy(p, foc->val, foc->len);
540 if ((len & 3) == 2) {
541 p[foc->len] = TCPOPT_NOP;
542 p[foc->len + 1] = TCPOPT_NOP;
543 }
544 ptr += (len + 3) >> 2;
545 }
546 }
547
548 /* Compute TCP options for SYN packets. This is not the final
549 * network wire format yet.
550 */
tcp_syn_options(struct sock * sk,struct sk_buff * skb,struct tcp_out_options * opts,struct tcp_md5sig_key ** md5)551 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
552 struct tcp_out_options *opts,
553 struct tcp_md5sig_key **md5)
554 {
555 struct tcp_sock *tp = tcp_sk(sk);
556 unsigned int remaining = MAX_TCP_OPTION_SPACE;
557 struct tcp_fastopen_request *fastopen = tp->fastopen_req;
558
559 #ifdef CONFIG_TCP_MD5SIG
560 *md5 = tp->af_specific->md5_lookup(sk, sk);
561 if (*md5) {
562 opts->options |= OPTION_MD5;
563 remaining -= TCPOLEN_MD5SIG_ALIGNED;
564 }
565 #else
566 *md5 = NULL;
567 #endif
568
569 /* We always get an MSS option. The option bytes which will be seen in
570 * normal data packets should timestamps be used, must be in the MSS
571 * advertised. But we subtract them from tp->mss_cache so that
572 * calculations in tcp_sendmsg are simpler etc. So account for this
573 * fact here if necessary. If we don't do this correctly, as a
574 * receiver we won't recognize data packets as being full sized when we
575 * should, and thus we won't abide by the delayed ACK rules correctly.
576 * SACKs don't matter, we never delay an ACK when we have any of those
577 * going out. */
578 opts->mss = tcp_advertise_mss(sk);
579 remaining -= TCPOLEN_MSS_ALIGNED;
580
581 if (likely(sysctl_tcp_timestamps && !*md5)) {
582 opts->options |= OPTION_TS;
583 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset;
584 opts->tsecr = tp->rx_opt.ts_recent;
585 remaining -= TCPOLEN_TSTAMP_ALIGNED;
586 }
587 if (likely(sysctl_tcp_window_scaling)) {
588 opts->ws = tp->rx_opt.rcv_wscale;
589 opts->options |= OPTION_WSCALE;
590 remaining -= TCPOLEN_WSCALE_ALIGNED;
591 }
592 if (likely(sysctl_tcp_sack)) {
593 opts->options |= OPTION_SACK_ADVERTISE;
594 if (unlikely(!(OPTION_TS & opts->options)))
595 remaining -= TCPOLEN_SACKPERM_ALIGNED;
596 }
597
598 if (fastopen && fastopen->cookie.len >= 0) {
599 u32 need = fastopen->cookie.len;
600
601 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE :
602 TCPOLEN_FASTOPEN_BASE;
603 need = (need + 3) & ~3U; /* Align to 32 bits */
604 if (remaining >= need) {
605 opts->options |= OPTION_FAST_OPEN_COOKIE;
606 opts->fastopen_cookie = &fastopen->cookie;
607 remaining -= need;
608 tp->syn_fastopen = 1;
609 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
610 }
611 }
612
613 return MAX_TCP_OPTION_SPACE - remaining;
614 }
615
616 /* Set up TCP options for SYN-ACKs. */
tcp_synack_options(struct request_sock * req,unsigned int mss,struct sk_buff * skb,struct tcp_out_options * opts,const struct tcp_md5sig_key * md5,struct tcp_fastopen_cookie * foc)617 static unsigned int tcp_synack_options(struct request_sock *req,
618 unsigned int mss, struct sk_buff *skb,
619 struct tcp_out_options *opts,
620 const struct tcp_md5sig_key *md5,
621 struct tcp_fastopen_cookie *foc)
622 {
623 struct inet_request_sock *ireq = inet_rsk(req);
624 unsigned int remaining = MAX_TCP_OPTION_SPACE;
625
626 #ifdef CONFIG_TCP_MD5SIG
627 if (md5) {
628 opts->options |= OPTION_MD5;
629 remaining -= TCPOLEN_MD5SIG_ALIGNED;
630
631 /* We can't fit any SACK blocks in a packet with MD5 + TS
632 * options. There was discussion about disabling SACK
633 * rather than TS in order to fit in better with old,
634 * buggy kernels, but that was deemed to be unnecessary.
635 */
636 ireq->tstamp_ok &= !ireq->sack_ok;
637 }
638 #endif
639
640 /* We always send an MSS option. */
641 opts->mss = mss;
642 remaining -= TCPOLEN_MSS_ALIGNED;
643
644 if (likely(ireq->wscale_ok)) {
645 opts->ws = ireq->rcv_wscale;
646 opts->options |= OPTION_WSCALE;
647 remaining -= TCPOLEN_WSCALE_ALIGNED;
648 }
649 if (likely(ireq->tstamp_ok)) {
650 opts->options |= OPTION_TS;
651 opts->tsval = tcp_skb_timestamp(skb);
652 opts->tsecr = req->ts_recent;
653 remaining -= TCPOLEN_TSTAMP_ALIGNED;
654 }
655 if (likely(ireq->sack_ok)) {
656 opts->options |= OPTION_SACK_ADVERTISE;
657 if (unlikely(!ireq->tstamp_ok))
658 remaining -= TCPOLEN_SACKPERM_ALIGNED;
659 }
660 if (foc != NULL && foc->len >= 0) {
661 u32 need = foc->len;
662
663 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE :
664 TCPOLEN_FASTOPEN_BASE;
665 need = (need + 3) & ~3U; /* Align to 32 bits */
666 if (remaining >= need) {
667 opts->options |= OPTION_FAST_OPEN_COOKIE;
668 opts->fastopen_cookie = foc;
669 remaining -= need;
670 }
671 }
672
673 return MAX_TCP_OPTION_SPACE - remaining;
674 }
675
676 /* Compute TCP options for ESTABLISHED sockets. This is not the
677 * final wire format yet.
678 */
tcp_established_options(struct sock * sk,struct sk_buff * skb,struct tcp_out_options * opts,struct tcp_md5sig_key ** md5)679 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb,
680 struct tcp_out_options *opts,
681 struct tcp_md5sig_key **md5)
682 {
683 struct tcp_sock *tp = tcp_sk(sk);
684 unsigned int size = 0;
685 unsigned int eff_sacks;
686
687 opts->options = 0;
688
689 #ifdef CONFIG_TCP_MD5SIG
690 *md5 = tp->af_specific->md5_lookup(sk, sk);
691 if (unlikely(*md5)) {
692 opts->options |= OPTION_MD5;
693 size += TCPOLEN_MD5SIG_ALIGNED;
694 }
695 #else
696 *md5 = NULL;
697 #endif
698
699 if (likely(tp->rx_opt.tstamp_ok)) {
700 opts->options |= OPTION_TS;
701 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0;
702 opts->tsecr = tp->rx_opt.ts_recent;
703 size += TCPOLEN_TSTAMP_ALIGNED;
704 }
705
706 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack;
707 if (unlikely(eff_sacks)) {
708 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size;
709 opts->num_sack_blocks =
710 min_t(unsigned int, eff_sacks,
711 (remaining - TCPOLEN_SACK_BASE_ALIGNED) /
712 TCPOLEN_SACK_PERBLOCK);
713 if (likely(opts->num_sack_blocks))
714 size += TCPOLEN_SACK_BASE_ALIGNED +
715 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK;
716 }
717
718 return size;
719 }
720
721
722 /* TCP SMALL QUEUES (TSQ)
723 *
724 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev)
725 * to reduce RTT and bufferbloat.
726 * We do this using a special skb destructor (tcp_wfree).
727 *
728 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb
729 * needs to be reallocated in a driver.
730 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc
731 *
732 * Since transmit from skb destructor is forbidden, we use a tasklet
733 * to process all sockets that eventually need to send more skbs.
734 * We use one tasklet per cpu, with its own queue of sockets.
735 */
736 struct tsq_tasklet {
737 struct tasklet_struct tasklet;
738 struct list_head head; /* queue of tcp sockets */
739 };
740 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet);
741
tcp_tsq_handler(struct sock * sk)742 static void tcp_tsq_handler(struct sock *sk)
743 {
744 if ((1 << sk->sk_state) &
745 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING |
746 TCPF_CLOSE_WAIT | TCPF_LAST_ACK))
747 tcp_write_xmit(sk, tcp_current_mss(sk), tcp_sk(sk)->nonagle,
748 0, GFP_ATOMIC);
749 }
750 /*
751 * One tasklet per cpu tries to send more skbs.
752 * We run in tasklet context but need to disable irqs when
753 * transferring tsq->head because tcp_wfree() might
754 * interrupt us (non NAPI drivers)
755 */
tcp_tasklet_func(unsigned long data)756 static void tcp_tasklet_func(unsigned long data)
757 {
758 struct tsq_tasklet *tsq = (struct tsq_tasklet *)data;
759 LIST_HEAD(list);
760 unsigned long flags;
761 struct list_head *q, *n;
762 struct tcp_sock *tp;
763 struct sock *sk;
764
765 local_irq_save(flags);
766 list_splice_init(&tsq->head, &list);
767 local_irq_restore(flags);
768
769 list_for_each_safe(q, n, &list) {
770 tp = list_entry(q, struct tcp_sock, tsq_node);
771 list_del(&tp->tsq_node);
772
773 sk = (struct sock *)tp;
774 bh_lock_sock(sk);
775
776 if (!sock_owned_by_user(sk)) {
777 tcp_tsq_handler(sk);
778 } else {
779 /* defer the work to tcp_release_cb() */
780 set_bit(TCP_TSQ_DEFERRED, &tp->tsq_flags);
781 }
782 bh_unlock_sock(sk);
783
784 clear_bit(TSQ_QUEUED, &tp->tsq_flags);
785 sk_free(sk);
786 }
787 }
788
789 #define TCP_DEFERRED_ALL ((1UL << TCP_TSQ_DEFERRED) | \
790 (1UL << TCP_WRITE_TIMER_DEFERRED) | \
791 (1UL << TCP_DELACK_TIMER_DEFERRED) | \
792 (1UL << TCP_MTU_REDUCED_DEFERRED))
793 /**
794 * tcp_release_cb - tcp release_sock() callback
795 * @sk: socket
796 *
797 * called from release_sock() to perform protocol dependent
798 * actions before socket release.
799 */
tcp_release_cb(struct sock * sk)800 void tcp_release_cb(struct sock *sk)
801 {
802 struct tcp_sock *tp = tcp_sk(sk);
803 unsigned long flags, nflags;
804
805 /* perform an atomic operation only if at least one flag is set */
806 do {
807 flags = tp->tsq_flags;
808 if (!(flags & TCP_DEFERRED_ALL))
809 return;
810 nflags = flags & ~TCP_DEFERRED_ALL;
811 } while (cmpxchg(&tp->tsq_flags, flags, nflags) != flags);
812
813 if (flags & (1UL << TCP_TSQ_DEFERRED))
814 tcp_tsq_handler(sk);
815
816 /* Here begins the tricky part :
817 * We are called from release_sock() with :
818 * 1) BH disabled
819 * 2) sk_lock.slock spinlock held
820 * 3) socket owned by us (sk->sk_lock.owned == 1)
821 *
822 * But following code is meant to be called from BH handlers,
823 * so we should keep BH disabled, but early release socket ownership
824 */
825 sock_release_ownership(sk);
826
827 if (flags & (1UL << TCP_WRITE_TIMER_DEFERRED)) {
828 tcp_write_timer_handler(sk);
829 __sock_put(sk);
830 }
831 if (flags & (1UL << TCP_DELACK_TIMER_DEFERRED)) {
832 tcp_delack_timer_handler(sk);
833 __sock_put(sk);
834 }
835 if (flags & (1UL << TCP_MTU_REDUCED_DEFERRED)) {
836 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk);
837 __sock_put(sk);
838 }
839 }
840 EXPORT_SYMBOL(tcp_release_cb);
841
tcp_tasklet_init(void)842 void __init tcp_tasklet_init(void)
843 {
844 int i;
845
846 for_each_possible_cpu(i) {
847 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i);
848
849 INIT_LIST_HEAD(&tsq->head);
850 tasklet_init(&tsq->tasklet,
851 tcp_tasklet_func,
852 (unsigned long)tsq);
853 }
854 }
855
856 /*
857 * Write buffer destructor automatically called from kfree_skb.
858 * We can't xmit new skbs from this context, as we might already
859 * hold qdisc lock.
860 */
tcp_wfree(struct sk_buff * skb)861 void tcp_wfree(struct sk_buff *skb)
862 {
863 struct sock *sk = skb->sk;
864 struct tcp_sock *tp = tcp_sk(sk);
865 int wmem;
866
867 /* Keep one reference on sk_wmem_alloc.
868 * Will be released by sk_free() from here or tcp_tasklet_func()
869 */
870 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc);
871
872 /* If this softirq is serviced by ksoftirqd, we are likely under stress.
873 * Wait until our queues (qdisc + devices) are drained.
874 * This gives :
875 * - less callbacks to tcp_write_xmit(), reducing stress (batches)
876 * - chance for incoming ACK (processed by another cpu maybe)
877 * to migrate this flow (skb->ooo_okay will be eventually set)
878 */
879 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
880 goto out;
881
882 if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
883 !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
884 unsigned long flags;
885 struct tsq_tasklet *tsq;
886
887 /* queue this socket to tasklet queue */
888 local_irq_save(flags);
889 tsq = this_cpu_ptr(&tsq_tasklet);
890 list_add(&tp->tsq_node, &tsq->head);
891 tasklet_schedule(&tsq->tasklet);
892 local_irq_restore(flags);
893 return;
894 }
895 out:
896 sk_free(sk);
897 }
898
899 /* This routine actually transmits TCP packets queued in by
900 * tcp_do_sendmsg(). This is used by both the initial
901 * transmission and possible later retransmissions.
902 * All SKB's seen here are completely headerless. It is our
903 * job to build the TCP header, and pass the packet down to
904 * IP so it can do the same plus pass the packet off to the
905 * device.
906 *
907 * We are working here with either a clone of the original
908 * SKB, or a fresh unique copy made by the retransmit engine.
909 */
__tcp_transmit_skb(struct sock * sk,struct sk_buff * skb,int clone_it,gfp_t gfp_mask,u32 rcv_nxt)910 static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
911 int clone_it, gfp_t gfp_mask, u32 rcv_nxt)
912 {
913 const struct inet_connection_sock *icsk = inet_csk(sk);
914 struct inet_sock *inet;
915 struct tcp_sock *tp;
916 struct tcp_skb_cb *tcb;
917 struct tcp_out_options opts;
918 unsigned int tcp_options_size, tcp_header_size;
919 struct tcp_md5sig_key *md5;
920 struct tcphdr *th;
921 int err;
922
923 BUG_ON(!skb || !tcp_skb_pcount(skb));
924
925 if (clone_it) {
926 skb_mstamp_get(&skb->skb_mstamp);
927
928 if (unlikely(skb_cloned(skb)))
929 skb = pskb_copy(skb, gfp_mask);
930 else
931 skb = skb_clone(skb, gfp_mask);
932 if (unlikely(!skb))
933 return -ENOBUFS;
934 }
935
936 inet = inet_sk(sk);
937 tp = tcp_sk(sk);
938 tcb = TCP_SKB_CB(skb);
939 memset(&opts, 0, sizeof(opts));
940
941 if (unlikely(tcb->tcp_flags & TCPHDR_SYN))
942 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5);
943 else
944 tcp_options_size = tcp_established_options(sk, skb, &opts,
945 &md5);
946 tcp_header_size = tcp_options_size + sizeof(struct tcphdr);
947
948 /* if no packet is in qdisc/device queue, then allow XPS to select
949 * another queue. We can be called from tcp_tsq_handler()
950 * which holds one reference to sk_wmem_alloc.
951 *
952 * TODO: Ideally, in-flight pure ACK packets should not matter here.
953 * One way to get this would be to set skb->truesize = 2 on them.
954 */
955 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1);
956
957 skb_push(skb, tcp_header_size);
958 skb_reset_transport_header(skb);
959
960 skb_orphan(skb);
961 skb->sk = sk;
962 skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree;
963 skb_set_hash_from_sk(skb, sk);
964 atomic_add(skb->truesize, &sk->sk_wmem_alloc);
965
966 /* Build TCP header and checksum it. */
967 th = tcp_hdr(skb);
968 th->source = inet->inet_sport;
969 th->dest = inet->inet_dport;
970 th->seq = htonl(tcb->seq);
971 th->ack_seq = htonl(rcv_nxt);
972 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) |
973 tcb->tcp_flags);
974
975 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) {
976 /* RFC1323: The window in SYN & SYN/ACK segments
977 * is never scaled.
978 */
979 th->window = htons(min(tp->rcv_wnd, 65535U));
980 } else {
981 th->window = htons(tcp_select_window(sk));
982 }
983 th->check = 0;
984 th->urg_ptr = 0;
985
986 /* The urg_mode check is necessary during a below snd_una win probe */
987 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) {
988 if (before(tp->snd_up, tcb->seq + 0x10000)) {
989 th->urg_ptr = htons(tp->snd_up - tcb->seq);
990 th->urg = 1;
991 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
992 th->urg_ptr = htons(0xFFFF);
993 th->urg = 1;
994 }
995 }
996
997 tcp_options_write((__be32 *)(th + 1), tp, &opts);
998 skb_shinfo(skb)->gso_type = sk->sk_gso_type;
999 if (likely((tcb->tcp_flags & TCPHDR_SYN) == 0))
1000 tcp_ecn_send(sk, skb, tcp_header_size);
1001
1002 #ifdef CONFIG_TCP_MD5SIG
1003 /* Calculate the MD5 hash, as we have all we need now */
1004 if (md5) {
1005 sk_nocaps_add(sk, NETIF_F_GSO_MASK);
1006 tp->af_specific->calc_md5_hash(opts.hash_location,
1007 md5, sk, skb);
1008 }
1009 #endif
1010
1011 icsk->icsk_af_ops->send_check(sk, skb);
1012
1013 if (likely(tcb->tcp_flags & TCPHDR_ACK))
1014 tcp_event_ack_sent(sk, tcp_skb_pcount(skb), rcv_nxt);
1015
1016 if (skb->len != tcp_header_size)
1017 tcp_event_data_sent(tp, sk);
1018
1019 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq)
1020 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS,
1021 tcp_skb_pcount(skb));
1022
1023 tp->segs_out += tcp_skb_pcount(skb);
1024 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */
1025 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb);
1026 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb);
1027
1028 /* Our usage of tstamp should remain private */
1029 skb->tstamp.tv64 = 0;
1030
1031 /* Cleanup our debris for IP stacks */
1032 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm),
1033 sizeof(struct inet6_skb_parm)));
1034
1035 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
1036
1037 if (likely(err <= 0))
1038 return err;
1039
1040 tcp_enter_cwr(sk);
1041
1042 return net_xmit_eval(err);
1043 }
1044
tcp_transmit_skb(struct sock * sk,struct sk_buff * skb,int clone_it,gfp_t gfp_mask)1045 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
1046 gfp_t gfp_mask)
1047 {
1048 return __tcp_transmit_skb(sk, skb, clone_it, gfp_mask,
1049 tcp_sk(sk)->rcv_nxt);
1050 }
1051
1052 /* This routine just queues the buffer for sending.
1053 *
1054 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames,
1055 * otherwise socket can stall.
1056 */
tcp_queue_skb(struct sock * sk,struct sk_buff * skb)1057 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
1058 {
1059 struct tcp_sock *tp = tcp_sk(sk);
1060
1061 /* Advance write_seq and place onto the write_queue. */
1062 tp->write_seq = TCP_SKB_CB(skb)->end_seq;
1063 __skb_header_release(skb);
1064 tcp_add_write_queue_tail(sk, skb);
1065 sk->sk_wmem_queued += skb->truesize;
1066 sk_mem_charge(sk, skb->truesize);
1067 }
1068
1069 /* Initialize TSO segments for a packet. */
tcp_set_skb_tso_segs(struct sk_buff * skb,unsigned int mss_now)1070 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1071 {
1072 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
1073 /* Avoid the costly divide in the normal
1074 * non-TSO case.
1075 */
1076 tcp_skb_pcount_set(skb, 1);
1077 TCP_SKB_CB(skb)->tcp_gso_size = 0;
1078 } else {
1079 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
1080 TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
1081 }
1082 }
1083
1084 /* When a modification to fackets out becomes necessary, we need to check
1085 * skb is counted to fackets_out or not.
1086 */
tcp_adjust_fackets_out(struct sock * sk,const struct sk_buff * skb,int decr)1087 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb,
1088 int decr)
1089 {
1090 struct tcp_sock *tp = tcp_sk(sk);
1091
1092 if (!tp->sacked_out || tcp_is_reno(tp))
1093 return;
1094
1095 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq))
1096 tp->fackets_out -= decr;
1097 }
1098
1099 /* Pcount in the middle of the write queue got changed, we need to do various
1100 * tweaks to fix counters
1101 */
tcp_adjust_pcount(struct sock * sk,const struct sk_buff * skb,int decr)1102 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr)
1103 {
1104 struct tcp_sock *tp = tcp_sk(sk);
1105
1106 tp->packets_out -= decr;
1107
1108 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
1109 tp->sacked_out -= decr;
1110 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1111 tp->retrans_out -= decr;
1112 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
1113 tp->lost_out -= decr;
1114
1115 /* Reno case is special. Sigh... */
1116 if (tcp_is_reno(tp) && decr > 0)
1117 tp->sacked_out -= min_t(u32, tp->sacked_out, decr);
1118
1119 tcp_adjust_fackets_out(sk, skb, decr);
1120
1121 if (tp->lost_skb_hint &&
1122 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) &&
1123 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)))
1124 tp->lost_cnt_hint -= decr;
1125
1126 tcp_verify_left_out(tp);
1127 }
1128
tcp_fragment_tstamp(struct sk_buff * skb,struct sk_buff * skb2)1129 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
1130 {
1131 struct skb_shared_info *shinfo = skb_shinfo(skb);
1132
1133 if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
1134 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
1135 struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
1136 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
1137
1138 shinfo->tx_flags &= ~tsflags;
1139 shinfo2->tx_flags |= tsflags;
1140 swap(shinfo->tskey, shinfo2->tskey);
1141 }
1142 }
1143
1144 /* Function to create two new TCP segments. Shrinks the given segment
1145 * to the specified size and appends a new segment with the rest of the
1146 * packet to the list. This won't be called frequently, I hope.
1147 * Remember, these are still headerless SKBs at this point.
1148 */
tcp_fragment(struct sock * sk,struct sk_buff * skb,u32 len,unsigned int mss_now,gfp_t gfp)1149 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
1150 unsigned int mss_now, gfp_t gfp)
1151 {
1152 struct tcp_sock *tp = tcp_sk(sk);
1153 struct sk_buff *buff;
1154 int nsize, old_factor;
1155 long limit;
1156 int nlen;
1157 u8 flags;
1158
1159 if (WARN_ON(len > skb->len))
1160 return -EINVAL;
1161
1162 nsize = skb_headlen(skb) - len;
1163 if (nsize < 0)
1164 nsize = 0;
1165
1166 /* tcp_sendmsg() can overshoot sk_wmem_queued by one full size skb.
1167 * We need some allowance to not penalize applications setting small
1168 * SO_SNDBUF values.
1169 * Also allow first and last skb in retransmit queue to be split.
1170 */
1171 limit = sk->sk_sndbuf + 2 * SKB_TRUESIZE(GSO_MAX_SIZE);
1172 if (unlikely((sk->sk_wmem_queued >> 1) > limit &&
1173 skb != tcp_rtx_queue_head(sk) &&
1174 skb != tcp_rtx_queue_tail(sk))) {
1175 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
1176 return -ENOMEM;
1177 }
1178
1179 if (skb_unclone(skb, gfp))
1180 return -ENOMEM;
1181
1182 /* Get a new skb... force flag on. */
1183 buff = sk_stream_alloc_skb(sk, nsize, gfp, true);
1184 if (!buff)
1185 return -ENOMEM; /* We'll just try again later. */
1186
1187 sk->sk_wmem_queued += buff->truesize;
1188 sk_mem_charge(sk, buff->truesize);
1189 nlen = skb->len - len - nsize;
1190 buff->truesize += nlen;
1191 skb->truesize -= nlen;
1192
1193 /* Correct the sequence numbers. */
1194 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1195 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1196 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1197
1198 /* PSH and FIN should only be set in the second packet. */
1199 flags = TCP_SKB_CB(skb)->tcp_flags;
1200 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1201 TCP_SKB_CB(buff)->tcp_flags = flags;
1202 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
1203
1204 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
1205 /* Copy and checksum data tail into the new buffer. */
1206 buff->csum = csum_partial_copy_nocheck(skb->data + len,
1207 skb_put(buff, nsize),
1208 nsize, 0);
1209
1210 skb_trim(skb, len);
1211
1212 skb->csum = csum_block_sub(skb->csum, buff->csum, len);
1213 } else {
1214 skb->ip_summed = CHECKSUM_PARTIAL;
1215 skb_split(skb, buff, len);
1216 }
1217
1218 buff->ip_summed = skb->ip_summed;
1219
1220 buff->tstamp = skb->tstamp;
1221 tcp_fragment_tstamp(skb, buff);
1222
1223 old_factor = tcp_skb_pcount(skb);
1224
1225 /* Fix up tso_factor for both original and new SKB. */
1226 tcp_set_skb_tso_segs(skb, mss_now);
1227 tcp_set_skb_tso_segs(buff, mss_now);
1228
1229 /* If this packet has been sent out already, we must
1230 * adjust the various packet counters.
1231 */
1232 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) {
1233 int diff = old_factor - tcp_skb_pcount(skb) -
1234 tcp_skb_pcount(buff);
1235
1236 if (diff)
1237 tcp_adjust_pcount(sk, skb, diff);
1238 }
1239
1240 /* Link BUFF into the send queue. */
1241 __skb_header_release(buff);
1242 tcp_insert_write_queue_after(skb, buff, sk);
1243
1244 return 0;
1245 }
1246
1247 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c
1248 * eventually). The difference is that pulled data not copied, but
1249 * immediately discarded.
1250 */
__pskb_trim_head(struct sk_buff * skb,int len)1251 static int __pskb_trim_head(struct sk_buff *skb, int len)
1252 {
1253 struct skb_shared_info *shinfo;
1254 int i, k, eat;
1255
1256 eat = min_t(int, len, skb_headlen(skb));
1257 if (eat) {
1258 __skb_pull(skb, eat);
1259 len -= eat;
1260 if (!len)
1261 return 0;
1262 }
1263 eat = len;
1264 k = 0;
1265 shinfo = skb_shinfo(skb);
1266 for (i = 0; i < shinfo->nr_frags; i++) {
1267 int size = skb_frag_size(&shinfo->frags[i]);
1268
1269 if (size <= eat) {
1270 skb_frag_unref(skb, i);
1271 eat -= size;
1272 } else {
1273 shinfo->frags[k] = shinfo->frags[i];
1274 if (eat) {
1275 shinfo->frags[k].page_offset += eat;
1276 skb_frag_size_sub(&shinfo->frags[k], eat);
1277 eat = 0;
1278 }
1279 k++;
1280 }
1281 }
1282 shinfo->nr_frags = k;
1283
1284 skb_reset_tail_pointer(skb);
1285 skb->data_len -= len;
1286 skb->len = skb->data_len;
1287 return len;
1288 }
1289
1290 /* Remove acked data from a packet in the transmit queue. */
tcp_trim_head(struct sock * sk,struct sk_buff * skb,u32 len)1291 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
1292 {
1293 u32 delta_truesize;
1294
1295 if (skb_unclone(skb, GFP_ATOMIC))
1296 return -ENOMEM;
1297
1298 delta_truesize = __pskb_trim_head(skb, len);
1299
1300 TCP_SKB_CB(skb)->seq += len;
1301 skb->ip_summed = CHECKSUM_PARTIAL;
1302
1303 if (delta_truesize) {
1304 skb->truesize -= delta_truesize;
1305 sk->sk_wmem_queued -= delta_truesize;
1306 sk_mem_uncharge(sk, delta_truesize);
1307 sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
1308 }
1309
1310 /* Any change of skb->len requires recalculation of tso factor. */
1311 if (tcp_skb_pcount(skb) > 1)
1312 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb));
1313
1314 return 0;
1315 }
1316
1317 /* Calculate MSS not accounting any TCP options. */
__tcp_mtu_to_mss(struct sock * sk,int pmtu)1318 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu)
1319 {
1320 const struct tcp_sock *tp = tcp_sk(sk);
1321 const struct inet_connection_sock *icsk = inet_csk(sk);
1322 int mss_now;
1323
1324 /* Calculate base mss without TCP options:
1325 It is MMS_S - sizeof(tcphdr) of rfc1122
1326 */
1327 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
1328
1329 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1330 if (icsk->icsk_af_ops->net_frag_header_len) {
1331 const struct dst_entry *dst = __sk_dst_get(sk);
1332
1333 if (dst && dst_allfrag(dst))
1334 mss_now -= icsk->icsk_af_ops->net_frag_header_len;
1335 }
1336
1337 /* Clamp it (mss_clamp does not include tcp options) */
1338 if (mss_now > tp->rx_opt.mss_clamp)
1339 mss_now = tp->rx_opt.mss_clamp;
1340
1341 /* Now subtract optional transport overhead */
1342 mss_now -= icsk->icsk_ext_hdr_len;
1343
1344 /* Then reserve room for full set of TCP options and 8 bytes of data */
1345 mss_now = max(mss_now, sock_net(sk)->ipv4.sysctl_tcp_min_snd_mss);
1346 return mss_now;
1347 }
1348
1349 /* Calculate MSS. Not accounting for SACKs here. */
tcp_mtu_to_mss(struct sock * sk,int pmtu)1350 int tcp_mtu_to_mss(struct sock *sk, int pmtu)
1351 {
1352 /* Subtract TCP options size, not including SACKs */
1353 return __tcp_mtu_to_mss(sk, pmtu) -
1354 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr));
1355 }
1356 EXPORT_SYMBOL(tcp_mtu_to_mss);
1357
1358 /* Inverse of above */
tcp_mss_to_mtu(struct sock * sk,int mss)1359 int tcp_mss_to_mtu(struct sock *sk, int mss)
1360 {
1361 const struct tcp_sock *tp = tcp_sk(sk);
1362 const struct inet_connection_sock *icsk = inet_csk(sk);
1363 int mtu;
1364
1365 mtu = mss +
1366 tp->tcp_header_len +
1367 icsk->icsk_ext_hdr_len +
1368 icsk->icsk_af_ops->net_header_len;
1369
1370 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
1371 if (icsk->icsk_af_ops->net_frag_header_len) {
1372 const struct dst_entry *dst = __sk_dst_get(sk);
1373
1374 if (dst && dst_allfrag(dst))
1375 mtu += icsk->icsk_af_ops->net_frag_header_len;
1376 }
1377 return mtu;
1378 }
1379
1380 /* MTU probing init per socket */
tcp_mtup_init(struct sock * sk)1381 void tcp_mtup_init(struct sock *sk)
1382 {
1383 struct tcp_sock *tp = tcp_sk(sk);
1384 struct inet_connection_sock *icsk = inet_csk(sk);
1385 struct net *net = sock_net(sk);
1386
1387 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1;
1388 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) +
1389 icsk->icsk_af_ops->net_header_len;
1390 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss);
1391 icsk->icsk_mtup.probe_size = 0;
1392 if (icsk->icsk_mtup.enabled)
1393 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1394 }
1395 EXPORT_SYMBOL(tcp_mtup_init);
1396
1397 /* This function synchronize snd mss to current pmtu/exthdr set.
1398
1399 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts
1400 for TCP options, but includes only bare TCP header.
1401
1402 tp->rx_opt.mss_clamp is mss negotiated at connection setup.
1403 It is minimum of user_mss and mss received with SYN.
1404 It also does not include TCP options.
1405
1406 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function.
1407
1408 tp->mss_cache is current effective sending mss, including
1409 all tcp options except for SACKs. It is evaluated,
1410 taking into account current pmtu, but never exceeds
1411 tp->rx_opt.mss_clamp.
1412
1413 NOTE1. rfc1122 clearly states that advertised MSS
1414 DOES NOT include either tcp or ip options.
1415
1416 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache
1417 are READ ONLY outside this function. --ANK (980731)
1418 */
tcp_sync_mss(struct sock * sk,u32 pmtu)1419 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu)
1420 {
1421 struct tcp_sock *tp = tcp_sk(sk);
1422 struct inet_connection_sock *icsk = inet_csk(sk);
1423 int mss_now;
1424
1425 if (icsk->icsk_mtup.search_high > pmtu)
1426 icsk->icsk_mtup.search_high = pmtu;
1427
1428 mss_now = tcp_mtu_to_mss(sk, pmtu);
1429 mss_now = tcp_bound_to_half_wnd(tp, mss_now);
1430
1431 /* And store cached results */
1432 icsk->icsk_pmtu_cookie = pmtu;
1433 if (icsk->icsk_mtup.enabled)
1434 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low));
1435 tp->mss_cache = mss_now;
1436
1437 return mss_now;
1438 }
1439 EXPORT_SYMBOL(tcp_sync_mss);
1440
1441 /* Compute the current effective MSS, taking SACKs and IP options,
1442 * and even PMTU discovery events into account.
1443 */
tcp_current_mss(struct sock * sk)1444 unsigned int tcp_current_mss(struct sock *sk)
1445 {
1446 const struct tcp_sock *tp = tcp_sk(sk);
1447 const struct dst_entry *dst = __sk_dst_get(sk);
1448 u32 mss_now;
1449 unsigned int header_len;
1450 struct tcp_out_options opts;
1451 struct tcp_md5sig_key *md5;
1452
1453 mss_now = tp->mss_cache;
1454
1455 if (dst) {
1456 u32 mtu = dst_mtu(dst);
1457 if (mtu != inet_csk(sk)->icsk_pmtu_cookie)
1458 mss_now = tcp_sync_mss(sk, mtu);
1459 }
1460
1461 header_len = tcp_established_options(sk, NULL, &opts, &md5) +
1462 sizeof(struct tcphdr);
1463 /* The mss_cache is sized based on tp->tcp_header_len, which assumes
1464 * some common options. If this is an odd packet (because we have SACK
1465 * blocks etc) then our calculated header_len will be different, and
1466 * we have to adjust mss_now correspondingly */
1467 if (header_len != tp->tcp_header_len) {
1468 int delta = (int) header_len - tp->tcp_header_len;
1469 mss_now -= delta;
1470 }
1471
1472 return mss_now;
1473 }
1474
1475 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
1476 * As additional protections, we do not touch cwnd in retransmission phases,
1477 * and if application hit its sndbuf limit recently.
1478 */
tcp_cwnd_application_limited(struct sock * sk)1479 static void tcp_cwnd_application_limited(struct sock *sk)
1480 {
1481 struct tcp_sock *tp = tcp_sk(sk);
1482
1483 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
1484 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
1485 /* Limited by application or receiver window. */
1486 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
1487 u32 win_used = max(tp->snd_cwnd_used, init_win);
1488 if (win_used < tp->snd_cwnd) {
1489 tp->snd_ssthresh = tcp_current_ssthresh(sk);
1490 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
1491 }
1492 tp->snd_cwnd_used = 0;
1493 }
1494 tp->snd_cwnd_stamp = tcp_time_stamp;
1495 }
1496
tcp_cwnd_validate(struct sock * sk,bool is_cwnd_limited)1497 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
1498 {
1499 struct tcp_sock *tp = tcp_sk(sk);
1500
1501 /* Track the maximum number of outstanding packets in each
1502 * window, and remember whether we were cwnd-limited then.
1503 */
1504 if (!before(tp->snd_una, tp->max_packets_seq) ||
1505 tp->packets_out > tp->max_packets_out ||
1506 is_cwnd_limited) {
1507 tp->max_packets_out = tp->packets_out;
1508 tp->max_packets_seq = tp->snd_nxt;
1509 tp->is_cwnd_limited = is_cwnd_limited;
1510 }
1511
1512 if (tcp_is_cwnd_limited(sk)) {
1513 /* Network is feed fully. */
1514 tp->snd_cwnd_used = 0;
1515 tp->snd_cwnd_stamp = tcp_time_stamp;
1516 } else {
1517 /* Network starves. */
1518 if (tp->packets_out > tp->snd_cwnd_used)
1519 tp->snd_cwnd_used = tp->packets_out;
1520
1521 if (sysctl_tcp_slow_start_after_idle &&
1522 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
1523 tcp_cwnd_application_limited(sk);
1524 }
1525 }
1526
1527 /* Minshall's variant of the Nagle send check. */
tcp_minshall_check(const struct tcp_sock * tp)1528 static bool tcp_minshall_check(const struct tcp_sock *tp)
1529 {
1530 return after(tp->snd_sml, tp->snd_una) &&
1531 !after(tp->snd_sml, tp->snd_nxt);
1532 }
1533
1534 /* Update snd_sml if this skb is under mss
1535 * Note that a TSO packet might end with a sub-mss segment
1536 * The test is really :
1537 * if ((skb->len % mss) != 0)
1538 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1539 * But we can avoid doing the divide again given we already have
1540 * skb_pcount = skb->len / mss_now
1541 */
tcp_minshall_update(struct tcp_sock * tp,unsigned int mss_now,const struct sk_buff * skb)1542 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now,
1543 const struct sk_buff *skb)
1544 {
1545 if (skb->len < tcp_skb_pcount(skb) * mss_now)
1546 tp->snd_sml = TCP_SKB_CB(skb)->end_seq;
1547 }
1548
1549 /* Return false, if packet can be sent now without violation Nagle's rules:
1550 * 1. It is full sized. (provided by caller in %partial bool)
1551 * 2. Or it contains FIN. (already checked by caller)
1552 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set.
1553 * 4. Or TCP_CORK is not set, and all sent packets are ACKed.
1554 * With Minshall's modification: all sent small packets are ACKed.
1555 */
tcp_nagle_check(bool partial,const struct tcp_sock * tp,int nonagle)1556 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
1557 int nonagle)
1558 {
1559 return partial &&
1560 ((nonagle & TCP_NAGLE_CORK) ||
1561 (!nonagle && tp->packets_out && tcp_minshall_check(tp)));
1562 }
1563
1564 /* Return how many segs we'd like on a TSO packet,
1565 * to send one TSO packet per ms
1566 */
tcp_tso_autosize(const struct sock * sk,unsigned int mss_now)1567 static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now)
1568 {
1569 u32 bytes, segs;
1570
1571 bytes = min(sk->sk_pacing_rate >> 10,
1572 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER);
1573
1574 /* Goal is to send at least one packet per ms,
1575 * not one big TSO packet every 100 ms.
1576 * This preserves ACK clocking and is consistent
1577 * with tcp_tso_should_defer() heuristic.
1578 */
1579 segs = max_t(u32, bytes / mss_now, sysctl_tcp_min_tso_segs);
1580
1581 return min_t(u32, segs, sk->sk_gso_max_segs);
1582 }
1583
1584 /* Returns the portion of skb which can be sent right away */
tcp_mss_split_point(const struct sock * sk,const struct sk_buff * skb,unsigned int mss_now,unsigned int max_segs,int nonagle)1585 static unsigned int tcp_mss_split_point(const struct sock *sk,
1586 const struct sk_buff *skb,
1587 unsigned int mss_now,
1588 unsigned int max_segs,
1589 int nonagle)
1590 {
1591 const struct tcp_sock *tp = tcp_sk(sk);
1592 u32 partial, needed, window, max_len;
1593
1594 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1595 max_len = mss_now * max_segs;
1596
1597 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
1598 return max_len;
1599
1600 needed = min(skb->len, window);
1601
1602 if (max_len <= needed)
1603 return max_len;
1604
1605 partial = needed % mss_now;
1606 /* If last segment is not a full MSS, check if Nagle rules allow us
1607 * to include this last segment in this skb.
1608 * Otherwise, we'll split the skb at last MSS boundary
1609 */
1610 if (tcp_nagle_check(partial != 0, tp, nonagle))
1611 return needed - partial;
1612
1613 return needed;
1614 }
1615
1616 /* Can at least one segment of SKB be sent right now, according to the
1617 * congestion window rules? If so, return how many segments are allowed.
1618 */
tcp_cwnd_test(const struct tcp_sock * tp,const struct sk_buff * skb)1619 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp,
1620 const struct sk_buff *skb)
1621 {
1622 u32 in_flight, cwnd, halfcwnd;
1623
1624 /* Don't be strict about the congestion window for the final FIN. */
1625 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) &&
1626 tcp_skb_pcount(skb) == 1)
1627 return 1;
1628
1629 in_flight = tcp_packets_in_flight(tp);
1630 cwnd = tp->snd_cwnd;
1631 if (in_flight >= cwnd)
1632 return 0;
1633
1634 /* For better scheduling, ensure we have at least
1635 * 2 GSO packets in flight.
1636 */
1637 halfcwnd = max(cwnd >> 1, 1U);
1638 return min(halfcwnd, cwnd - in_flight);
1639 }
1640
1641 /* Initialize TSO state of a skb.
1642 * This must be invoked the first time we consider transmitting
1643 * SKB onto the wire.
1644 */
tcp_init_tso_segs(struct sk_buff * skb,unsigned int mss_now)1645 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
1646 {
1647 int tso_segs = tcp_skb_pcount(skb);
1648
1649 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
1650 tcp_set_skb_tso_segs(skb, mss_now);
1651 tso_segs = tcp_skb_pcount(skb);
1652 }
1653 return tso_segs;
1654 }
1655
1656
1657 /* Return true if the Nagle test allows this packet to be
1658 * sent now.
1659 */
tcp_nagle_test(const struct tcp_sock * tp,const struct sk_buff * skb,unsigned int cur_mss,int nonagle)1660 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb,
1661 unsigned int cur_mss, int nonagle)
1662 {
1663 /* Nagle rule does not apply to frames, which sit in the middle of the
1664 * write_queue (they have no chances to get new data).
1665 *
1666 * This is implemented in the callers, where they modify the 'nonagle'
1667 * argument based upon the location of SKB in the send queue.
1668 */
1669 if (nonagle & TCP_NAGLE_PUSH)
1670 return true;
1671
1672 /* Don't use the nagle rule for urgent data (or for the final FIN). */
1673 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))
1674 return true;
1675
1676 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle))
1677 return true;
1678
1679 return false;
1680 }
1681
1682 /* Does at least the first segment of SKB fit into the send window? */
tcp_snd_wnd_test(const struct tcp_sock * tp,const struct sk_buff * skb,unsigned int cur_mss)1683 static bool tcp_snd_wnd_test(const struct tcp_sock *tp,
1684 const struct sk_buff *skb,
1685 unsigned int cur_mss)
1686 {
1687 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
1688
1689 if (skb->len > cur_mss)
1690 end_seq = TCP_SKB_CB(skb)->seq + cur_mss;
1691
1692 return !after(end_seq, tcp_wnd_end(tp));
1693 }
1694
1695 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk))
1696 * should be put on the wire right now. If so, it returns the number of
1697 * packets allowed by the congestion window.
1698 */
tcp_snd_test(const struct sock * sk,struct sk_buff * skb,unsigned int cur_mss,int nonagle)1699 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb,
1700 unsigned int cur_mss, int nonagle)
1701 {
1702 const struct tcp_sock *tp = tcp_sk(sk);
1703 unsigned int cwnd_quota;
1704
1705 tcp_init_tso_segs(skb, cur_mss);
1706
1707 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle))
1708 return 0;
1709
1710 cwnd_quota = tcp_cwnd_test(tp, skb);
1711 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss))
1712 cwnd_quota = 0;
1713
1714 return cwnd_quota;
1715 }
1716
1717 /* Test if sending is allowed right now. */
tcp_may_send_now(struct sock * sk)1718 bool tcp_may_send_now(struct sock *sk)
1719 {
1720 const struct tcp_sock *tp = tcp_sk(sk);
1721 struct sk_buff *skb = tcp_send_head(sk);
1722
1723 return skb &&
1724 tcp_snd_test(sk, skb, tcp_current_mss(sk),
1725 (tcp_skb_is_last(sk, skb) ?
1726 tp->nonagle : TCP_NAGLE_PUSH));
1727 }
1728
1729 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet
1730 * which is put after SKB on the list. It is very much like
1731 * tcp_fragment() except that it may make several kinds of assumptions
1732 * in order to speed up the splitting operation. In particular, we
1733 * know that all the data is in scatter-gather pages, and that the
1734 * packet has never been sent out before (and thus is not cloned).
1735 */
tso_fragment(struct sock * sk,struct sk_buff * skb,unsigned int len,unsigned int mss_now,gfp_t gfp)1736 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
1737 unsigned int mss_now, gfp_t gfp)
1738 {
1739 struct sk_buff *buff;
1740 int nlen = skb->len - len;
1741 u8 flags;
1742
1743 /* All of a TSO frame must be composed of paged data. */
1744 if (skb->len != skb->data_len)
1745 return tcp_fragment(sk, skb, len, mss_now, gfp);
1746
1747 buff = sk_stream_alloc_skb(sk, 0, gfp, true);
1748 if (unlikely(!buff))
1749 return -ENOMEM;
1750
1751 sk->sk_wmem_queued += buff->truesize;
1752 sk_mem_charge(sk, buff->truesize);
1753 buff->truesize += nlen;
1754 skb->truesize -= nlen;
1755
1756 /* Correct the sequence numbers. */
1757 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len;
1758 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq;
1759 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq;
1760
1761 /* PSH and FIN should only be set in the second packet. */
1762 flags = TCP_SKB_CB(skb)->tcp_flags;
1763 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH);
1764 TCP_SKB_CB(buff)->tcp_flags = flags;
1765
1766 /* This packet was never sent out yet, so no SACK bits. */
1767 TCP_SKB_CB(buff)->sacked = 0;
1768
1769 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
1770 skb_split(skb, buff, len);
1771 tcp_fragment_tstamp(skb, buff);
1772
1773 /* Fix up tso_factor for both original and new SKB. */
1774 tcp_set_skb_tso_segs(skb, mss_now);
1775 tcp_set_skb_tso_segs(buff, mss_now);
1776
1777 /* Link BUFF into the send queue. */
1778 __skb_header_release(buff);
1779 tcp_insert_write_queue_after(skb, buff, sk);
1780
1781 return 0;
1782 }
1783
1784 /* Try to defer sending, if possible, in order to minimize the amount
1785 * of TSO splitting we do. View it as a kind of TSO Nagle test.
1786 *
1787 * This algorithm is from John Heffner.
1788 */
tcp_tso_should_defer(struct sock * sk,struct sk_buff * skb,bool * is_cwnd_limited,u32 max_segs)1789 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb,
1790 bool *is_cwnd_limited, u32 max_segs)
1791 {
1792 const struct inet_connection_sock *icsk = inet_csk(sk);
1793 u32 age, send_win, cong_win, limit, in_flight;
1794 struct tcp_sock *tp = tcp_sk(sk);
1795 struct skb_mstamp now;
1796 struct sk_buff *head;
1797 int win_divisor;
1798
1799 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
1800 goto send_now;
1801
1802 if (icsk->icsk_ca_state >= TCP_CA_Recovery)
1803 goto send_now;
1804
1805 /* Avoid bursty behavior by allowing defer
1806 * only if the last write was recent.
1807 */
1808 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0)
1809 goto send_now;
1810
1811 in_flight = tcp_packets_in_flight(tp);
1812
1813 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight));
1814
1815 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
1816
1817 /* From in_flight test above, we know that cwnd > in_flight. */
1818 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
1819
1820 limit = min(send_win, cong_win);
1821
1822 /* If a full-sized TSO skb can be sent, do it. */
1823 if (limit >= max_segs * tp->mss_cache)
1824 goto send_now;
1825
1826 /* Middle in queue won't get any more data, full sendable already? */
1827 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len))
1828 goto send_now;
1829
1830 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor);
1831 if (win_divisor) {
1832 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
1833
1834 /* If at least some fraction of a window is available,
1835 * just use it.
1836 */
1837 chunk /= win_divisor;
1838 if (limit >= chunk)
1839 goto send_now;
1840 } else {
1841 /* Different approach, try not to defer past a single
1842 * ACK. Receiver should ACK every other full sized
1843 * frame, so if we have space for more than 3 frames
1844 * then send now.
1845 */
1846 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
1847 goto send_now;
1848 }
1849
1850 head = tcp_write_queue_head(sk);
1851 skb_mstamp_get(&now);
1852 age = skb_mstamp_us_delta(&now, &head->skb_mstamp);
1853 /* If next ACK is likely to come too late (half srtt), do not defer */
1854 if (age < (tp->srtt_us >> 4))
1855 goto send_now;
1856
1857 /* Ok, it looks like it is advisable to defer. */
1858
1859 if (cong_win < send_win && cong_win <= skb->len)
1860 *is_cwnd_limited = true;
1861
1862 return true;
1863
1864 send_now:
1865 return false;
1866 }
1867
tcp_mtu_check_reprobe(struct sock * sk)1868 static inline void tcp_mtu_check_reprobe(struct sock *sk)
1869 {
1870 struct inet_connection_sock *icsk = inet_csk(sk);
1871 struct tcp_sock *tp = tcp_sk(sk);
1872 struct net *net = sock_net(sk);
1873 u32 interval;
1874 s32 delta;
1875
1876 interval = net->ipv4.sysctl_tcp_probe_interval;
1877 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp;
1878 if (unlikely(delta >= interval * HZ)) {
1879 int mss = tcp_current_mss(sk);
1880
1881 /* Update current search range */
1882 icsk->icsk_mtup.probe_size = 0;
1883 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp +
1884 sizeof(struct tcphdr) +
1885 icsk->icsk_af_ops->net_header_len;
1886 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
1887
1888 /* Update probe time stamp */
1889 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
1890 }
1891 }
1892
1893 /* Create a new MTU probe if we are ready.
1894 * MTU probe is regularly attempting to increase the path MTU by
1895 * deliberately sending larger packets. This discovers routing
1896 * changes resulting in larger path MTUs.
1897 *
1898 * Returns 0 if we should wait to probe (no cwnd available),
1899 * 1 if a probe was sent,
1900 * -1 otherwise
1901 */
tcp_mtu_probe(struct sock * sk)1902 static int tcp_mtu_probe(struct sock *sk)
1903 {
1904 struct tcp_sock *tp = tcp_sk(sk);
1905 struct inet_connection_sock *icsk = inet_csk(sk);
1906 struct sk_buff *skb, *nskb, *next;
1907 struct net *net = sock_net(sk);
1908 int len;
1909 int probe_size;
1910 int size_needed;
1911 int copy;
1912 int mss_now;
1913 int interval;
1914
1915 /* Not currently probing/verifying,
1916 * not in recovery,
1917 * have enough cwnd, and
1918 * not SACKing (the variable headers throw things off) */
1919 if (!icsk->icsk_mtup.enabled ||
1920 icsk->icsk_mtup.probe_size ||
1921 inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
1922 tp->snd_cwnd < 11 ||
1923 tp->rx_opt.num_sacks || tp->rx_opt.dsack)
1924 return -1;
1925
1926 /* Use binary search for probe_size between tcp_mss_base,
1927 * and current mss_clamp. if (search_high - search_low)
1928 * smaller than a threshold, backoff from probing.
1929 */
1930 mss_now = tcp_current_mss(sk);
1931 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high +
1932 icsk->icsk_mtup.search_low) >> 1);
1933 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache;
1934 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low;
1935 /* When misfortune happens, we are reprobing actively,
1936 * and then reprobe timer has expired. We stick with current
1937 * probing process by not resetting search range to its orignal.
1938 */
1939 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) ||
1940 interval < net->ipv4.sysctl_tcp_probe_threshold) {
1941 /* Check whether enough time has elaplased for
1942 * another round of probing.
1943 */
1944 tcp_mtu_check_reprobe(sk);
1945 return -1;
1946 }
1947
1948 /* Have enough data in the send queue to probe? */
1949 if (tp->write_seq - tp->snd_nxt < size_needed)
1950 return -1;
1951
1952 if (tp->snd_wnd < size_needed)
1953 return -1;
1954 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp)))
1955 return 0;
1956
1957 /* Do we need to wait to drain cwnd? With none in flight, don't stall */
1958 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
1959 if (!tcp_packets_in_flight(tp))
1960 return -1;
1961 else
1962 return 0;
1963 }
1964
1965 /* We're allowed to probe. Build it now. */
1966 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
1967 if (!nskb)
1968 return -1;
1969 sk->sk_wmem_queued += nskb->truesize;
1970 sk_mem_charge(sk, nskb->truesize);
1971
1972 skb = tcp_send_head(sk);
1973
1974 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
1975 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;
1976 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
1977 TCP_SKB_CB(nskb)->sacked = 0;
1978 nskb->csum = 0;
1979 nskb->ip_summed = skb->ip_summed;
1980
1981 tcp_insert_write_queue_before(nskb, skb, sk);
1982 tcp_highest_sack_replace(sk, skb, nskb);
1983
1984 len = 0;
1985 tcp_for_write_queue_from_safe(skb, next, sk) {
1986 copy = min_t(int, skb->len, probe_size - len);
1987 if (nskb->ip_summed) {
1988 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
1989 } else {
1990 __wsum csum = skb_copy_and_csum_bits(skb, 0,
1991 skb_put(nskb, copy),
1992 copy, 0);
1993 nskb->csum = csum_block_add(nskb->csum, csum, len);
1994 }
1995
1996 if (skb->len <= copy) {
1997 /* We've eaten all the data from this skb.
1998 * Throw it away. */
1999 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
2000 tcp_unlink_write_queue(skb, sk);
2001 sk_wmem_free_skb(sk, skb);
2002 } else {
2003 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags &
2004 ~(TCPHDR_FIN|TCPHDR_PSH);
2005 if (!skb_shinfo(skb)->nr_frags) {
2006 skb_pull(skb, copy);
2007 if (skb->ip_summed != CHECKSUM_PARTIAL)
2008 skb->csum = csum_partial(skb->data,
2009 skb->len, 0);
2010 } else {
2011 __pskb_trim_head(skb, copy);
2012 tcp_set_skb_tso_segs(skb, mss_now);
2013 }
2014 TCP_SKB_CB(skb)->seq += copy;
2015 }
2016
2017 len += copy;
2018
2019 if (len >= probe_size)
2020 break;
2021 }
2022 tcp_init_tso_segs(nskb, nskb->len);
2023
2024 /* We're ready to send. If this fails, the probe will
2025 * be resegmented into mss-sized pieces by tcp_write_xmit().
2026 */
2027 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
2028 /* Decrement cwnd here because we are sending
2029 * effectively two packets. */
2030 tp->snd_cwnd--;
2031 tcp_event_new_data_sent(sk, nskb);
2032
2033 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
2034 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq;
2035 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq;
2036
2037 return 1;
2038 }
2039
2040 return -1;
2041 }
2042
2043 /* This routine writes packets to the network. It advances the
2044 * send_head. This happens as incoming acks open up the remote
2045 * window for us.
2046 *
2047 * LARGESEND note: !tcp_urg_mode is overkill, only frames between
2048 * snd_up-64k-mss .. snd_up cannot be large. However, taking into
2049 * account rare use of URG, this is not a big flaw.
2050 *
2051 * Send at most one packet when push_one > 0. Temporarily ignore
2052 * cwnd limit to force at most one packet out when push_one == 2.
2053
2054 * Returns true, if no segments are in flight and we have queued segments,
2055 * but cannot send anything now because of SWS or another problem.
2056 */
tcp_write_xmit(struct sock * sk,unsigned int mss_now,int nonagle,int push_one,gfp_t gfp)2057 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
2058 int push_one, gfp_t gfp)
2059 {
2060 struct tcp_sock *tp = tcp_sk(sk);
2061 struct sk_buff *skb;
2062 unsigned int tso_segs, sent_pkts;
2063 int cwnd_quota;
2064 int result;
2065 bool is_cwnd_limited = false;
2066 u32 max_segs;
2067
2068 sent_pkts = 0;
2069
2070 if (!push_one) {
2071 /* Do MTU probing. */
2072 result = tcp_mtu_probe(sk);
2073 if (!result) {
2074 return false;
2075 } else if (result > 0) {
2076 sent_pkts = 1;
2077 }
2078 }
2079
2080 max_segs = tcp_tso_autosize(sk, mss_now);
2081 while ((skb = tcp_send_head(sk))) {
2082 unsigned int limit;
2083
2084 tso_segs = tcp_init_tso_segs(skb, mss_now);
2085 BUG_ON(!tso_segs);
2086
2087 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) {
2088 /* "skb_mstamp" is used as a start point for the retransmit timer */
2089 skb_mstamp_get(&skb->skb_mstamp);
2090 goto repair; /* Skip network transmission */
2091 }
2092
2093 cwnd_quota = tcp_cwnd_test(tp, skb);
2094 if (!cwnd_quota) {
2095 if (push_one == 2)
2096 /* Force out a loss probe pkt. */
2097 cwnd_quota = 1;
2098 else
2099 break;
2100 }
2101
2102 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
2103 break;
2104
2105 if (tso_segs == 1) {
2106 if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
2107 (tcp_skb_is_last(sk, skb) ?
2108 nonagle : TCP_NAGLE_PUSH))))
2109 break;
2110 } else {
2111 if (!push_one &&
2112 tcp_tso_should_defer(sk, skb, &is_cwnd_limited,
2113 max_segs))
2114 break;
2115 }
2116
2117 limit = mss_now;
2118 if (tso_segs > 1 && !tcp_urg_mode(tp))
2119 limit = tcp_mss_split_point(sk, skb, mss_now,
2120 min_t(unsigned int,
2121 cwnd_quota,
2122 max_segs),
2123 nonagle);
2124
2125 if (skb->len > limit &&
2126 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))
2127 break;
2128
2129 /* TCP Small Queues :
2130 * Control number of packets in qdisc/devices to two packets / or ~1 ms.
2131 * This allows for :
2132 * - better RTT estimation and ACK scheduling
2133 * - faster recovery
2134 * - high rates
2135 * Alas, some drivers / subsystems require a fair amount
2136 * of queued bytes to ensure line rate.
2137 * One example is wifi aggregation (802.11 AMPDU)
2138 */
2139 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10);
2140 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes);
2141
2142 if (atomic_read(&sk->sk_wmem_alloc) > limit) {
2143 set_bit(TSQ_THROTTLED, &tp->tsq_flags);
2144 /* It is possible TX completion already happened
2145 * before we set TSQ_THROTTLED, so we must
2146 * test again the condition.
2147 */
2148 smp_mb__after_atomic();
2149 if (atomic_read(&sk->sk_wmem_alloc) > limit)
2150 break;
2151 }
2152
2153 /* Argh, we hit an empty skb(), presumably a thread
2154 * is sleeping in sendmsg()/sk_stream_wait_memory().
2155 * We do not want to send a pure-ack packet and have
2156 * a strange looking rtx queue with empty packet(s).
2157 */
2158 if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq)
2159 break;
2160
2161 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))
2162 break;
2163
2164 repair:
2165 /* Advance the send_head. This one is sent out.
2166 * This call will increment packets_out.
2167 */
2168 tcp_event_new_data_sent(sk, skb);
2169
2170 tcp_minshall_update(tp, mss_now, skb);
2171 sent_pkts += tcp_skb_pcount(skb);
2172
2173 if (push_one)
2174 break;
2175 }
2176
2177 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
2178 if (likely(sent_pkts || is_cwnd_limited))
2179 tcp_cwnd_validate(sk, is_cwnd_limited);
2180
2181 if (likely(sent_pkts)) {
2182 if (tcp_in_cwnd_reduction(sk))
2183 tp->prr_out += sent_pkts;
2184
2185 /* Send one loss probe per tail loss episode. */
2186 if (push_one != 2)
2187 tcp_schedule_loss_probe(sk);
2188 return false;
2189 }
2190 return !tp->packets_out && tcp_send_head(sk);
2191 }
2192
tcp_schedule_loss_probe(struct sock * sk)2193 bool tcp_schedule_loss_probe(struct sock *sk)
2194 {
2195 struct inet_connection_sock *icsk = inet_csk(sk);
2196 struct tcp_sock *tp = tcp_sk(sk);
2197 u32 timeout, tlp_time_stamp, rto_time_stamp;
2198 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
2199
2200 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
2201 return false;
2202 /* No consecutive loss probes. */
2203 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
2204 tcp_rearm_rto(sk);
2205 return false;
2206 }
2207 /* Don't do any loss probe on a Fast Open connection before 3WHS
2208 * finishes.
2209 */
2210 if (tp->fastopen_rsk)
2211 return false;
2212
2213 /* TLP is only scheduled when next timer event is RTO. */
2214 if (icsk->icsk_pending != ICSK_TIME_RETRANS)
2215 return false;
2216
2217 /* Schedule a loss probe in 2*RTT for SACK capable connections
2218 * in Open state, that are either limited by cwnd or application.
2219 */
2220 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
2221 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
2222 return false;
2223
2224 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
2225 tcp_send_head(sk))
2226 return false;
2227
2228 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account
2229 * for delayed ack when there's one outstanding packet. If no RTT
2230 * sample is available then probe after TCP_TIMEOUT_INIT.
2231 */
2232 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT;
2233 if (tp->packets_out == 1)
2234 timeout = max_t(u32, timeout,
2235 (rtt + (rtt >> 1) + TCP_DELACK_MAX));
2236 timeout = max_t(u32, timeout, msecs_to_jiffies(10));
2237
2238 /* If RTO is shorter, just schedule TLP in its place. */
2239 tlp_time_stamp = tcp_time_stamp + timeout;
2240 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
2241 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
2242 s32 delta = rto_time_stamp - tcp_time_stamp;
2243 if (delta > 0)
2244 timeout = delta;
2245 }
2246
2247 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout,
2248 TCP_RTO_MAX);
2249 return true;
2250 }
2251
2252 /* Thanks to skb fast clones, we can detect if a prior transmit of
2253 * a packet is still in a qdisc or driver queue.
2254 * In this case, there is very little point doing a retransmit !
2255 * Note: This is called from BH context only.
2256 */
skb_still_in_host_queue(const struct sock * sk,const struct sk_buff * skb)2257 static bool skb_still_in_host_queue(const struct sock *sk,
2258 const struct sk_buff *skb)
2259 {
2260 if (unlikely(skb_fclone_busy(sk, skb))) {
2261 NET_INC_STATS_BH(sock_net(sk),
2262 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES);
2263 return true;
2264 }
2265 return false;
2266 }
2267
2268 /* When probe timeout (PTO) fires, try send a new segment if possible, else
2269 * retransmit the last segment.
2270 */
tcp_send_loss_probe(struct sock * sk)2271 void tcp_send_loss_probe(struct sock *sk)
2272 {
2273 struct tcp_sock *tp = tcp_sk(sk);
2274 struct sk_buff *skb;
2275 int pcount;
2276 int mss = tcp_current_mss(sk);
2277
2278 /* At most one outstanding TLP */
2279 if (tp->tlp_high_seq)
2280 goto rearm_timer;
2281
2282 tp->tlp_retrans = 0;
2283 skb = tcp_send_head(sk);
2284 if (skb) {
2285 if (tcp_snd_wnd_test(tp, skb, mss)) {
2286 pcount = tp->packets_out;
2287 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
2288 if (tp->packets_out > pcount)
2289 goto probe_sent;
2290 goto rearm_timer;
2291 }
2292 skb = tcp_write_queue_prev(sk, skb);
2293 } else {
2294 skb = tcp_write_queue_tail(sk);
2295 }
2296
2297 if (unlikely(!skb)) {
2298 WARN_ONCE(tp->packets_out,
2299 "invalid inflight: %u state %u cwnd %u mss %d\n",
2300 tp->packets_out, sk->sk_state, tp->snd_cwnd, mss);
2301 inet_csk(sk)->icsk_pending = 0;
2302 return;
2303 }
2304
2305 if (skb_still_in_host_queue(sk, skb))
2306 goto rearm_timer;
2307
2308 pcount = tcp_skb_pcount(skb);
2309 if (WARN_ON(!pcount))
2310 goto rearm_timer;
2311
2312 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) {
2313 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
2314 GFP_ATOMIC)))
2315 goto rearm_timer;
2316 skb = tcp_write_queue_next(sk, skb);
2317 }
2318
2319 if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
2320 goto rearm_timer;
2321
2322 if (__tcp_retransmit_skb(sk, skb))
2323 goto rearm_timer;
2324
2325 tp->tlp_retrans = 1;
2326
2327 probe_sent:
2328 /* Record snd_nxt for loss detection. */
2329 tp->tlp_high_seq = tp->snd_nxt;
2330
2331 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSPROBES);
2332 /* Reset s.t. tcp_rearm_rto will restart timer from now */
2333 inet_csk(sk)->icsk_pending = 0;
2334 rearm_timer:
2335 tcp_rearm_rto(sk);
2336 }
2337
2338 /* Push out any pending frames which were held back due to
2339 * TCP_CORK or attempt at coalescing tiny packets.
2340 * The socket must be locked by the caller.
2341 */
__tcp_push_pending_frames(struct sock * sk,unsigned int cur_mss,int nonagle)2342 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
2343 int nonagle)
2344 {
2345 /* If we are closed, the bytes will have to remain here.
2346 * In time closedown will finish, we empty the write queue and
2347 * all will be happy.
2348 */
2349 if (unlikely(sk->sk_state == TCP_CLOSE))
2350 return;
2351
2352 if (tcp_write_xmit(sk, cur_mss, nonagle, 0,
2353 sk_gfp_atomic(sk, GFP_ATOMIC)))
2354 tcp_check_probe_timer(sk);
2355 }
2356
2357 /* Send _single_ skb sitting at the send head. This function requires
2358 * true push pending frames to setup probe timer etc.
2359 */
tcp_push_one(struct sock * sk,unsigned int mss_now)2360 void tcp_push_one(struct sock *sk, unsigned int mss_now)
2361 {
2362 struct sk_buff *skb = tcp_send_head(sk);
2363
2364 BUG_ON(!skb || skb->len < mss_now);
2365
2366 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation);
2367 }
2368
2369 /* This function returns the amount that we can raise the
2370 * usable window based on the following constraints
2371 *
2372 * 1. The window can never be shrunk once it is offered (RFC 793)
2373 * 2. We limit memory per socket
2374 *
2375 * RFC 1122:
2376 * "the suggested [SWS] avoidance algorithm for the receiver is to keep
2377 * RECV.NEXT + RCV.WIN fixed until:
2378 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)"
2379 *
2380 * i.e. don't raise the right edge of the window until you can raise
2381 * it at least MSS bytes.
2382 *
2383 * Unfortunately, the recommended algorithm breaks header prediction,
2384 * since header prediction assumes th->window stays fixed.
2385 *
2386 * Strictly speaking, keeping th->window fixed violates the receiver
2387 * side SWS prevention criteria. The problem is that under this rule
2388 * a stream of single byte packets will cause the right side of the
2389 * window to always advance by a single byte.
2390 *
2391 * Of course, if the sender implements sender side SWS prevention
2392 * then this will not be a problem.
2393 *
2394 * BSD seems to make the following compromise:
2395 *
2396 * If the free space is less than the 1/4 of the maximum
2397 * space available and the free space is less than 1/2 mss,
2398 * then set the window to 0.
2399 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ]
2400 * Otherwise, just prevent the window from shrinking
2401 * and from being larger than the largest representable value.
2402 *
2403 * This prevents incremental opening of the window in the regime
2404 * where TCP is limited by the speed of the reader side taking
2405 * data out of the TCP receive queue. It does nothing about
2406 * those cases where the window is constrained on the sender side
2407 * because the pipeline is full.
2408 *
2409 * BSD also seems to "accidentally" limit itself to windows that are a
2410 * multiple of MSS, at least until the free space gets quite small.
2411 * This would appear to be a side effect of the mbuf implementation.
2412 * Combining these two algorithms results in the observed behavior
2413 * of having a fixed window size at almost all times.
2414 *
2415 * Below we obtain similar behavior by forcing the offered window to
2416 * a multiple of the mss when it is feasible to do so.
2417 *
2418 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes.
2419 * Regular options like TIMESTAMP are taken into account.
2420 */
__tcp_select_window(struct sock * sk)2421 u32 __tcp_select_window(struct sock *sk)
2422 {
2423 struct inet_connection_sock *icsk = inet_csk(sk);
2424 struct tcp_sock *tp = tcp_sk(sk);
2425 /* MSS for the peer's data. Previous versions used mss_clamp
2426 * here. I don't know if the value based on our guesses
2427 * of peer's MSS is better for the performance. It's more correct
2428 * but may be worse for the performance because of rcv_mss
2429 * fluctuations. --SAW 1998/11/1
2430 */
2431 int mss = icsk->icsk_ack.rcv_mss;
2432 int free_space = tcp_space(sk);
2433 int allowed_space = tcp_full_space(sk);
2434 int full_space = min_t(int, tp->window_clamp, allowed_space);
2435 int window;
2436
2437 if (unlikely(mss > full_space)) {
2438 mss = full_space;
2439 if (mss <= 0)
2440 return 0;
2441 }
2442 if (free_space < (full_space >> 1)) {
2443 icsk->icsk_ack.quick = 0;
2444
2445 if (tcp_under_memory_pressure(sk))
2446 tp->rcv_ssthresh = min(tp->rcv_ssthresh,
2447 4U * tp->advmss);
2448
2449 /* free_space might become our new window, make sure we don't
2450 * increase it due to wscale.
2451 */
2452 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale);
2453
2454 /* if free space is less than mss estimate, or is below 1/16th
2455 * of the maximum allowed, try to move to zero-window, else
2456 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and
2457 * new incoming data is dropped due to memory limits.
2458 * With large window, mss test triggers way too late in order
2459 * to announce zero window in time before rmem limit kicks in.
2460 */
2461 if (free_space < (allowed_space >> 4) || free_space < mss)
2462 return 0;
2463 }
2464
2465 if (free_space > tp->rcv_ssthresh)
2466 free_space = tp->rcv_ssthresh;
2467
2468 /* Don't do rounding if we are using window scaling, since the
2469 * scaled window will not line up with the MSS boundary anyway.
2470 */
2471 window = tp->rcv_wnd;
2472 if (tp->rx_opt.rcv_wscale) {
2473 window = free_space;
2474
2475 /* Advertise enough space so that it won't get scaled away.
2476 * Import case: prevent zero window announcement if
2477 * 1<<rcv_wscale > mss.
2478 */
2479 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window)
2480 window = (((window >> tp->rx_opt.rcv_wscale) + 1)
2481 << tp->rx_opt.rcv_wscale);
2482 } else {
2483 /* Get the largest window that is a nice multiple of mss.
2484 * Window clamp already applied above.
2485 * If our current window offering is within 1 mss of the
2486 * free space we just keep it. This prevents the divide
2487 * and multiply from happening most of the time.
2488 * We also don't do any window rounding when the free space
2489 * is too small.
2490 */
2491 if (window <= free_space - mss || window > free_space)
2492 window = (free_space / mss) * mss;
2493 else if (mss == full_space &&
2494 free_space > window + (full_space >> 1))
2495 window = free_space;
2496 }
2497
2498 return window;
2499 }
2500
2501 /* Collapses two adjacent SKB's during retransmission. */
tcp_collapse_retrans(struct sock * sk,struct sk_buff * skb)2502 static void tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
2503 {
2504 struct tcp_sock *tp = tcp_sk(sk);
2505 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb);
2506 int skb_size, next_skb_size;
2507
2508 skb_size = skb->len;
2509 next_skb_size = next_skb->len;
2510
2511 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1);
2512
2513 tcp_highest_sack_replace(sk, next_skb, skb);
2514
2515 tcp_unlink_write_queue(next_skb, sk);
2516
2517 skb_copy_from_linear_data(next_skb, skb_put(skb, next_skb_size),
2518 next_skb_size);
2519
2520 if (next_skb->ip_summed == CHECKSUM_PARTIAL)
2521 skb->ip_summed = CHECKSUM_PARTIAL;
2522
2523 if (skb->ip_summed != CHECKSUM_PARTIAL)
2524 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
2525
2526 /* Update sequence range on original skb. */
2527 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;
2528
2529 /* Merge over control information. This moves PSH/FIN etc. over */
2530 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags;
2531
2532 /* All done, get rid of second SKB and account for it so
2533 * packet counting does not break.
2534 */
2535 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS;
2536
2537 /* changed transmit queue under us so clear hints */
2538 tcp_clear_retrans_hints_partial(tp);
2539 if (next_skb == tp->retransmit_skb_hint)
2540 tp->retransmit_skb_hint = skb;
2541
2542 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb));
2543
2544 sk_wmem_free_skb(sk, next_skb);
2545 }
2546
2547 /* Check if coalescing SKBs is legal. */
tcp_can_collapse(const struct sock * sk,const struct sk_buff * skb)2548 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb)
2549 {
2550 if (tcp_skb_pcount(skb) > 1)
2551 return false;
2552 /* TODO: SACK collapsing could be used to remove this condition */
2553 if (skb_shinfo(skb)->nr_frags != 0)
2554 return false;
2555 if (skb_cloned(skb))
2556 return false;
2557 if (skb == tcp_send_head(sk))
2558 return false;
2559 /* Some heurestics for collapsing over SACK'd could be invented */
2560 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
2561 return false;
2562
2563 return true;
2564 }
2565
2566 /* Collapse packets in the retransmit queue to make to create
2567 * less packets on the wire. This is only done on retransmission.
2568 */
tcp_retrans_try_collapse(struct sock * sk,struct sk_buff * to,int space)2569 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to,
2570 int space)
2571 {
2572 struct tcp_sock *tp = tcp_sk(sk);
2573 struct sk_buff *skb = to, *tmp;
2574 bool first = true;
2575
2576 if (!sysctl_tcp_retrans_collapse)
2577 return;
2578 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2579 return;
2580
2581 tcp_for_write_queue_from_safe(skb, tmp, sk) {
2582 if (!tcp_can_collapse(sk, skb))
2583 break;
2584
2585 space -= skb->len;
2586
2587 if (first) {
2588 first = false;
2589 continue;
2590 }
2591
2592 if (space < 0)
2593 break;
2594 /* Punt if not enough space exists in the first SKB for
2595 * the data in the second
2596 */
2597 if (skb->len > skb_availroom(to))
2598 break;
2599
2600 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp)))
2601 break;
2602
2603 tcp_collapse_retrans(sk, to);
2604 }
2605 }
2606
2607 /* This retransmits one SKB. Policy decisions and retransmit queue
2608 * state updates are done by the caller. Returns non-zero if an
2609 * error occurred which prevented the send.
2610 */
__tcp_retransmit_skb(struct sock * sk,struct sk_buff * skb)2611 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2612 {
2613 struct tcp_sock *tp = tcp_sk(sk);
2614 struct inet_connection_sock *icsk = inet_csk(sk);
2615 unsigned int cur_mss;
2616 int err;
2617
2618 /* Inconslusive MTU probe */
2619 if (icsk->icsk_mtup.probe_size) {
2620 icsk->icsk_mtup.probe_size = 0;
2621 }
2622
2623 /* Do not sent more than we queued. 1/4 is reserved for possible
2624 * copying overhead: fragmentation, tunneling, mangling etc.
2625 */
2626 if (atomic_read(&sk->sk_wmem_alloc) >
2627 min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
2628 sk->sk_sndbuf))
2629 return -EAGAIN;
2630
2631 if (skb_still_in_host_queue(sk, skb))
2632 return -EBUSY;
2633
2634 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
2635 if (unlikely(before(TCP_SKB_CB(skb)->end_seq, tp->snd_una))) {
2636 WARN_ON_ONCE(1);
2637 return -EINVAL;
2638 }
2639 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2640 return -ENOMEM;
2641 }
2642
2643 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
2644 return -EHOSTUNREACH; /* Routing failure or similar. */
2645
2646 cur_mss = tcp_current_mss(sk);
2647
2648 /* If receiver has shrunk his window, and skb is out of
2649 * new window, do not retransmit it. The exception is the
2650 * case, when window is shrunk to zero. In this case
2651 * our retransmit serves as a zero window probe.
2652 */
2653 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) &&
2654 TCP_SKB_CB(skb)->seq != tp->snd_una)
2655 return -EAGAIN;
2656
2657 if (skb->len > cur_mss) {
2658 if (tcp_fragment(sk, skb, cur_mss, cur_mss, GFP_ATOMIC))
2659 return -ENOMEM; /* We'll try again later. */
2660 } else {
2661 int oldpcount = tcp_skb_pcount(skb);
2662
2663 if (unlikely(oldpcount > 1)) {
2664 if (skb_unclone(skb, GFP_ATOMIC))
2665 return -ENOMEM;
2666 tcp_init_tso_segs(skb, cur_mss);
2667 tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
2668 }
2669 }
2670
2671 /* RFC3168, section 6.1.1.1. ECN fallback */
2672 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN)
2673 tcp_ecn_clear_syn(sk, skb);
2674
2675 tcp_retrans_try_collapse(sk, skb, cur_mss);
2676
2677 /* Make a copy, if the first transmission SKB clone we made
2678 * is still in somebody's hands, else make a clone.
2679 */
2680
2681 /* make sure skb->data is aligned on arches that require it
2682 * and check if ack-trimming & collapsing extended the headroom
2683 * beyond what csum_start can cover.
2684 */
2685 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) ||
2686 skb_headroom(skb) >= 0xFFFF)) {
2687 struct sk_buff *nskb;
2688
2689 skb_mstamp_get(&skb->skb_mstamp);
2690 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC);
2691 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) :
2692 -ENOBUFS;
2693 } else {
2694 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2695 }
2696
2697 if (likely(!err)) {
2698 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
2699 /* Update global TCP statistics. */
2700 TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS);
2701 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)
2702 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
2703 tp->total_retrans++;
2704 }
2705 return err;
2706 }
2707
tcp_retransmit_skb(struct sock * sk,struct sk_buff * skb)2708 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
2709 {
2710 struct tcp_sock *tp = tcp_sk(sk);
2711 int err = __tcp_retransmit_skb(sk, skb);
2712
2713 if (err == 0) {
2714 #if FASTRETRANS_DEBUG > 0
2715 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2716 net_dbg_ratelimited("retrans_out leaked\n");
2717 }
2718 #endif
2719 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS;
2720 tp->retrans_out += tcp_skb_pcount(skb);
2721
2722 /* Save stamp of the first retransmit. */
2723 if (!tp->retrans_stamp)
2724 tp->retrans_stamp = tcp_skb_timestamp(skb);
2725
2726 } else if (err != -EBUSY) {
2727 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
2728 }
2729
2730 if (tp->undo_retrans < 0)
2731 tp->undo_retrans = 0;
2732 tp->undo_retrans += tcp_skb_pcount(skb);
2733 return err;
2734 }
2735
2736 /* Check if we forward retransmits are possible in the current
2737 * window/congestion state.
2738 */
tcp_can_forward_retransmit(struct sock * sk)2739 static bool tcp_can_forward_retransmit(struct sock *sk)
2740 {
2741 const struct inet_connection_sock *icsk = inet_csk(sk);
2742 const struct tcp_sock *tp = tcp_sk(sk);
2743
2744 /* Forward retransmissions are possible only during Recovery. */
2745 if (icsk->icsk_ca_state != TCP_CA_Recovery)
2746 return false;
2747
2748 /* No forward retransmissions in Reno are possible. */
2749 if (tcp_is_reno(tp))
2750 return false;
2751
2752 /* Yeah, we have to make difficult choice between forward transmission
2753 * and retransmission... Both ways have their merits...
2754 *
2755 * For now we do not retransmit anything, while we have some new
2756 * segments to send. In the other cases, follow rule 3 for
2757 * NextSeg() specified in RFC3517.
2758 */
2759
2760 if (tcp_may_send_now(sk))
2761 return false;
2762
2763 return true;
2764 }
2765
2766 /* This gets called after a retransmit timeout, and the initially
2767 * retransmitted data is acknowledged. It tries to continue
2768 * resending the rest of the retransmit queue, until either
2769 * we've sent it all or the congestion window limit is reached.
2770 * If doing SACK, the first ACK which comes back for a timeout
2771 * based retransmit packet might feed us FACK information again.
2772 * If so, we use it to avoid unnecessarily retransmissions.
2773 */
tcp_xmit_retransmit_queue(struct sock * sk)2774 void tcp_xmit_retransmit_queue(struct sock *sk)
2775 {
2776 const struct inet_connection_sock *icsk = inet_csk(sk);
2777 struct tcp_sock *tp = tcp_sk(sk);
2778 struct sk_buff *skb;
2779 struct sk_buff *hole = NULL;
2780 u32 last_lost;
2781 int mib_idx;
2782 int fwd_rexmitting = 0;
2783
2784 if (!tp->packets_out)
2785 return;
2786
2787 if (!tp->lost_out)
2788 tp->retransmit_high = tp->snd_una;
2789
2790 if (tp->retransmit_skb_hint) {
2791 skb = tp->retransmit_skb_hint;
2792 last_lost = TCP_SKB_CB(skb)->end_seq;
2793 if (after(last_lost, tp->retransmit_high))
2794 last_lost = tp->retransmit_high;
2795 } else {
2796 skb = tcp_write_queue_head(sk);
2797 last_lost = tp->snd_una;
2798 }
2799
2800 tcp_for_write_queue_from(skb, sk) {
2801 __u8 sacked = TCP_SKB_CB(skb)->sacked;
2802
2803 if (skb == tcp_send_head(sk))
2804 break;
2805 /* we could do better than to assign each time */
2806 if (!hole)
2807 tp->retransmit_skb_hint = skb;
2808
2809 /* Assume this retransmit will generate
2810 * only one packet for congestion window
2811 * calculation purposes. This works because
2812 * tcp_retransmit_skb() will chop up the
2813 * packet to be MSS sized and all the
2814 * packet counting works out.
2815 */
2816 if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
2817 return;
2818
2819 if (fwd_rexmitting) {
2820 begin_fwd:
2821 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
2822 break;
2823 mib_idx = LINUX_MIB_TCPFORWARDRETRANS;
2824
2825 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) {
2826 tp->retransmit_high = last_lost;
2827 if (!tcp_can_forward_retransmit(sk))
2828 break;
2829 /* Backtrack if necessary to non-L'ed skb */
2830 if (hole) {
2831 skb = hole;
2832 hole = NULL;
2833 }
2834 fwd_rexmitting = 1;
2835 goto begin_fwd;
2836
2837 } else if (!(sacked & TCPCB_LOST)) {
2838 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED)))
2839 hole = skb;
2840 continue;
2841
2842 } else {
2843 last_lost = TCP_SKB_CB(skb)->end_seq;
2844 if (icsk->icsk_ca_state != TCP_CA_Loss)
2845 mib_idx = LINUX_MIB_TCPFASTRETRANS;
2846 else
2847 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS;
2848 }
2849
2850 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))
2851 continue;
2852
2853 if (tcp_retransmit_skb(sk, skb))
2854 return;
2855
2856 NET_INC_STATS_BH(sock_net(sk), mib_idx);
2857
2858 if (tcp_in_cwnd_reduction(sk))
2859 tp->prr_out += tcp_skb_pcount(skb);
2860
2861 if (skb == tcp_write_queue_head(sk))
2862 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2863 inet_csk(sk)->icsk_rto,
2864 TCP_RTO_MAX);
2865 }
2866 }
2867
2868 /* We allow to exceed memory limits for FIN packets to expedite
2869 * connection tear down and (memory) recovery.
2870 * Otherwise tcp_send_fin() could be tempted to either delay FIN
2871 * or even be forced to close flow without any FIN.
2872 * In general, we want to allow one skb per socket to avoid hangs
2873 * with edge trigger epoll()
2874 */
sk_forced_mem_schedule(struct sock * sk,int size)2875 void sk_forced_mem_schedule(struct sock *sk, int size)
2876 {
2877 int amt, status;
2878
2879 if (size <= sk->sk_forward_alloc)
2880 return;
2881 amt = sk_mem_pages(size);
2882 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
2883 sk_memory_allocated_add(sk, amt, &status);
2884 }
2885
2886 /* Send a FIN. The caller locks the socket for us.
2887 * We should try to send a FIN packet really hard, but eventually give up.
2888 */
tcp_send_fin(struct sock * sk)2889 void tcp_send_fin(struct sock *sk)
2890 {
2891 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk);
2892 struct tcp_sock *tp = tcp_sk(sk);
2893
2894 /* Optimization, tack on the FIN if we have one skb in write queue and
2895 * this skb was not yet sent, or we are under memory pressure.
2896 * Note: in the latter case, FIN packet will be sent after a timeout,
2897 * as TCP stack thinks it has already been transmitted.
2898 */
2899 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) {
2900 coalesce:
2901 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN;
2902 TCP_SKB_CB(tskb)->end_seq++;
2903 tp->write_seq++;
2904 if (!tcp_send_head(sk)) {
2905 /* This means tskb was already sent.
2906 * Pretend we included the FIN on previous transmit.
2907 * We need to set tp->snd_nxt to the value it would have
2908 * if FIN had been sent. This is because retransmit path
2909 * does not change tp->snd_nxt.
2910 */
2911 tp->snd_nxt++;
2912 return;
2913 }
2914 } else {
2915 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation);
2916 if (unlikely(!skb)) {
2917 if (tskb)
2918 goto coalesce;
2919 return;
2920 }
2921 skb_reserve(skb, MAX_TCP_HEADER);
2922 sk_forced_mem_schedule(sk, skb->truesize);
2923 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
2924 tcp_init_nondata_skb(skb, tp->write_seq,
2925 TCPHDR_ACK | TCPHDR_FIN);
2926 tcp_queue_skb(sk, skb);
2927 }
2928 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF);
2929 }
2930
2931 /* We get here when a process closes a file descriptor (either due to
2932 * an explicit close() or as a byproduct of exit()'ing) and there
2933 * was unread data in the receive queue. This behavior is recommended
2934 * by RFC 2525, section 2.17. -DaveM
2935 */
tcp_send_active_reset(struct sock * sk,gfp_t priority)2936 void tcp_send_active_reset(struct sock *sk, gfp_t priority)
2937 {
2938 struct sk_buff *skb;
2939
2940 /* NOTE: No TCP options attached and we never retransmit this. */
2941 skb = alloc_skb(MAX_TCP_HEADER, priority);
2942 if (!skb) {
2943 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2944 return;
2945 }
2946
2947 /* Reserve space for headers and prepare control bits. */
2948 skb_reserve(skb, MAX_TCP_HEADER);
2949 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
2950 TCPHDR_ACK | TCPHDR_RST);
2951 skb_mstamp_get(&skb->skb_mstamp);
2952 /* Send it off. */
2953 if (tcp_transmit_skb(sk, skb, 0, priority))
2954 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
2955
2956 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS);
2957 }
2958
2959 /* Send a crossed SYN-ACK during socket establishment.
2960 * WARNING: This routine must only be called when we have already sent
2961 * a SYN packet that crossed the incoming SYN that caused this routine
2962 * to get called. If this assumption fails then the initial rcv_wnd
2963 * and rcv_wscale values will not be correct.
2964 */
tcp_send_synack(struct sock * sk)2965 int tcp_send_synack(struct sock *sk)
2966 {
2967 struct sk_buff *skb;
2968
2969 skb = tcp_write_queue_head(sk);
2970 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
2971 pr_debug("%s: wrong queue state\n", __func__);
2972 return -EFAULT;
2973 }
2974 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) {
2975 if (skb_cloned(skb)) {
2976 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
2977 if (!nskb)
2978 return -ENOMEM;
2979 tcp_unlink_write_queue(skb, sk);
2980 __skb_header_release(nskb);
2981 __tcp_add_write_queue_head(sk, nskb);
2982 sk_wmem_free_skb(sk, skb);
2983 sk->sk_wmem_queued += nskb->truesize;
2984 sk_mem_charge(sk, nskb->truesize);
2985 skb = nskb;
2986 }
2987
2988 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK;
2989 tcp_ecn_send_synack(sk, skb);
2990 }
2991 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
2992 }
2993
2994 /**
2995 * tcp_make_synack - Prepare a SYN-ACK.
2996 * sk: listener socket
2997 * dst: dst entry attached to the SYNACK
2998 * req: request_sock pointer
2999 *
3000 * Allocate one skb and build a SYNACK packet.
3001 * @dst is consumed : Caller should not use it again.
3002 */
tcp_make_synack(const struct sock * sk,struct dst_entry * dst,struct request_sock * req,struct tcp_fastopen_cookie * foc,bool attach_req)3003 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
3004 struct request_sock *req,
3005 struct tcp_fastopen_cookie *foc,
3006 bool attach_req)
3007 {
3008 struct inet_request_sock *ireq = inet_rsk(req);
3009 const struct tcp_sock *tp = tcp_sk(sk);
3010 struct tcp_md5sig_key *md5 = NULL;
3011 struct tcp_out_options opts;
3012 struct sk_buff *skb;
3013 int tcp_header_size;
3014 struct tcphdr *th;
3015 u16 user_mss;
3016 int mss;
3017
3018 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC);
3019 if (unlikely(!skb)) {
3020 dst_release(dst);
3021 return NULL;
3022 }
3023 /* Reserve space for headers. */
3024 skb_reserve(skb, MAX_TCP_HEADER);
3025
3026 if (attach_req) {
3027 skb_set_owner_w(skb, req_to_sk(req));
3028 } else {
3029 /* sk is a const pointer, because we want to express multiple
3030 * cpu might call us concurrently.
3031 * sk->sk_wmem_alloc in an atomic, we can promote to rw.
3032 */
3033 skb_set_owner_w(skb, (struct sock *)sk);
3034 }
3035 skb_dst_set(skb, dst);
3036
3037 mss = dst_metric_advmss(dst);
3038 user_mss = READ_ONCE(tp->rx_opt.user_mss);
3039 if (user_mss && user_mss < mss)
3040 mss = user_mss;
3041
3042 memset(&opts, 0, sizeof(opts));
3043 #ifdef CONFIG_SYN_COOKIES
3044 if (unlikely(req->cookie_ts))
3045 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req);
3046 else
3047 #endif
3048 skb_mstamp_get(&skb->skb_mstamp);
3049
3050 #ifdef CONFIG_TCP_MD5SIG
3051 rcu_read_lock();
3052 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req));
3053 #endif
3054 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4);
3055 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) +
3056 sizeof(*th);
3057
3058 skb_push(skb, tcp_header_size);
3059 skb_reset_transport_header(skb);
3060
3061 th = tcp_hdr(skb);
3062 memset(th, 0, sizeof(struct tcphdr));
3063 th->syn = 1;
3064 th->ack = 1;
3065 tcp_ecn_make_synack(req, th);
3066 th->source = htons(ireq->ir_num);
3067 th->dest = ireq->ir_rmt_port;
3068 skb->ip_summed = CHECKSUM_PARTIAL;
3069 th->seq = htonl(tcp_rsk(req)->snt_isn);
3070 /* XXX data is queued and acked as is. No buffer/window check */
3071 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt);
3072
3073 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
3074 th->window = htons(min(req->rsk_rcv_wnd, 65535U));
3075 tcp_options_write((__be32 *)(th + 1), NULL, &opts);
3076 th->doff = (tcp_header_size >> 2);
3077 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);
3078
3079 #ifdef CONFIG_TCP_MD5SIG
3080 /* Okay, we have all we need - do the md5 hash if needed */
3081 if (md5)
3082 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location,
3083 md5, req_to_sk(req), skb);
3084 rcu_read_unlock();
3085 #endif
3086
3087 /* Do not fool tcpdump (if any), clean our debris */
3088 skb->tstamp.tv64 = 0;
3089 return skb;
3090 }
3091 EXPORT_SYMBOL(tcp_make_synack);
3092
tcp_ca_dst_init(struct sock * sk,const struct dst_entry * dst)3093 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst)
3094 {
3095 struct inet_connection_sock *icsk = inet_csk(sk);
3096 const struct tcp_congestion_ops *ca;
3097 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO);
3098
3099 if (ca_key == TCP_CA_UNSPEC)
3100 return;
3101
3102 rcu_read_lock();
3103 ca = tcp_ca_find_key(ca_key);
3104 if (likely(ca && try_module_get(ca->owner))) {
3105 module_put(icsk->icsk_ca_ops->owner);
3106 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst);
3107 icsk->icsk_ca_ops = ca;
3108 }
3109 rcu_read_unlock();
3110 }
3111
3112 /* Do all connect socket setups that can be done AF independent. */
tcp_connect_init(struct sock * sk)3113 static void tcp_connect_init(struct sock *sk)
3114 {
3115 const struct dst_entry *dst = __sk_dst_get(sk);
3116 struct tcp_sock *tp = tcp_sk(sk);
3117 __u8 rcv_wscale;
3118
3119 /* We'll fix this up when we get a response from the other end.
3120 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT.
3121 */
3122 tp->tcp_header_len = sizeof(struct tcphdr) +
3123 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0);
3124
3125 #ifdef CONFIG_TCP_MD5SIG
3126 if (tp->af_specific->md5_lookup(sk, sk))
3127 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED;
3128 #endif
3129
3130 /* If user gave his TCP_MAXSEG, record it to clamp */
3131 if (tp->rx_opt.user_mss)
3132 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3133 tp->max_window = 0;
3134 tcp_mtup_init(sk);
3135 tcp_sync_mss(sk, dst_mtu(dst));
3136
3137 tcp_ca_dst_init(sk, dst);
3138
3139 if (!tp->window_clamp)
3140 tp->window_clamp = dst_metric(dst, RTAX_WINDOW);
3141 tp->advmss = dst_metric_advmss(dst);
3142 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss)
3143 tp->advmss = tp->rx_opt.user_mss;
3144
3145 tcp_initialize_rcv_mss(sk);
3146
3147 /* limit the window selection if the user enforce a smaller rx buffer */
3148 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK &&
3149 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0))
3150 tp->window_clamp = tcp_full_space(sk);
3151
3152 tcp_select_initial_window(tcp_full_space(sk),
3153 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0),
3154 &tp->rcv_wnd,
3155 &tp->window_clamp,
3156 sysctl_tcp_window_scaling,
3157 &rcv_wscale,
3158 dst_metric(dst, RTAX_INITRWND));
3159
3160 tp->rx_opt.rcv_wscale = rcv_wscale;
3161 tp->rcv_ssthresh = tp->rcv_wnd;
3162
3163 sk->sk_err = 0;
3164 sock_reset_flag(sk, SOCK_DONE);
3165 tp->snd_wnd = 0;
3166 tcp_init_wl(tp, 0);
3167 tcp_write_queue_purge(sk);
3168 tp->snd_una = tp->write_seq;
3169 tp->snd_sml = tp->write_seq;
3170 tp->snd_up = tp->write_seq;
3171 tp->snd_nxt = tp->write_seq;
3172
3173 if (likely(!tp->repair))
3174 tp->rcv_nxt = 0;
3175 else
3176 tp->rcv_tstamp = tcp_time_stamp;
3177 tp->rcv_wup = tp->rcv_nxt;
3178 tp->copied_seq = tp->rcv_nxt;
3179
3180 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
3181 inet_csk(sk)->icsk_retransmits = 0;
3182 tcp_clear_retrans(tp);
3183 }
3184
tcp_connect_queue_skb(struct sock * sk,struct sk_buff * skb)3185 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
3186 {
3187 struct tcp_sock *tp = tcp_sk(sk);
3188 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
3189
3190 tcb->end_seq += skb->len;
3191 __skb_header_release(skb);
3192 __tcp_add_write_queue_tail(sk, skb);
3193 sk->sk_wmem_queued += skb->truesize;
3194 sk_mem_charge(sk, skb->truesize);
3195 tp->write_seq = tcb->end_seq;
3196 tp->packets_out += tcp_skb_pcount(skb);
3197 }
3198
3199 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
3200 * queue a data-only packet after the regular SYN, such that regular SYNs
3201 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges
3202 * only the SYN sequence, the data are retransmitted in the first ACK.
3203 * If cookie is not cached or other error occurs, falls back to send a
3204 * regular SYN with Fast Open cookie request option.
3205 */
tcp_send_syn_data(struct sock * sk,struct sk_buff * syn)3206 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
3207 {
3208 struct tcp_sock *tp = tcp_sk(sk);
3209 struct tcp_fastopen_request *fo = tp->fastopen_req;
3210 int syn_loss = 0, space, err = 0;
3211 unsigned long last_syn_loss = 0;
3212 struct sk_buff *syn_data;
3213
3214 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */
3215 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie,
3216 &syn_loss, &last_syn_loss);
3217 /* Recurring FO SYN losses: revert to regular handshake temporarily */
3218 if (syn_loss > 1 &&
3219 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) {
3220 fo->cookie.len = -1;
3221 goto fallback;
3222 }
3223
3224 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE)
3225 fo->cookie.len = -1;
3226 else if (fo->cookie.len <= 0)
3227 goto fallback;
3228
3229 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and
3230 * user-MSS. Reserve maximum option space for middleboxes that add
3231 * private TCP options. The cost is reduced data space in SYN :(
3232 */
3233 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp)
3234 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
3235 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) -
3236 MAX_TCP_OPTION_SPACE;
3237
3238 space = min_t(size_t, space, fo->size);
3239
3240 /* limit to order-0 allocations */
3241 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER));
3242
3243 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false);
3244 if (!syn_data)
3245 goto fallback;
3246 syn_data->ip_summed = CHECKSUM_PARTIAL;
3247 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb));
3248 if (space) {
3249 int copied = copy_from_iter(skb_put(syn_data, space), space,
3250 &fo->data->msg_iter);
3251 if (unlikely(!copied)) {
3252 kfree_skb(syn_data);
3253 goto fallback;
3254 }
3255 if (copied != space) {
3256 skb_trim(syn_data, copied);
3257 space = copied;
3258 }
3259 }
3260 /* No more data pending in inet_wait_for_connect() */
3261 if (space == fo->size)
3262 fo->data = NULL;
3263 fo->copied = space;
3264
3265 tcp_connect_queue_skb(sk, syn_data);
3266
3267 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation);
3268
3269 syn->skb_mstamp = syn_data->skb_mstamp;
3270
3271 /* Now full SYN+DATA was cloned and sent (or not),
3272 * remove the SYN from the original skb (syn_data)
3273 * we keep in write queue in case of a retransmit, as we
3274 * also have the SYN packet (with no data) in the same queue.
3275 */
3276 TCP_SKB_CB(syn_data)->seq++;
3277 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH;
3278 if (!err) {
3279 tp->syn_data = (fo->copied > 0);
3280 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT);
3281 goto done;
3282 }
3283
3284 fallback:
3285 /* Send a regular SYN with Fast Open cookie request option */
3286 if (fo->cookie.len > 0)
3287 fo->cookie.len = 0;
3288 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation);
3289 if (err)
3290 tp->syn_fastopen = 0;
3291 done:
3292 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */
3293 return err;
3294 }
3295
3296 /* Build a SYN and send it off. */
tcp_connect(struct sock * sk)3297 int tcp_connect(struct sock *sk)
3298 {
3299 struct tcp_sock *tp = tcp_sk(sk);
3300 struct sk_buff *buff;
3301 int err;
3302
3303 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
3304 return -EHOSTUNREACH; /* Routing failure or similar. */
3305
3306 tcp_connect_init(sk);
3307
3308 if (unlikely(tp->repair)) {
3309 tcp_finish_connect(sk, NULL);
3310 return 0;
3311 }
3312
3313 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true);
3314 if (unlikely(!buff))
3315 return -ENOBUFS;
3316
3317 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN);
3318 tp->retrans_stamp = tcp_time_stamp;
3319 tcp_connect_queue_skb(sk, buff);
3320 tcp_ecn_send_syn(sk, buff);
3321
3322 /* Send off SYN; include data in Fast Open. */
3323 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) :
3324 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation);
3325 if (err == -ECONNREFUSED)
3326 return err;
3327
3328 /* We change tp->snd_nxt after the tcp_transmit_skb() call
3329 * in order to make this packet get counted in tcpOutSegs.
3330 */
3331 tp->snd_nxt = tp->write_seq;
3332 tp->pushed_seq = tp->write_seq;
3333 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS);
3334
3335 /* Timer for repeating the SYN until an answer. */
3336 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3337 inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3338 return 0;
3339 }
3340 EXPORT_SYMBOL(tcp_connect);
3341
3342 /* Send out a delayed ack, the caller does the policy checking
3343 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check()
3344 * for details.
3345 */
tcp_send_delayed_ack(struct sock * sk)3346 void tcp_send_delayed_ack(struct sock *sk)
3347 {
3348 struct inet_connection_sock *icsk = inet_csk(sk);
3349 int ato = icsk->icsk_ack.ato;
3350 unsigned long timeout;
3351
3352 if (ato > TCP_DELACK_MIN) {
3353 const struct tcp_sock *tp = tcp_sk(sk);
3354 int max_ato = HZ / 2;
3355
3356 if (icsk->icsk_ack.pingpong ||
3357 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED))
3358 max_ato = TCP_DELACK_MAX;
3359
3360 /* Slow path, intersegment interval is "high". */
3361
3362 /* If some rtt estimate is known, use it to bound delayed ack.
3363 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements
3364 * directly.
3365 */
3366 if (tp->srtt_us) {
3367 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3),
3368 TCP_DELACK_MIN);
3369
3370 if (rtt < max_ato)
3371 max_ato = rtt;
3372 }
3373
3374 ato = min(ato, max_ato);
3375 }
3376
3377 /* Stay within the limit we were given */
3378 timeout = jiffies + ato;
3379
3380 /* Use new timeout only if there wasn't a older one earlier. */
3381 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
3382 /* If delack timer was blocked or is about to expire,
3383 * send ACK now.
3384 */
3385 if (icsk->icsk_ack.blocked ||
3386 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
3387 tcp_send_ack(sk);
3388 return;
3389 }
3390
3391 if (!time_before(timeout, icsk->icsk_ack.timeout))
3392 timeout = icsk->icsk_ack.timeout;
3393 }
3394 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
3395 icsk->icsk_ack.timeout = timeout;
3396 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
3397 }
3398
3399 /* This routine sends an ack and also updates the window. */
__tcp_send_ack(struct sock * sk,u32 rcv_nxt)3400 void __tcp_send_ack(struct sock *sk, u32 rcv_nxt)
3401 {
3402 struct sk_buff *buff;
3403
3404 /* If we have been reset, we may not send again. */
3405 if (sk->sk_state == TCP_CLOSE)
3406 return;
3407
3408 /* We are not putting this on the write queue, so
3409 * tcp_transmit_skb() will set the ownership to this
3410 * sock.
3411 */
3412 buff = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3413 if (!buff) {
3414 inet_csk_schedule_ack(sk);
3415 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
3416 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
3417 TCP_DELACK_MAX, TCP_RTO_MAX);
3418 return;
3419 }
3420
3421 /* Reserve space for headers and prepare control bits. */
3422 skb_reserve(buff, MAX_TCP_HEADER);
3423 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK);
3424
3425 /* We do not want pure acks influencing TCP Small Queues or fq/pacing
3426 * too much.
3427 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784
3428 * We also avoid tcp_wfree() overhead (cache line miss accessing
3429 * tp->tsq_flags) by using regular sock_wfree()
3430 */
3431 skb_set_tcp_pure_ack(buff);
3432
3433 /* Send it off, this clears delayed acks for us. */
3434 skb_mstamp_get(&buff->skb_mstamp);
3435 __tcp_transmit_skb(sk, buff, 0, sk_gfp_atomic(sk, GFP_ATOMIC), rcv_nxt);
3436 }
3437 EXPORT_SYMBOL_GPL(__tcp_send_ack);
3438
tcp_send_ack(struct sock * sk)3439 void tcp_send_ack(struct sock *sk)
3440 {
3441 __tcp_send_ack(sk, tcp_sk(sk)->rcv_nxt);
3442 }
3443
3444 /* This routine sends a packet with an out of date sequence
3445 * number. It assumes the other end will try to ack it.
3446 *
3447 * Question: what should we make while urgent mode?
3448 * 4.4BSD forces sending single byte of data. We cannot send
3449 * out of window data, because we have SND.NXT==SND.MAX...
3450 *
3451 * Current solution: to send TWO zero-length segments in urgent mode:
3452 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is
3453 * out-of-date with SND.UNA-1 to probe window.
3454 */
tcp_xmit_probe_skb(struct sock * sk,int urgent,int mib)3455 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib)
3456 {
3457 struct tcp_sock *tp = tcp_sk(sk);
3458 struct sk_buff *skb;
3459
3460 /* We don't queue it, tcp_transmit_skb() sets ownership. */
3461 skb = alloc_skb(MAX_TCP_HEADER, sk_gfp_atomic(sk, GFP_ATOMIC));
3462 if (!skb)
3463 return -1;
3464
3465 /* Reserve space for headers and set control bits. */
3466 skb_reserve(skb, MAX_TCP_HEADER);
3467 /* Use a previous sequence. This should cause the other
3468 * end to send an ack. Don't queue or clone SKB, just
3469 * send it.
3470 */
3471 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK);
3472 skb_mstamp_get(&skb->skb_mstamp);
3473 NET_INC_STATS(sock_net(sk), mib);
3474 return tcp_transmit_skb(sk, skb, 0, GFP_ATOMIC);
3475 }
3476
tcp_send_window_probe(struct sock * sk)3477 void tcp_send_window_probe(struct sock *sk)
3478 {
3479 if (sk->sk_state == TCP_ESTABLISHED) {
3480 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1;
3481 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE);
3482 }
3483 }
3484
3485 /* Initiate keepalive or window probe from timer. */
tcp_write_wakeup(struct sock * sk,int mib)3486 int tcp_write_wakeup(struct sock *sk, int mib)
3487 {
3488 struct tcp_sock *tp = tcp_sk(sk);
3489 struct sk_buff *skb;
3490
3491 if (sk->sk_state == TCP_CLOSE)
3492 return -1;
3493
3494 skb = tcp_send_head(sk);
3495 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) {
3496 int err;
3497 unsigned int mss = tcp_current_mss(sk);
3498 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
3499
3500 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq))
3501 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq;
3502
3503 /* We are probing the opening of a window
3504 * but the window size is != 0
3505 * must have been a result SWS avoidance ( sender )
3506 */
3507 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq ||
3508 skb->len > mss) {
3509 seg_size = min(seg_size, mss);
3510 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3511 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC))
3512 return -1;
3513 } else if (!tcp_skb_pcount(skb))
3514 tcp_set_skb_tso_segs(skb, mss);
3515
3516 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH;
3517 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);
3518 if (!err)
3519 tcp_event_new_data_sent(sk, skb);
3520 return err;
3521 } else {
3522 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF))
3523 tcp_xmit_probe_skb(sk, 1, mib);
3524 return tcp_xmit_probe_skb(sk, 0, mib);
3525 }
3526 }
3527
3528 /* A window probe timeout has occurred. If window is not closed send
3529 * a partial packet else a zero probe.
3530 */
tcp_send_probe0(struct sock * sk)3531 void tcp_send_probe0(struct sock *sk)
3532 {
3533 struct inet_connection_sock *icsk = inet_csk(sk);
3534 struct tcp_sock *tp = tcp_sk(sk);
3535 unsigned long probe_max;
3536 int err;
3537
3538 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE);
3539
3540 if (tp->packets_out || !tcp_send_head(sk)) {
3541 /* Cancel probe timer, if it is not required. */
3542 icsk->icsk_probes_out = 0;
3543 icsk->icsk_backoff = 0;
3544 return;
3545 }
3546
3547 if (err <= 0) {
3548 if (icsk->icsk_backoff < sysctl_tcp_retries2)
3549 icsk->icsk_backoff++;
3550 icsk->icsk_probes_out++;
3551 probe_max = TCP_RTO_MAX;
3552 } else {
3553 /* If packet was not sent due to local congestion,
3554 * do not backoff and do not remember icsk_probes_out.
3555 * Let local senders to fight for local resources.
3556 *
3557 * Use accumulated backoff yet.
3558 */
3559 if (!icsk->icsk_probes_out)
3560 icsk->icsk_probes_out = 1;
3561 probe_max = TCP_RESOURCE_PROBE_INTERVAL;
3562 }
3563 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3564 tcp_probe0_when(sk, probe_max),
3565 TCP_RTO_MAX);
3566 }
3567
tcp_rtx_synack(const struct sock * sk,struct request_sock * req)3568 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req)
3569 {
3570 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific;
3571 struct flowi fl;
3572 int res;
3573
3574 tcp_rsk(req)->txhash = net_tx_rndhash();
3575 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, true);
3576 if (!res) {
3577 TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
3578 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNRETRANS);
3579 }
3580 return res;
3581 }
3582 EXPORT_SYMBOL(tcp_rtx_synack);
3583