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