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 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 66 int push_one, gfp_t gfp); 67 68 /* Account for new data that has been sent to the network. */ 69 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb) 70 { 71 struct inet_connection_sock *icsk = inet_csk(sk); 72 struct tcp_sock *tp = tcp_sk(sk); 73 unsigned int prior_packets = tp->packets_out; 74 75 tcp_advance_send_head(sk, skb); 76 tp->snd_nxt = TCP_SKB_CB(skb)->end_seq; 77 78 tp->packets_out += tcp_skb_pcount(skb); 79 if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS || 80 icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) { 81 tcp_rearm_rto(sk); 82 } 83 84 NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT, 85 tcp_skb_pcount(skb)); 86 } 87 88 /* SND.NXT, if window was not shrunk. 89 * If window has been shrunk, what should we make? It is not clear at all. 90 * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( 91 * Anything in between SND.UNA...SND.UNA+SND.WND also can be already 92 * invalid. OK, let's make this for now: 93 */ 94 static inline __u32 tcp_acceptable_seq(const struct sock *sk) 95 { 96 const struct tcp_sock *tp = tcp_sk(sk); 97 98 if (!before(tcp_wnd_end(tp), tp->snd_nxt)) 99 return tp->snd_nxt; 100 else 101 return tcp_wnd_end(tp); 102 } 103 104 /* Calculate mss to advertise in SYN segment. 105 * RFC1122, RFC1063, draft-ietf-tcpimpl-pmtud-01 state that: 106 * 107 * 1. It is independent of path mtu. 108 * 2. Ideally, it is maximal possible segment size i.e. 65535-40. 109 * 3. For IPv4 it is reasonable to calculate it from maximal MTU of 110 * attached devices, because some buggy hosts are confused by 111 * large MSS. 112 * 4. We do not make 3, we advertise MSS, calculated from first 113 * hop device mtu, but allow to raise it to ip_rt_min_advmss. 114 * This may be overridden via information stored in routing table. 115 * 5. Value 65535 for MSS is valid in IPv6 and means "as large as possible, 116 * probably even Jumbo". 117 */ 118 static __u16 tcp_advertise_mss(struct sock *sk) 119 { 120 struct tcp_sock *tp = tcp_sk(sk); 121 const struct dst_entry *dst = __sk_dst_get(sk); 122 int mss = tp->advmss; 123 124 if (dst) { 125 unsigned int metric = dst_metric_advmss(dst); 126 127 if (metric < mss) { 128 mss = metric; 129 tp->advmss = mss; 130 } 131 } 132 133 return (__u16)mss; 134 } 135 136 /* RFC2861. Reset CWND after idle period longer RTO to "restart window". 137 * This is the first part of cwnd validation mechanism. 138 */ 139 void tcp_cwnd_restart(struct sock *sk, s32 delta) 140 { 141 struct tcp_sock *tp = tcp_sk(sk); 142 u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk)); 143 u32 cwnd = tp->snd_cwnd; 144 145 tcp_ca_event(sk, CA_EVENT_CWND_RESTART); 146 147 tp->snd_ssthresh = tcp_current_ssthresh(sk); 148 restart_cwnd = min(restart_cwnd, cwnd); 149 150 while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd) 151 cwnd >>= 1; 152 tp->snd_cwnd = max(cwnd, restart_cwnd); 153 tp->snd_cwnd_stamp = tcp_time_stamp; 154 tp->snd_cwnd_used = 0; 155 } 156 157 /* Congestion state accounting after a packet has been sent. */ 158 static void tcp_event_data_sent(struct tcp_sock *tp, 159 struct sock *sk) 160 { 161 struct inet_connection_sock *icsk = inet_csk(sk); 162 const u32 now = tcp_time_stamp; 163 164 if (tcp_packets_in_flight(tp) == 0) 165 tcp_ca_event(sk, CA_EVENT_TX_START); 166 167 tp->lsndtime = now; 168 169 /* If it is a reply for ato after last received 170 * packet, enter pingpong mode. 171 */ 172 if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) 173 icsk->icsk_ack.pingpong = 1; 174 } 175 176 /* Account for an ACK we sent. */ 177 static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts) 178 { 179 tcp_dec_quickack_mode(sk, pkts); 180 inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK); 181 } 182 183 184 u32 tcp_default_init_rwnd(u32 mss) 185 { 186 /* Initial receive window should be twice of TCP_INIT_CWND to 187 * enable proper sending of new unsent data during fast recovery 188 * (RFC 3517, Section 4, NextSeg() rule (2)). Further place a 189 * limit when mss is larger than 1460. 190 */ 191 u32 init_rwnd = TCP_INIT_CWND * 2; 192 193 if (mss > 1460) 194 init_rwnd = max((1460 * init_rwnd) / mss, 2U); 195 return init_rwnd; 196 } 197 198 /* Determine a window scaling and initial window to offer. 199 * Based on the assumption that the given amount of space 200 * will be offered. Store the results in the tp structure. 201 * NOTE: for smooth operation initial space offering should 202 * be a multiple of mss if possible. We assume here that mss >= 1. 203 * This MUST be enforced by all callers. 204 */ 205 void tcp_select_initial_window(int __space, __u32 mss, 206 __u32 *rcv_wnd, __u32 *window_clamp, 207 int wscale_ok, __u8 *rcv_wscale, 208 __u32 init_rcv_wnd) 209 { 210 unsigned int space = (__space < 0 ? 0 : __space); 211 212 /* If no clamp set the clamp to the max possible scaled window */ 213 if (*window_clamp == 0) 214 (*window_clamp) = (65535 << 14); 215 space = min(*window_clamp, space); 216 217 /* Quantize space offering to a multiple of mss if possible. */ 218 if (space > mss) 219 space = (space / mss) * mss; 220 221 /* NOTE: offering an initial window larger than 32767 222 * will break some buggy TCP stacks. If the admin tells us 223 * it is likely we could be speaking with such a buggy stack 224 * we will truncate our initial window offering to 32K-1 225 * unless the remote has sent us a window scaling option, 226 * which we interpret as a sign the remote TCP is not 227 * misinterpreting the window field as a signed quantity. 228 */ 229 if (sysctl_tcp_workaround_signed_windows) 230 (*rcv_wnd) = min(space, MAX_TCP_WINDOW); 231 else 232 (*rcv_wnd) = space; 233 234 (*rcv_wscale) = 0; 235 if (wscale_ok) { 236 /* Set window scaling on max possible window 237 * See RFC1323 for an explanation of the limit to 14 238 */ 239 space = max_t(u32, space, sysctl_tcp_rmem[2]); 240 space = max_t(u32, space, sysctl_rmem_max); 241 space = min_t(u32, space, *window_clamp); 242 while (space > 65535 && (*rcv_wscale) < 14) { 243 space >>= 1; 244 (*rcv_wscale)++; 245 } 246 } 247 248 if (mss > (1 << *rcv_wscale)) { 249 if (!init_rcv_wnd) /* Use default unless specified otherwise */ 250 init_rcv_wnd = tcp_default_init_rwnd(mss); 251 *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss); 252 } 253 254 /* Set the clamp no higher than max representable value */ 255 (*window_clamp) = min(65535U << (*rcv_wscale), *window_clamp); 256 } 257 EXPORT_SYMBOL(tcp_select_initial_window); 258 259 /* Chose a new window to advertise, update state in tcp_sock for the 260 * socket, and return result with RFC1323 scaling applied. The return 261 * value can be stuffed directly into th->window for an outgoing 262 * frame. 263 */ 264 static u16 tcp_select_window(struct sock *sk) 265 { 266 struct tcp_sock *tp = tcp_sk(sk); 267 u32 old_win = tp->rcv_wnd; 268 u32 cur_win = tcp_receive_window(tp); 269 u32 new_win = __tcp_select_window(sk); 270 271 /* Never shrink the offered window */ 272 if (new_win < cur_win) { 273 /* Danger Will Robinson! 274 * Don't update rcv_wup/rcv_wnd here or else 275 * we will not be able to advertise a zero 276 * window in time. --DaveM 277 * 278 * Relax Will Robinson. 279 */ 280 if (new_win == 0) 281 NET_INC_STATS(sock_net(sk), 282 LINUX_MIB_TCPWANTZEROWINDOWADV); 283 new_win = ALIGN(cur_win, 1 << tp->rx_opt.rcv_wscale); 284 } 285 tp->rcv_wnd = new_win; 286 tp->rcv_wup = tp->rcv_nxt; 287 288 /* Make sure we do not exceed the maximum possible 289 * scaled window. 290 */ 291 if (!tp->rx_opt.rcv_wscale && sysctl_tcp_workaround_signed_windows) 292 new_win = min(new_win, MAX_TCP_WINDOW); 293 else 294 new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale)); 295 296 /* RFC1323 scaling applied */ 297 new_win >>= tp->rx_opt.rcv_wscale; 298 299 /* If we advertise zero window, disable fast path. */ 300 if (new_win == 0) { 301 tp->pred_flags = 0; 302 if (old_win) 303 NET_INC_STATS(sock_net(sk), 304 LINUX_MIB_TCPTOZEROWINDOWADV); 305 } else if (old_win == 0) { 306 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFROMZEROWINDOWADV); 307 } 308 309 return new_win; 310 } 311 312 /* Packet ECN state for a SYN-ACK */ 313 static void tcp_ecn_send_synack(struct sock *sk, struct sk_buff *skb) 314 { 315 const struct tcp_sock *tp = tcp_sk(sk); 316 317 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_CWR; 318 if (!(tp->ecn_flags & TCP_ECN_OK)) 319 TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_ECE; 320 else if (tcp_ca_needs_ecn(sk)) 321 INET_ECN_xmit(sk); 322 } 323 324 /* Packet ECN state for a SYN. */ 325 static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb) 326 { 327 struct tcp_sock *tp = tcp_sk(sk); 328 bool use_ecn = sock_net(sk)->ipv4.sysctl_tcp_ecn == 1 || 329 tcp_ca_needs_ecn(sk); 330 331 if (!use_ecn) { 332 const struct dst_entry *dst = __sk_dst_get(sk); 333 334 if (dst && dst_feature(dst, RTAX_FEATURE_ECN)) 335 use_ecn = true; 336 } 337 338 tp->ecn_flags = 0; 339 340 if (use_ecn) { 341 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ECE | TCPHDR_CWR; 342 tp->ecn_flags = TCP_ECN_OK; 343 if (tcp_ca_needs_ecn(sk)) 344 INET_ECN_xmit(sk); 345 } 346 } 347 348 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb) 349 { 350 if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback) 351 /* tp->ecn_flags are cleared at a later point in time when 352 * SYN ACK is ultimatively being received. 353 */ 354 TCP_SKB_CB(skb)->tcp_flags &= ~(TCPHDR_ECE | TCPHDR_CWR); 355 } 356 357 static void 358 tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th) 359 { 360 if (inet_rsk(req)->ecn_ok) 361 th->ece = 1; 362 } 363 364 /* Set up ECN state for a packet on a ESTABLISHED socket that is about to 365 * be sent. 366 */ 367 static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb, 368 struct tcphdr *th, int tcp_header_len) 369 { 370 struct tcp_sock *tp = tcp_sk(sk); 371 372 if (tp->ecn_flags & TCP_ECN_OK) { 373 /* Not-retransmitted data segment: set ECT and inject CWR. */ 374 if (skb->len != tcp_header_len && 375 !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) { 376 INET_ECN_xmit(sk); 377 if (tp->ecn_flags & TCP_ECN_QUEUE_CWR) { 378 tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; 379 th->cwr = 1; 380 skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ECN; 381 } 382 } else if (!tcp_ca_needs_ecn(sk)) { 383 /* ACK or retransmitted segment: clear ECT|CE */ 384 INET_ECN_dontxmit(sk); 385 } 386 if (tp->ecn_flags & TCP_ECN_DEMAND_CWR) 387 th->ece = 1; 388 } 389 } 390 391 /* Constructs common control bits of non-data skb. If SYN/FIN is present, 392 * auto increment end seqno. 393 */ 394 static void tcp_init_nondata_skb(struct sk_buff *skb, u32 seq, u8 flags) 395 { 396 skb->ip_summed = CHECKSUM_PARTIAL; 397 skb->csum = 0; 398 399 TCP_SKB_CB(skb)->tcp_flags = flags; 400 TCP_SKB_CB(skb)->sacked = 0; 401 402 tcp_skb_pcount_set(skb, 1); 403 404 TCP_SKB_CB(skb)->seq = seq; 405 if (flags & (TCPHDR_SYN | TCPHDR_FIN)) 406 seq++; 407 TCP_SKB_CB(skb)->end_seq = seq; 408 } 409 410 static inline bool tcp_urg_mode(const struct tcp_sock *tp) 411 { 412 return tp->snd_una != tp->snd_up; 413 } 414 415 #define OPTION_SACK_ADVERTISE (1 << 0) 416 #define OPTION_TS (1 << 1) 417 #define OPTION_MD5 (1 << 2) 418 #define OPTION_WSCALE (1 << 3) 419 #define OPTION_FAST_OPEN_COOKIE (1 << 8) 420 421 struct tcp_out_options { 422 u16 options; /* bit field of OPTION_* */ 423 u16 mss; /* 0 to disable */ 424 u8 ws; /* window scale, 0 to disable */ 425 u8 num_sack_blocks; /* number of SACK blocks to include */ 426 u8 hash_size; /* bytes in hash_location */ 427 __u8 *hash_location; /* temporary pointer, overloaded */ 428 __u32 tsval, tsecr; /* need to include OPTION_TS */ 429 struct tcp_fastopen_cookie *fastopen_cookie; /* Fast open cookie */ 430 }; 431 432 /* Write previously computed TCP options to the packet. 433 * 434 * Beware: Something in the Internet is very sensitive to the ordering of 435 * TCP options, we learned this through the hard way, so be careful here. 436 * Luckily we can at least blame others for their non-compliance but from 437 * inter-operability perspective it seems that we're somewhat stuck with 438 * the ordering which we have been using if we want to keep working with 439 * those broken things (not that it currently hurts anybody as there isn't 440 * particular reason why the ordering would need to be changed). 441 * 442 * At least SACK_PERM as the first option is known to lead to a disaster 443 * (but it may well be that other scenarios fail similarly). 444 */ 445 static void tcp_options_write(__be32 *ptr, struct tcp_sock *tp, 446 struct tcp_out_options *opts) 447 { 448 u16 options = opts->options; /* mungable copy */ 449 450 if (unlikely(OPTION_MD5 & options)) { 451 *ptr++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | 452 (TCPOPT_MD5SIG << 8) | TCPOLEN_MD5SIG); 453 /* overload cookie hash location */ 454 opts->hash_location = (__u8 *)ptr; 455 ptr += 4; 456 } 457 458 if (unlikely(opts->mss)) { 459 *ptr++ = htonl((TCPOPT_MSS << 24) | 460 (TCPOLEN_MSS << 16) | 461 opts->mss); 462 } 463 464 if (likely(OPTION_TS & options)) { 465 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 466 *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | 467 (TCPOLEN_SACK_PERM << 16) | 468 (TCPOPT_TIMESTAMP << 8) | 469 TCPOLEN_TIMESTAMP); 470 options &= ~OPTION_SACK_ADVERTISE; 471 } else { 472 *ptr++ = htonl((TCPOPT_NOP << 24) | 473 (TCPOPT_NOP << 16) | 474 (TCPOPT_TIMESTAMP << 8) | 475 TCPOLEN_TIMESTAMP); 476 } 477 *ptr++ = htonl(opts->tsval); 478 *ptr++ = htonl(opts->tsecr); 479 } 480 481 if (unlikely(OPTION_SACK_ADVERTISE & options)) { 482 *ptr++ = htonl((TCPOPT_NOP << 24) | 483 (TCPOPT_NOP << 16) | 484 (TCPOPT_SACK_PERM << 8) | 485 TCPOLEN_SACK_PERM); 486 } 487 488 if (unlikely(OPTION_WSCALE & options)) { 489 *ptr++ = htonl((TCPOPT_NOP << 24) | 490 (TCPOPT_WINDOW << 16) | 491 (TCPOLEN_WINDOW << 8) | 492 opts->ws); 493 } 494 495 if (unlikely(opts->num_sack_blocks)) { 496 struct tcp_sack_block *sp = tp->rx_opt.dsack ? 497 tp->duplicate_sack : tp->selective_acks; 498 int this_sack; 499 500 *ptr++ = htonl((TCPOPT_NOP << 24) | 501 (TCPOPT_NOP << 16) | 502 (TCPOPT_SACK << 8) | 503 (TCPOLEN_SACK_BASE + (opts->num_sack_blocks * 504 TCPOLEN_SACK_PERBLOCK))); 505 506 for (this_sack = 0; this_sack < opts->num_sack_blocks; 507 ++this_sack) { 508 *ptr++ = htonl(sp[this_sack].start_seq); 509 *ptr++ = htonl(sp[this_sack].end_seq); 510 } 511 512 tp->rx_opt.dsack = 0; 513 } 514 515 if (unlikely(OPTION_FAST_OPEN_COOKIE & options)) { 516 struct tcp_fastopen_cookie *foc = opts->fastopen_cookie; 517 u8 *p = (u8 *)ptr; 518 u32 len; /* Fast Open option length */ 519 520 if (foc->exp) { 521 len = TCPOLEN_EXP_FASTOPEN_BASE + foc->len; 522 *ptr = htonl((TCPOPT_EXP << 24) | (len << 16) | 523 TCPOPT_FASTOPEN_MAGIC); 524 p += TCPOLEN_EXP_FASTOPEN_BASE; 525 } else { 526 len = TCPOLEN_FASTOPEN_BASE + foc->len; 527 *p++ = TCPOPT_FASTOPEN; 528 *p++ = len; 529 } 530 531 memcpy(p, foc->val, foc->len); 532 if ((len & 3) == 2) { 533 p[foc->len] = TCPOPT_NOP; 534 p[foc->len + 1] = TCPOPT_NOP; 535 } 536 ptr += (len + 3) >> 2; 537 } 538 } 539 540 /* Compute TCP options for SYN packets. This is not the final 541 * network wire format yet. 542 */ 543 static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb, 544 struct tcp_out_options *opts, 545 struct tcp_md5sig_key **md5) 546 { 547 struct tcp_sock *tp = tcp_sk(sk); 548 unsigned int remaining = MAX_TCP_OPTION_SPACE; 549 struct tcp_fastopen_request *fastopen = tp->fastopen_req; 550 551 #ifdef CONFIG_TCP_MD5SIG 552 *md5 = tp->af_specific->md5_lookup(sk, sk); 553 if (*md5) { 554 opts->options |= OPTION_MD5; 555 remaining -= TCPOLEN_MD5SIG_ALIGNED; 556 } 557 #else 558 *md5 = NULL; 559 #endif 560 561 /* We always get an MSS option. The option bytes which will be seen in 562 * normal data packets should timestamps be used, must be in the MSS 563 * advertised. But we subtract them from tp->mss_cache so that 564 * calculations in tcp_sendmsg are simpler etc. So account for this 565 * fact here if necessary. If we don't do this correctly, as a 566 * receiver we won't recognize data packets as being full sized when we 567 * should, and thus we won't abide by the delayed ACK rules correctly. 568 * SACKs don't matter, we never delay an ACK when we have any of those 569 * going out. */ 570 opts->mss = tcp_advertise_mss(sk); 571 remaining -= TCPOLEN_MSS_ALIGNED; 572 573 if (likely(sysctl_tcp_timestamps && !*md5)) { 574 opts->options |= OPTION_TS; 575 opts->tsval = tcp_skb_timestamp(skb) + tp->tsoffset; 576 opts->tsecr = tp->rx_opt.ts_recent; 577 remaining -= TCPOLEN_TSTAMP_ALIGNED; 578 } 579 if (likely(sysctl_tcp_window_scaling)) { 580 opts->ws = tp->rx_opt.rcv_wscale; 581 opts->options |= OPTION_WSCALE; 582 remaining -= TCPOLEN_WSCALE_ALIGNED; 583 } 584 if (likely(sysctl_tcp_sack)) { 585 opts->options |= OPTION_SACK_ADVERTISE; 586 if (unlikely(!(OPTION_TS & opts->options))) 587 remaining -= TCPOLEN_SACKPERM_ALIGNED; 588 } 589 590 if (fastopen && fastopen->cookie.len >= 0) { 591 u32 need = fastopen->cookie.len; 592 593 need += fastopen->cookie.exp ? TCPOLEN_EXP_FASTOPEN_BASE : 594 TCPOLEN_FASTOPEN_BASE; 595 need = (need + 3) & ~3U; /* Align to 32 bits */ 596 if (remaining >= need) { 597 opts->options |= OPTION_FAST_OPEN_COOKIE; 598 opts->fastopen_cookie = &fastopen->cookie; 599 remaining -= need; 600 tp->syn_fastopen = 1; 601 tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0; 602 } 603 } 604 605 return MAX_TCP_OPTION_SPACE - remaining; 606 } 607 608 /* Set up TCP options for SYN-ACKs. */ 609 static unsigned int tcp_synack_options(struct request_sock *req, 610 unsigned int mss, struct sk_buff *skb, 611 struct tcp_out_options *opts, 612 const struct tcp_md5sig_key *md5, 613 struct tcp_fastopen_cookie *foc) 614 { 615 struct inet_request_sock *ireq = inet_rsk(req); 616 unsigned int remaining = MAX_TCP_OPTION_SPACE; 617 618 #ifdef CONFIG_TCP_MD5SIG 619 if (md5) { 620 opts->options |= OPTION_MD5; 621 remaining -= TCPOLEN_MD5SIG_ALIGNED; 622 623 /* We can't fit any SACK blocks in a packet with MD5 + TS 624 * options. There was discussion about disabling SACK 625 * rather than TS in order to fit in better with old, 626 * buggy kernels, but that was deemed to be unnecessary. 627 */ 628 ireq->tstamp_ok &= !ireq->sack_ok; 629 } 630 #endif 631 632 /* We always send an MSS option. */ 633 opts->mss = mss; 634 remaining -= TCPOLEN_MSS_ALIGNED; 635 636 if (likely(ireq->wscale_ok)) { 637 opts->ws = ireq->rcv_wscale; 638 opts->options |= OPTION_WSCALE; 639 remaining -= TCPOLEN_WSCALE_ALIGNED; 640 } 641 if (likely(ireq->tstamp_ok)) { 642 opts->options |= OPTION_TS; 643 opts->tsval = tcp_skb_timestamp(skb) + tcp_rsk(req)->ts_off; 644 opts->tsecr = req->ts_recent; 645 remaining -= TCPOLEN_TSTAMP_ALIGNED; 646 } 647 if (likely(ireq->sack_ok)) { 648 opts->options |= OPTION_SACK_ADVERTISE; 649 if (unlikely(!ireq->tstamp_ok)) 650 remaining -= TCPOLEN_SACKPERM_ALIGNED; 651 } 652 if (foc != NULL && foc->len >= 0) { 653 u32 need = foc->len; 654 655 need += foc->exp ? TCPOLEN_EXP_FASTOPEN_BASE : 656 TCPOLEN_FASTOPEN_BASE; 657 need = (need + 3) & ~3U; /* Align to 32 bits */ 658 if (remaining >= need) { 659 opts->options |= OPTION_FAST_OPEN_COOKIE; 660 opts->fastopen_cookie = foc; 661 remaining -= need; 662 } 663 } 664 665 return MAX_TCP_OPTION_SPACE - remaining; 666 } 667 668 /* Compute TCP options for ESTABLISHED sockets. This is not the 669 * final wire format yet. 670 */ 671 static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb, 672 struct tcp_out_options *opts, 673 struct tcp_md5sig_key **md5) 674 { 675 struct tcp_sock *tp = tcp_sk(sk); 676 unsigned int size = 0; 677 unsigned int eff_sacks; 678 679 opts->options = 0; 680 681 #ifdef CONFIG_TCP_MD5SIG 682 *md5 = tp->af_specific->md5_lookup(sk, sk); 683 if (unlikely(*md5)) { 684 opts->options |= OPTION_MD5; 685 size += TCPOLEN_MD5SIG_ALIGNED; 686 } 687 #else 688 *md5 = NULL; 689 #endif 690 691 if (likely(tp->rx_opt.tstamp_ok)) { 692 opts->options |= OPTION_TS; 693 opts->tsval = skb ? tcp_skb_timestamp(skb) + tp->tsoffset : 0; 694 opts->tsecr = tp->rx_opt.ts_recent; 695 size += TCPOLEN_TSTAMP_ALIGNED; 696 } 697 698 eff_sacks = tp->rx_opt.num_sacks + tp->rx_opt.dsack; 699 if (unlikely(eff_sacks)) { 700 const unsigned int remaining = MAX_TCP_OPTION_SPACE - size; 701 opts->num_sack_blocks = 702 min_t(unsigned int, eff_sacks, 703 (remaining - TCPOLEN_SACK_BASE_ALIGNED) / 704 TCPOLEN_SACK_PERBLOCK); 705 size += TCPOLEN_SACK_BASE_ALIGNED + 706 opts->num_sack_blocks * TCPOLEN_SACK_PERBLOCK; 707 } 708 709 return size; 710 } 711 712 713 /* TCP SMALL QUEUES (TSQ) 714 * 715 * TSQ goal is to keep small amount of skbs per tcp flow in tx queues (qdisc+dev) 716 * to reduce RTT and bufferbloat. 717 * We do this using a special skb destructor (tcp_wfree). 718 * 719 * Its important tcp_wfree() can be replaced by sock_wfree() in the event skb 720 * needs to be reallocated in a driver. 721 * The invariant being skb->truesize subtracted from sk->sk_wmem_alloc 722 * 723 * Since transmit from skb destructor is forbidden, we use a tasklet 724 * to process all sockets that eventually need to send more skbs. 725 * We use one tasklet per cpu, with its own queue of sockets. 726 */ 727 struct tsq_tasklet { 728 struct tasklet_struct tasklet; 729 struct list_head head; /* queue of tcp sockets */ 730 }; 731 static DEFINE_PER_CPU(struct tsq_tasklet, tsq_tasklet); 732 733 static void tcp_tsq_handler(struct sock *sk) 734 { 735 if ((1 << sk->sk_state) & 736 (TCPF_ESTABLISHED | TCPF_FIN_WAIT1 | TCPF_CLOSING | 737 TCPF_CLOSE_WAIT | TCPF_LAST_ACK)) { 738 struct tcp_sock *tp = tcp_sk(sk); 739 740 if (tp->lost_out > tp->retrans_out && 741 tp->snd_cwnd > tcp_packets_in_flight(tp)) 742 tcp_xmit_retransmit_queue(sk); 743 744 tcp_write_xmit(sk, tcp_current_mss(sk), tp->nonagle, 745 0, GFP_ATOMIC); 746 } 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 smp_mb__before_atomic(); 773 clear_bit(TSQ_QUEUED, &sk->sk_tsq_flags); 774 775 if (!sk->sk_lock.owned && 776 test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) { 777 bh_lock_sock(sk); 778 if (!sock_owned_by_user(sk)) { 779 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags); 780 tcp_tsq_handler(sk); 781 } 782 bh_unlock_sock(sk); 783 } 784 785 sk_free(sk); 786 } 787 } 788 789 #define TCP_DEFERRED_ALL (TCPF_TSQ_DEFERRED | \ 790 TCPF_WRITE_TIMER_DEFERRED | \ 791 TCPF_DELACK_TIMER_DEFERRED | \ 792 TCPF_MTU_REDUCED_DEFERRED) 793 /** 794 * tcp_release_cb - tcp release_sock() callback 795 * @sk: socket 796 * 797 * called from release_sock() to perform protocol dependent 798 * actions before socket release. 799 */ 800 void tcp_release_cb(struct sock *sk) 801 { 802 unsigned long flags, nflags; 803 804 /* perform an atomic operation only if at least one flag is set */ 805 do { 806 flags = sk->sk_tsq_flags; 807 if (!(flags & TCP_DEFERRED_ALL)) 808 return; 809 nflags = flags & ~TCP_DEFERRED_ALL; 810 } while (cmpxchg(&sk->sk_tsq_flags, flags, nflags) != flags); 811 812 if (flags & TCPF_TSQ_DEFERRED) 813 tcp_tsq_handler(sk); 814 815 /* Here begins the tricky part : 816 * We are called from release_sock() with : 817 * 1) BH disabled 818 * 2) sk_lock.slock spinlock held 819 * 3) socket owned by us (sk->sk_lock.owned == 1) 820 * 821 * But following code is meant to be called from BH handlers, 822 * so we should keep BH disabled, but early release socket ownership 823 */ 824 sock_release_ownership(sk); 825 826 if (flags & TCPF_WRITE_TIMER_DEFERRED) { 827 tcp_write_timer_handler(sk); 828 __sock_put(sk); 829 } 830 if (flags & TCPF_DELACK_TIMER_DEFERRED) { 831 tcp_delack_timer_handler(sk); 832 __sock_put(sk); 833 } 834 if (flags & TCPF_MTU_REDUCED_DEFERRED) { 835 inet_csk(sk)->icsk_af_ops->mtu_reduced(sk); 836 __sock_put(sk); 837 } 838 } 839 EXPORT_SYMBOL(tcp_release_cb); 840 841 void __init tcp_tasklet_init(void) 842 { 843 int i; 844 845 for_each_possible_cpu(i) { 846 struct tsq_tasklet *tsq = &per_cpu(tsq_tasklet, i); 847 848 INIT_LIST_HEAD(&tsq->head); 849 tasklet_init(&tsq->tasklet, 850 tcp_tasklet_func, 851 (unsigned long)tsq); 852 } 853 } 854 855 /* 856 * Write buffer destructor automatically called from kfree_skb. 857 * We can't xmit new skbs from this context, as we might already 858 * hold qdisc lock. 859 */ 860 void tcp_wfree(struct sk_buff *skb) 861 { 862 struct sock *sk = skb->sk; 863 struct tcp_sock *tp = tcp_sk(sk); 864 unsigned long flags, nval, oval; 865 int wmem; 866 867 /* Keep one reference on sk_wmem_alloc. 868 * Will be released by sk_free() from here or tcp_tasklet_func() 869 */ 870 wmem = atomic_sub_return(skb->truesize - 1, &sk->sk_wmem_alloc); 871 872 /* If this softirq is serviced by ksoftirqd, we are likely under stress. 873 * Wait until our queues (qdisc + devices) are drained. 874 * This gives : 875 * - less callbacks to tcp_write_xmit(), reducing stress (batches) 876 * - chance for incoming ACK (processed by another cpu maybe) 877 * to migrate this flow (skb->ooo_okay will be eventually set) 878 */ 879 if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current) 880 goto out; 881 882 for (oval = READ_ONCE(sk->sk_tsq_flags);; oval = nval) { 883 struct tsq_tasklet *tsq; 884 bool empty; 885 886 if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED)) 887 goto out; 888 889 nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED | TCPF_TSQ_DEFERRED; 890 nval = cmpxchg(&sk->sk_tsq_flags, oval, nval); 891 if (nval != oval) 892 continue; 893 894 /* queue this socket to tasklet queue */ 895 local_irq_save(flags); 896 tsq = this_cpu_ptr(&tsq_tasklet); 897 empty = list_empty(&tsq->head); 898 list_add(&tp->tsq_node, &tsq->head); 899 if (empty) 900 tasklet_schedule(&tsq->tasklet); 901 local_irq_restore(flags); 902 return; 903 } 904 out: 905 sk_free(sk); 906 } 907 908 /* This routine actually transmits TCP packets queued in by 909 * tcp_do_sendmsg(). This is used by both the initial 910 * transmission and possible later retransmissions. 911 * All SKB's seen here are completely headerless. It is our 912 * job to build the TCP header, and pass the packet down to 913 * IP so it can do the same plus pass the packet off to the 914 * device. 915 * 916 * We are working here with either a clone of the original 917 * SKB, or a fresh unique copy made by the retransmit engine. 918 */ 919 static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, 920 gfp_t gfp_mask) 921 { 922 const struct inet_connection_sock *icsk = inet_csk(sk); 923 struct inet_sock *inet; 924 struct tcp_sock *tp; 925 struct tcp_skb_cb *tcb; 926 struct tcp_out_options opts; 927 unsigned int tcp_options_size, tcp_header_size; 928 struct tcp_md5sig_key *md5; 929 struct tcphdr *th; 930 int err; 931 932 BUG_ON(!skb || !tcp_skb_pcount(skb)); 933 tp = tcp_sk(sk); 934 935 if (clone_it) { 936 skb_mstamp_get(&skb->skb_mstamp); 937 TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq 938 - tp->snd_una; 939 tcp_rate_skb_sent(sk, skb); 940 941 if (unlikely(skb_cloned(skb))) 942 skb = pskb_copy(skb, gfp_mask); 943 else 944 skb = skb_clone(skb, gfp_mask); 945 if (unlikely(!skb)) 946 return -ENOBUFS; 947 } 948 949 inet = inet_sk(sk); 950 tcb = TCP_SKB_CB(skb); 951 memset(&opts, 0, sizeof(opts)); 952 953 if (unlikely(tcb->tcp_flags & TCPHDR_SYN)) 954 tcp_options_size = tcp_syn_options(sk, skb, &opts, &md5); 955 else 956 tcp_options_size = tcp_established_options(sk, skb, &opts, 957 &md5); 958 tcp_header_size = tcp_options_size + sizeof(struct tcphdr); 959 960 /* if no packet is in qdisc/device queue, then allow XPS to select 961 * another queue. We can be called from tcp_tsq_handler() 962 * which holds one reference to sk_wmem_alloc. 963 * 964 * TODO: Ideally, in-flight pure ACK packets should not matter here. 965 * One way to get this would be to set skb->truesize = 2 on them. 966 */ 967 skb->ooo_okay = sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1); 968 969 skb_push(skb, tcp_header_size); 970 skb_reset_transport_header(skb); 971 972 skb_orphan(skb); 973 skb->sk = sk; 974 skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree; 975 skb_set_hash_from_sk(skb, sk); 976 atomic_add(skb->truesize, &sk->sk_wmem_alloc); 977 978 /* Build TCP header and checksum it. */ 979 th = (struct tcphdr *)skb->data; 980 th->source = inet->inet_sport; 981 th->dest = inet->inet_dport; 982 th->seq = htonl(tcb->seq); 983 th->ack_seq = htonl(tp->rcv_nxt); 984 *(((__be16 *)th) + 6) = htons(((tcp_header_size >> 2) << 12) | 985 tcb->tcp_flags); 986 987 th->check = 0; 988 th->urg_ptr = 0; 989 990 /* The urg_mode check is necessary during a below snd_una win probe */ 991 if (unlikely(tcp_urg_mode(tp) && before(tcb->seq, tp->snd_up))) { 992 if (before(tp->snd_up, tcb->seq + 0x10000)) { 993 th->urg_ptr = htons(tp->snd_up - tcb->seq); 994 th->urg = 1; 995 } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) { 996 th->urg_ptr = htons(0xFFFF); 997 th->urg = 1; 998 } 999 } 1000 1001 tcp_options_write((__be32 *)(th + 1), tp, &opts); 1002 skb_shinfo(skb)->gso_type = sk->sk_gso_type; 1003 if (likely(!(tcb->tcp_flags & TCPHDR_SYN))) { 1004 th->window = htons(tcp_select_window(sk)); 1005 tcp_ecn_send(sk, skb, th, tcp_header_size); 1006 } else { 1007 /* RFC1323: The window in SYN & SYN/ACK segments 1008 * is never scaled. 1009 */ 1010 th->window = htons(min(tp->rcv_wnd, 65535U)); 1011 } 1012 #ifdef CONFIG_TCP_MD5SIG 1013 /* Calculate the MD5 hash, as we have all we need now */ 1014 if (md5) { 1015 sk_nocaps_add(sk, NETIF_F_GSO_MASK); 1016 tp->af_specific->calc_md5_hash(opts.hash_location, 1017 md5, sk, skb); 1018 } 1019 #endif 1020 1021 icsk->icsk_af_ops->send_check(sk, skb); 1022 1023 if (likely(tcb->tcp_flags & TCPHDR_ACK)) 1024 tcp_event_ack_sent(sk, tcp_skb_pcount(skb)); 1025 1026 if (skb->len != tcp_header_size) { 1027 tcp_event_data_sent(tp, sk); 1028 tp->data_segs_out += tcp_skb_pcount(skb); 1029 } 1030 1031 if (after(tcb->end_seq, tp->snd_nxt) || tcb->seq == tcb->end_seq) 1032 TCP_ADD_STATS(sock_net(sk), TCP_MIB_OUTSEGS, 1033 tcp_skb_pcount(skb)); 1034 1035 tp->segs_out += tcp_skb_pcount(skb); 1036 /* OK, its time to fill skb_shinfo(skb)->gso_{segs|size} */ 1037 skb_shinfo(skb)->gso_segs = tcp_skb_pcount(skb); 1038 skb_shinfo(skb)->gso_size = tcp_skb_mss(skb); 1039 1040 /* Our usage of tstamp should remain private */ 1041 skb->tstamp = 0; 1042 1043 /* Cleanup our debris for IP stacks */ 1044 memset(skb->cb, 0, max(sizeof(struct inet_skb_parm), 1045 sizeof(struct inet6_skb_parm))); 1046 1047 err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl); 1048 1049 if (likely(err <= 0)) 1050 return err; 1051 1052 tcp_enter_cwr(sk); 1053 1054 return net_xmit_eval(err); 1055 } 1056 1057 /* This routine just queues the buffer for sending. 1058 * 1059 * NOTE: probe0 timer is not checked, do not forget tcp_push_pending_frames, 1060 * otherwise socket can stall. 1061 */ 1062 static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb) 1063 { 1064 struct tcp_sock *tp = tcp_sk(sk); 1065 1066 /* Advance write_seq and place onto the write_queue. */ 1067 tp->write_seq = TCP_SKB_CB(skb)->end_seq; 1068 __skb_header_release(skb); 1069 tcp_add_write_queue_tail(sk, skb); 1070 sk->sk_wmem_queued += skb->truesize; 1071 sk_mem_charge(sk, skb->truesize); 1072 } 1073 1074 /* Initialize TSO segments for a packet. */ 1075 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now) 1076 { 1077 if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) { 1078 /* Avoid the costly divide in the normal 1079 * non-TSO case. 1080 */ 1081 tcp_skb_pcount_set(skb, 1); 1082 TCP_SKB_CB(skb)->tcp_gso_size = 0; 1083 } else { 1084 tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now)); 1085 TCP_SKB_CB(skb)->tcp_gso_size = mss_now; 1086 } 1087 } 1088 1089 /* When a modification to fackets out becomes necessary, we need to check 1090 * skb is counted to fackets_out or not. 1091 */ 1092 static void tcp_adjust_fackets_out(struct sock *sk, const struct sk_buff *skb, 1093 int decr) 1094 { 1095 struct tcp_sock *tp = tcp_sk(sk); 1096 1097 if (!tp->sacked_out || tcp_is_reno(tp)) 1098 return; 1099 1100 if (after(tcp_highest_sack_seq(tp), TCP_SKB_CB(skb)->seq)) 1101 tp->fackets_out -= decr; 1102 } 1103 1104 /* Pcount in the middle of the write queue got changed, we need to do various 1105 * tweaks to fix counters 1106 */ 1107 static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int decr) 1108 { 1109 struct tcp_sock *tp = tcp_sk(sk); 1110 1111 tp->packets_out -= decr; 1112 1113 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 1114 tp->sacked_out -= decr; 1115 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) 1116 tp->retrans_out -= decr; 1117 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 1118 tp->lost_out -= decr; 1119 1120 /* Reno case is special. Sigh... */ 1121 if (tcp_is_reno(tp) && decr > 0) 1122 tp->sacked_out -= min_t(u32, tp->sacked_out, decr); 1123 1124 tcp_adjust_fackets_out(sk, skb, decr); 1125 1126 if (tp->lost_skb_hint && 1127 before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) && 1128 (tcp_is_fack(tp) || (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))) 1129 tp->lost_cnt_hint -= decr; 1130 1131 tcp_verify_left_out(tp); 1132 } 1133 1134 static bool tcp_has_tx_tstamp(const struct sk_buff *skb) 1135 { 1136 return TCP_SKB_CB(skb)->txstamp_ack || 1137 (skb_shinfo(skb)->tx_flags & SKBTX_ANY_TSTAMP); 1138 } 1139 1140 static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2) 1141 { 1142 struct skb_shared_info *shinfo = skb_shinfo(skb); 1143 1144 if (unlikely(tcp_has_tx_tstamp(skb)) && 1145 !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) { 1146 struct skb_shared_info *shinfo2 = skb_shinfo(skb2); 1147 u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP; 1148 1149 shinfo->tx_flags &= ~tsflags; 1150 shinfo2->tx_flags |= tsflags; 1151 swap(shinfo->tskey, shinfo2->tskey); 1152 TCP_SKB_CB(skb2)->txstamp_ack = TCP_SKB_CB(skb)->txstamp_ack; 1153 TCP_SKB_CB(skb)->txstamp_ack = 0; 1154 } 1155 } 1156 1157 static void tcp_skb_fragment_eor(struct sk_buff *skb, struct sk_buff *skb2) 1158 { 1159 TCP_SKB_CB(skb2)->eor = TCP_SKB_CB(skb)->eor; 1160 TCP_SKB_CB(skb)->eor = 0; 1161 } 1162 1163 /* Function to create two new TCP segments. Shrinks the given segment 1164 * to the specified size and appends a new segment with the rest of the 1165 * packet to the list. This won't be called frequently, I hope. 1166 * Remember, these are still headerless SKBs at this point. 1167 */ 1168 int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, 1169 unsigned int mss_now, gfp_t gfp) 1170 { 1171 struct tcp_sock *tp = tcp_sk(sk); 1172 struct sk_buff *buff; 1173 int nsize, old_factor; 1174 int nlen; 1175 u8 flags; 1176 1177 if (WARN_ON(len > skb->len)) 1178 return -EINVAL; 1179 1180 nsize = skb_headlen(skb) - len; 1181 if (nsize < 0) 1182 nsize = 0; 1183 1184 if (skb_unclone(skb, gfp)) 1185 return -ENOMEM; 1186 1187 /* Get a new skb... force flag on. */ 1188 buff = sk_stream_alloc_skb(sk, nsize, gfp, true); 1189 if (!buff) 1190 return -ENOMEM; /* We'll just try again later. */ 1191 1192 sk->sk_wmem_queued += buff->truesize; 1193 sk_mem_charge(sk, buff->truesize); 1194 nlen = skb->len - len - nsize; 1195 buff->truesize += nlen; 1196 skb->truesize -= nlen; 1197 1198 /* Correct the sequence numbers. */ 1199 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 1200 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 1201 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 1202 1203 /* PSH and FIN should only be set in the second packet. */ 1204 flags = TCP_SKB_CB(skb)->tcp_flags; 1205 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 1206 TCP_SKB_CB(buff)->tcp_flags = flags; 1207 TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked; 1208 tcp_skb_fragment_eor(skb, buff); 1209 1210 if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) { 1211 /* Copy and checksum data tail into the new buffer. */ 1212 buff->csum = csum_partial_copy_nocheck(skb->data + len, 1213 skb_put(buff, nsize), 1214 nsize, 0); 1215 1216 skb_trim(skb, len); 1217 1218 skb->csum = csum_block_sub(skb->csum, buff->csum, len); 1219 } else { 1220 skb->ip_summed = CHECKSUM_PARTIAL; 1221 skb_split(skb, buff, len); 1222 } 1223 1224 buff->ip_summed = skb->ip_summed; 1225 1226 buff->tstamp = skb->tstamp; 1227 tcp_fragment_tstamp(skb, buff); 1228 1229 old_factor = tcp_skb_pcount(skb); 1230 1231 /* Fix up tso_factor for both original and new SKB. */ 1232 tcp_set_skb_tso_segs(skb, mss_now); 1233 tcp_set_skb_tso_segs(buff, mss_now); 1234 1235 /* Update delivered info for the new segment */ 1236 TCP_SKB_CB(buff)->tx = TCP_SKB_CB(skb)->tx; 1237 1238 /* If this packet has been sent out already, we must 1239 * adjust the various packet counters. 1240 */ 1241 if (!before(tp->snd_nxt, TCP_SKB_CB(buff)->end_seq)) { 1242 int diff = old_factor - tcp_skb_pcount(skb) - 1243 tcp_skb_pcount(buff); 1244 1245 if (diff) 1246 tcp_adjust_pcount(sk, skb, diff); 1247 } 1248 1249 /* Link BUFF into the send queue. */ 1250 __skb_header_release(buff); 1251 tcp_insert_write_queue_after(skb, buff, sk); 1252 1253 return 0; 1254 } 1255 1256 /* This is similar to __pskb_pull_head() (it will go to core/skbuff.c 1257 * eventually). The difference is that pulled data not copied, but 1258 * immediately discarded. 1259 */ 1260 static void __pskb_trim_head(struct sk_buff *skb, int len) 1261 { 1262 struct skb_shared_info *shinfo; 1263 int i, k, eat; 1264 1265 eat = min_t(int, len, skb_headlen(skb)); 1266 if (eat) { 1267 __skb_pull(skb, eat); 1268 len -= eat; 1269 if (!len) 1270 return; 1271 } 1272 eat = len; 1273 k = 0; 1274 shinfo = skb_shinfo(skb); 1275 for (i = 0; i < shinfo->nr_frags; i++) { 1276 int size = skb_frag_size(&shinfo->frags[i]); 1277 1278 if (size <= eat) { 1279 skb_frag_unref(skb, i); 1280 eat -= size; 1281 } else { 1282 shinfo->frags[k] = shinfo->frags[i]; 1283 if (eat) { 1284 shinfo->frags[k].page_offset += eat; 1285 skb_frag_size_sub(&shinfo->frags[k], eat); 1286 eat = 0; 1287 } 1288 k++; 1289 } 1290 } 1291 shinfo->nr_frags = k; 1292 1293 skb_reset_tail_pointer(skb); 1294 skb->data_len -= len; 1295 skb->len = skb->data_len; 1296 } 1297 1298 /* Remove acked data from a packet in the transmit queue. */ 1299 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) 1300 { 1301 if (skb_unclone(skb, GFP_ATOMIC)) 1302 return -ENOMEM; 1303 1304 __pskb_trim_head(skb, len); 1305 1306 TCP_SKB_CB(skb)->seq += len; 1307 skb->ip_summed = CHECKSUM_PARTIAL; 1308 1309 skb->truesize -= len; 1310 sk->sk_wmem_queued -= len; 1311 sk_mem_uncharge(sk, len); 1312 sock_set_flag(sk, SOCK_QUEUE_SHRUNK); 1313 1314 /* Any change of skb->len requires recalculation of tso factor. */ 1315 if (tcp_skb_pcount(skb) > 1) 1316 tcp_set_skb_tso_segs(skb, tcp_skb_mss(skb)); 1317 1318 return 0; 1319 } 1320 1321 /* Calculate MSS not accounting any TCP options. */ 1322 static inline int __tcp_mtu_to_mss(struct sock *sk, int pmtu) 1323 { 1324 const struct tcp_sock *tp = tcp_sk(sk); 1325 const struct inet_connection_sock *icsk = inet_csk(sk); 1326 int mss_now; 1327 1328 /* Calculate base mss without TCP options: 1329 It is MMS_S - sizeof(tcphdr) of rfc1122 1330 */ 1331 mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr); 1332 1333 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1334 if (icsk->icsk_af_ops->net_frag_header_len) { 1335 const struct dst_entry *dst = __sk_dst_get(sk); 1336 1337 if (dst && dst_allfrag(dst)) 1338 mss_now -= icsk->icsk_af_ops->net_frag_header_len; 1339 } 1340 1341 /* Clamp it (mss_clamp does not include tcp options) */ 1342 if (mss_now > tp->rx_opt.mss_clamp) 1343 mss_now = tp->rx_opt.mss_clamp; 1344 1345 /* Now subtract optional transport overhead */ 1346 mss_now -= icsk->icsk_ext_hdr_len; 1347 1348 /* Then reserve room for full set of TCP options and 8 bytes of data */ 1349 if (mss_now < 48) 1350 mss_now = 48; 1351 return mss_now; 1352 } 1353 1354 /* Calculate MSS. Not accounting for SACKs here. */ 1355 int tcp_mtu_to_mss(struct sock *sk, int pmtu) 1356 { 1357 /* Subtract TCP options size, not including SACKs */ 1358 return __tcp_mtu_to_mss(sk, pmtu) - 1359 (tcp_sk(sk)->tcp_header_len - sizeof(struct tcphdr)); 1360 } 1361 1362 /* Inverse of above */ 1363 int tcp_mss_to_mtu(struct sock *sk, int mss) 1364 { 1365 const struct tcp_sock *tp = tcp_sk(sk); 1366 const struct inet_connection_sock *icsk = inet_csk(sk); 1367 int mtu; 1368 1369 mtu = mss + 1370 tp->tcp_header_len + 1371 icsk->icsk_ext_hdr_len + 1372 icsk->icsk_af_ops->net_header_len; 1373 1374 /* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */ 1375 if (icsk->icsk_af_ops->net_frag_header_len) { 1376 const struct dst_entry *dst = __sk_dst_get(sk); 1377 1378 if (dst && dst_allfrag(dst)) 1379 mtu += icsk->icsk_af_ops->net_frag_header_len; 1380 } 1381 return mtu; 1382 } 1383 EXPORT_SYMBOL(tcp_mss_to_mtu); 1384 1385 /* MTU probing init per socket */ 1386 void tcp_mtup_init(struct sock *sk) 1387 { 1388 struct tcp_sock *tp = tcp_sk(sk); 1389 struct inet_connection_sock *icsk = inet_csk(sk); 1390 struct net *net = sock_net(sk); 1391 1392 icsk->icsk_mtup.enabled = net->ipv4.sysctl_tcp_mtu_probing > 1; 1393 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + sizeof(struct tcphdr) + 1394 icsk->icsk_af_ops->net_header_len; 1395 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, net->ipv4.sysctl_tcp_base_mss); 1396 icsk->icsk_mtup.probe_size = 0; 1397 if (icsk->icsk_mtup.enabled) 1398 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 1399 } 1400 EXPORT_SYMBOL(tcp_mtup_init); 1401 1402 /* This function synchronize snd mss to current pmtu/exthdr set. 1403 1404 tp->rx_opt.user_mss is mss set by user by TCP_MAXSEG. It does NOT counts 1405 for TCP options, but includes only bare TCP header. 1406 1407 tp->rx_opt.mss_clamp is mss negotiated at connection setup. 1408 It is minimum of user_mss and mss received with SYN. 1409 It also does not include TCP options. 1410 1411 inet_csk(sk)->icsk_pmtu_cookie is last pmtu, seen by this function. 1412 1413 tp->mss_cache is current effective sending mss, including 1414 all tcp options except for SACKs. It is evaluated, 1415 taking into account current pmtu, but never exceeds 1416 tp->rx_opt.mss_clamp. 1417 1418 NOTE1. rfc1122 clearly states that advertised MSS 1419 DOES NOT include either tcp or ip options. 1420 1421 NOTE2. inet_csk(sk)->icsk_pmtu_cookie and tp->mss_cache 1422 are READ ONLY outside this function. --ANK (980731) 1423 */ 1424 unsigned int tcp_sync_mss(struct sock *sk, u32 pmtu) 1425 { 1426 struct tcp_sock *tp = tcp_sk(sk); 1427 struct inet_connection_sock *icsk = inet_csk(sk); 1428 int mss_now; 1429 1430 if (icsk->icsk_mtup.search_high > pmtu) 1431 icsk->icsk_mtup.search_high = pmtu; 1432 1433 mss_now = tcp_mtu_to_mss(sk, pmtu); 1434 mss_now = tcp_bound_to_half_wnd(tp, mss_now); 1435 1436 /* And store cached results */ 1437 icsk->icsk_pmtu_cookie = pmtu; 1438 if (icsk->icsk_mtup.enabled) 1439 mss_now = min(mss_now, tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)); 1440 tp->mss_cache = mss_now; 1441 1442 return mss_now; 1443 } 1444 EXPORT_SYMBOL(tcp_sync_mss); 1445 1446 /* Compute the current effective MSS, taking SACKs and IP options, 1447 * and even PMTU discovery events into account. 1448 */ 1449 unsigned int tcp_current_mss(struct sock *sk) 1450 { 1451 const struct tcp_sock *tp = tcp_sk(sk); 1452 const struct dst_entry *dst = __sk_dst_get(sk); 1453 u32 mss_now; 1454 unsigned int header_len; 1455 struct tcp_out_options opts; 1456 struct tcp_md5sig_key *md5; 1457 1458 mss_now = tp->mss_cache; 1459 1460 if (dst) { 1461 u32 mtu = dst_mtu(dst); 1462 if (mtu != inet_csk(sk)->icsk_pmtu_cookie) 1463 mss_now = tcp_sync_mss(sk, mtu); 1464 } 1465 1466 header_len = tcp_established_options(sk, NULL, &opts, &md5) + 1467 sizeof(struct tcphdr); 1468 /* The mss_cache is sized based on tp->tcp_header_len, which assumes 1469 * some common options. If this is an odd packet (because we have SACK 1470 * blocks etc) then our calculated header_len will be different, and 1471 * we have to adjust mss_now correspondingly */ 1472 if (header_len != tp->tcp_header_len) { 1473 int delta = (int) header_len - tp->tcp_header_len; 1474 mss_now -= delta; 1475 } 1476 1477 return mss_now; 1478 } 1479 1480 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto. 1481 * As additional protections, we do not touch cwnd in retransmission phases, 1482 * and if application hit its sndbuf limit recently. 1483 */ 1484 static void tcp_cwnd_application_limited(struct sock *sk) 1485 { 1486 struct tcp_sock *tp = tcp_sk(sk); 1487 1488 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open && 1489 sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { 1490 /* Limited by application or receiver window. */ 1491 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk)); 1492 u32 win_used = max(tp->snd_cwnd_used, init_win); 1493 if (win_used < tp->snd_cwnd) { 1494 tp->snd_ssthresh = tcp_current_ssthresh(sk); 1495 tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1; 1496 } 1497 tp->snd_cwnd_used = 0; 1498 } 1499 tp->snd_cwnd_stamp = tcp_time_stamp; 1500 } 1501 1502 static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited) 1503 { 1504 struct tcp_sock *tp = tcp_sk(sk); 1505 1506 /* Track the maximum number of outstanding packets in each 1507 * window, and remember whether we were cwnd-limited then. 1508 */ 1509 if (!before(tp->snd_una, tp->max_packets_seq) || 1510 tp->packets_out > tp->max_packets_out) { 1511 tp->max_packets_out = tp->packets_out; 1512 tp->max_packets_seq = tp->snd_nxt; 1513 tp->is_cwnd_limited = is_cwnd_limited; 1514 } 1515 1516 if (tcp_is_cwnd_limited(sk)) { 1517 /* Network is feed fully. */ 1518 tp->snd_cwnd_used = 0; 1519 tp->snd_cwnd_stamp = tcp_time_stamp; 1520 } else { 1521 /* Network starves. */ 1522 if (tp->packets_out > tp->snd_cwnd_used) 1523 tp->snd_cwnd_used = tp->packets_out; 1524 1525 if (sysctl_tcp_slow_start_after_idle && 1526 (s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto) 1527 tcp_cwnd_application_limited(sk); 1528 1529 /* The following conditions together indicate the starvation 1530 * is caused by insufficient sender buffer: 1531 * 1) just sent some data (see tcp_write_xmit) 1532 * 2) not cwnd limited (this else condition) 1533 * 3) no more data to send (null tcp_send_head ) 1534 * 4) application is hitting buffer limit (SOCK_NOSPACE) 1535 */ 1536 if (!tcp_send_head(sk) && sk->sk_socket && 1537 test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) && 1538 (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) 1539 tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED); 1540 } 1541 } 1542 1543 /* Minshall's variant of the Nagle send check. */ 1544 static bool tcp_minshall_check(const struct tcp_sock *tp) 1545 { 1546 return after(tp->snd_sml, tp->snd_una) && 1547 !after(tp->snd_sml, tp->snd_nxt); 1548 } 1549 1550 /* Update snd_sml if this skb is under mss 1551 * Note that a TSO packet might end with a sub-mss segment 1552 * The test is really : 1553 * if ((skb->len % mss) != 0) 1554 * tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1555 * But we can avoid doing the divide again given we already have 1556 * skb_pcount = skb->len / mss_now 1557 */ 1558 static void tcp_minshall_update(struct tcp_sock *tp, unsigned int mss_now, 1559 const struct sk_buff *skb) 1560 { 1561 if (skb->len < tcp_skb_pcount(skb) * mss_now) 1562 tp->snd_sml = TCP_SKB_CB(skb)->end_seq; 1563 } 1564 1565 /* Return false, if packet can be sent now without violation Nagle's rules: 1566 * 1. It is full sized. (provided by caller in %partial bool) 1567 * 2. Or it contains FIN. (already checked by caller) 1568 * 3. Or TCP_CORK is not set, and TCP_NODELAY is set. 1569 * 4. Or TCP_CORK is not set, and all sent packets are ACKed. 1570 * With Minshall's modification: all sent small packets are ACKed. 1571 */ 1572 static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp, 1573 int nonagle) 1574 { 1575 return partial && 1576 ((nonagle & TCP_NAGLE_CORK) || 1577 (!nonagle && tp->packets_out && tcp_minshall_check(tp))); 1578 } 1579 1580 /* Return how many segs we'd like on a TSO packet, 1581 * to send one TSO packet per ms 1582 */ 1583 u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now, 1584 int min_tso_segs) 1585 { 1586 u32 bytes, segs; 1587 1588 bytes = min(sk->sk_pacing_rate >> 10, 1589 sk->sk_gso_max_size - 1 - MAX_TCP_HEADER); 1590 1591 /* Goal is to send at least one packet per ms, 1592 * not one big TSO packet every 100 ms. 1593 * This preserves ACK clocking and is consistent 1594 * with tcp_tso_should_defer() heuristic. 1595 */ 1596 segs = max_t(u32, bytes / mss_now, min_tso_segs); 1597 1598 return min_t(u32, segs, sk->sk_gso_max_segs); 1599 } 1600 EXPORT_SYMBOL(tcp_tso_autosize); 1601 1602 /* Return the number of segments we want in the skb we are transmitting. 1603 * See if congestion control module wants to decide; otherwise, autosize. 1604 */ 1605 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now) 1606 { 1607 const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; 1608 u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0; 1609 1610 return tso_segs ? : 1611 tcp_tso_autosize(sk, mss_now, sysctl_tcp_min_tso_segs); 1612 } 1613 1614 /* Returns the portion of skb which can be sent right away */ 1615 static unsigned int tcp_mss_split_point(const struct sock *sk, 1616 const struct sk_buff *skb, 1617 unsigned int mss_now, 1618 unsigned int max_segs, 1619 int nonagle) 1620 { 1621 const struct tcp_sock *tp = tcp_sk(sk); 1622 u32 partial, needed, window, max_len; 1623 1624 window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 1625 max_len = mss_now * max_segs; 1626 1627 if (likely(max_len <= window && skb != tcp_write_queue_tail(sk))) 1628 return max_len; 1629 1630 needed = min(skb->len, window); 1631 1632 if (max_len <= needed) 1633 return max_len; 1634 1635 partial = needed % mss_now; 1636 /* If last segment is not a full MSS, check if Nagle rules allow us 1637 * to include this last segment in this skb. 1638 * Otherwise, we'll split the skb at last MSS boundary 1639 */ 1640 if (tcp_nagle_check(partial != 0, tp, nonagle)) 1641 return needed - partial; 1642 1643 return needed; 1644 } 1645 1646 /* Can at least one segment of SKB be sent right now, according to the 1647 * congestion window rules? If so, return how many segments are allowed. 1648 */ 1649 static inline unsigned int tcp_cwnd_test(const struct tcp_sock *tp, 1650 const struct sk_buff *skb) 1651 { 1652 u32 in_flight, cwnd, halfcwnd; 1653 1654 /* Don't be strict about the congestion window for the final FIN. */ 1655 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) && 1656 tcp_skb_pcount(skb) == 1) 1657 return 1; 1658 1659 in_flight = tcp_packets_in_flight(tp); 1660 cwnd = tp->snd_cwnd; 1661 if (in_flight >= cwnd) 1662 return 0; 1663 1664 /* For better scheduling, ensure we have at least 1665 * 2 GSO packets in flight. 1666 */ 1667 halfcwnd = max(cwnd >> 1, 1U); 1668 return min(halfcwnd, cwnd - in_flight); 1669 } 1670 1671 /* Initialize TSO state of a skb. 1672 * This must be invoked the first time we consider transmitting 1673 * SKB onto the wire. 1674 */ 1675 static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now) 1676 { 1677 int tso_segs = tcp_skb_pcount(skb); 1678 1679 if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) { 1680 tcp_set_skb_tso_segs(skb, mss_now); 1681 tso_segs = tcp_skb_pcount(skb); 1682 } 1683 return tso_segs; 1684 } 1685 1686 1687 /* Return true if the Nagle test allows this packet to be 1688 * sent now. 1689 */ 1690 static inline bool tcp_nagle_test(const struct tcp_sock *tp, const struct sk_buff *skb, 1691 unsigned int cur_mss, int nonagle) 1692 { 1693 /* Nagle rule does not apply to frames, which sit in the middle of the 1694 * write_queue (they have no chances to get new data). 1695 * 1696 * This is implemented in the callers, where they modify the 'nonagle' 1697 * argument based upon the location of SKB in the send queue. 1698 */ 1699 if (nonagle & TCP_NAGLE_PUSH) 1700 return true; 1701 1702 /* Don't use the nagle rule for urgent data (or for the final FIN). */ 1703 if (tcp_urg_mode(tp) || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)) 1704 return true; 1705 1706 if (!tcp_nagle_check(skb->len < cur_mss, tp, nonagle)) 1707 return true; 1708 1709 return false; 1710 } 1711 1712 /* Does at least the first segment of SKB fit into the send window? */ 1713 static bool tcp_snd_wnd_test(const struct tcp_sock *tp, 1714 const struct sk_buff *skb, 1715 unsigned int cur_mss) 1716 { 1717 u32 end_seq = TCP_SKB_CB(skb)->end_seq; 1718 1719 if (skb->len > cur_mss) 1720 end_seq = TCP_SKB_CB(skb)->seq + cur_mss; 1721 1722 return !after(end_seq, tcp_wnd_end(tp)); 1723 } 1724 1725 /* This checks if the data bearing packet SKB (usually tcp_send_head(sk)) 1726 * should be put on the wire right now. If so, it returns the number of 1727 * packets allowed by the congestion window. 1728 */ 1729 static unsigned int tcp_snd_test(const struct sock *sk, struct sk_buff *skb, 1730 unsigned int cur_mss, int nonagle) 1731 { 1732 const struct tcp_sock *tp = tcp_sk(sk); 1733 unsigned int cwnd_quota; 1734 1735 tcp_init_tso_segs(skb, cur_mss); 1736 1737 if (!tcp_nagle_test(tp, skb, cur_mss, nonagle)) 1738 return 0; 1739 1740 cwnd_quota = tcp_cwnd_test(tp, skb); 1741 if (cwnd_quota && !tcp_snd_wnd_test(tp, skb, cur_mss)) 1742 cwnd_quota = 0; 1743 1744 return cwnd_quota; 1745 } 1746 1747 /* Test if sending is allowed right now. */ 1748 bool tcp_may_send_now(struct sock *sk) 1749 { 1750 const struct tcp_sock *tp = tcp_sk(sk); 1751 struct sk_buff *skb = tcp_send_head(sk); 1752 1753 return skb && 1754 tcp_snd_test(sk, skb, tcp_current_mss(sk), 1755 (tcp_skb_is_last(sk, skb) ? 1756 tp->nonagle : TCP_NAGLE_PUSH)); 1757 } 1758 1759 /* Trim TSO SKB to LEN bytes, put the remaining data into a new packet 1760 * which is put after SKB on the list. It is very much like 1761 * tcp_fragment() except that it may make several kinds of assumptions 1762 * in order to speed up the splitting operation. In particular, we 1763 * know that all the data is in scatter-gather pages, and that the 1764 * packet has never been sent out before (and thus is not cloned). 1765 */ 1766 static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, 1767 unsigned int mss_now, gfp_t gfp) 1768 { 1769 struct sk_buff *buff; 1770 int nlen = skb->len - len; 1771 u8 flags; 1772 1773 /* All of a TSO frame must be composed of paged data. */ 1774 if (skb->len != skb->data_len) 1775 return tcp_fragment(sk, skb, len, mss_now, gfp); 1776 1777 buff = sk_stream_alloc_skb(sk, 0, gfp, true); 1778 if (unlikely(!buff)) 1779 return -ENOMEM; 1780 1781 sk->sk_wmem_queued += buff->truesize; 1782 sk_mem_charge(sk, buff->truesize); 1783 buff->truesize += nlen; 1784 skb->truesize -= nlen; 1785 1786 /* Correct the sequence numbers. */ 1787 TCP_SKB_CB(buff)->seq = TCP_SKB_CB(skb)->seq + len; 1788 TCP_SKB_CB(buff)->end_seq = TCP_SKB_CB(skb)->end_seq; 1789 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(buff)->seq; 1790 1791 /* PSH and FIN should only be set in the second packet. */ 1792 flags = TCP_SKB_CB(skb)->tcp_flags; 1793 TCP_SKB_CB(skb)->tcp_flags = flags & ~(TCPHDR_FIN | TCPHDR_PSH); 1794 TCP_SKB_CB(buff)->tcp_flags = flags; 1795 1796 /* This packet was never sent out yet, so no SACK bits. */ 1797 TCP_SKB_CB(buff)->sacked = 0; 1798 1799 tcp_skb_fragment_eor(skb, buff); 1800 1801 buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL; 1802 skb_split(skb, buff, len); 1803 tcp_fragment_tstamp(skb, buff); 1804 1805 /* Fix up tso_factor for both original and new SKB. */ 1806 tcp_set_skb_tso_segs(skb, mss_now); 1807 tcp_set_skb_tso_segs(buff, mss_now); 1808 1809 /* Link BUFF into the send queue. */ 1810 __skb_header_release(buff); 1811 tcp_insert_write_queue_after(skb, buff, sk); 1812 1813 return 0; 1814 } 1815 1816 /* Try to defer sending, if possible, in order to minimize the amount 1817 * of TSO splitting we do. View it as a kind of TSO Nagle test. 1818 * 1819 * This algorithm is from John Heffner. 1820 */ 1821 static bool tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb, 1822 bool *is_cwnd_limited, u32 max_segs) 1823 { 1824 const struct inet_connection_sock *icsk = inet_csk(sk); 1825 u32 age, send_win, cong_win, limit, in_flight; 1826 struct tcp_sock *tp = tcp_sk(sk); 1827 struct skb_mstamp now; 1828 struct sk_buff *head; 1829 int win_divisor; 1830 1831 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) 1832 goto send_now; 1833 1834 if (icsk->icsk_ca_state >= TCP_CA_Recovery) 1835 goto send_now; 1836 1837 /* Avoid bursty behavior by allowing defer 1838 * only if the last write was recent. 1839 */ 1840 if ((s32)(tcp_time_stamp - tp->lsndtime) > 0) 1841 goto send_now; 1842 1843 in_flight = tcp_packets_in_flight(tp); 1844 1845 BUG_ON(tcp_skb_pcount(skb) <= 1 || (tp->snd_cwnd <= in_flight)); 1846 1847 send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 1848 1849 /* From in_flight test above, we know that cwnd > in_flight. */ 1850 cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache; 1851 1852 limit = min(send_win, cong_win); 1853 1854 /* If a full-sized TSO skb can be sent, do it. */ 1855 if (limit >= max_segs * tp->mss_cache) 1856 goto send_now; 1857 1858 /* Middle in queue won't get any more data, full sendable already? */ 1859 if ((skb != tcp_write_queue_tail(sk)) && (limit >= skb->len)) 1860 goto send_now; 1861 1862 win_divisor = ACCESS_ONCE(sysctl_tcp_tso_win_divisor); 1863 if (win_divisor) { 1864 u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache); 1865 1866 /* If at least some fraction of a window is available, 1867 * just use it. 1868 */ 1869 chunk /= win_divisor; 1870 if (limit >= chunk) 1871 goto send_now; 1872 } else { 1873 /* Different approach, try not to defer past a single 1874 * ACK. Receiver should ACK every other full sized 1875 * frame, so if we have space for more than 3 frames 1876 * then send now. 1877 */ 1878 if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache) 1879 goto send_now; 1880 } 1881 1882 head = tcp_write_queue_head(sk); 1883 skb_mstamp_get(&now); 1884 age = skb_mstamp_us_delta(&now, &head->skb_mstamp); 1885 /* If next ACK is likely to come too late (half srtt), do not defer */ 1886 if (age < (tp->srtt_us >> 4)) 1887 goto send_now; 1888 1889 /* Ok, it looks like it is advisable to defer. */ 1890 1891 if (cong_win < send_win && cong_win <= skb->len) 1892 *is_cwnd_limited = true; 1893 1894 return true; 1895 1896 send_now: 1897 return false; 1898 } 1899 1900 static inline void tcp_mtu_check_reprobe(struct sock *sk) 1901 { 1902 struct inet_connection_sock *icsk = inet_csk(sk); 1903 struct tcp_sock *tp = tcp_sk(sk); 1904 struct net *net = sock_net(sk); 1905 u32 interval; 1906 s32 delta; 1907 1908 interval = net->ipv4.sysctl_tcp_probe_interval; 1909 delta = tcp_time_stamp - icsk->icsk_mtup.probe_timestamp; 1910 if (unlikely(delta >= interval * HZ)) { 1911 int mss = tcp_current_mss(sk); 1912 1913 /* Update current search range */ 1914 icsk->icsk_mtup.probe_size = 0; 1915 icsk->icsk_mtup.search_high = tp->rx_opt.mss_clamp + 1916 sizeof(struct tcphdr) + 1917 icsk->icsk_af_ops->net_header_len; 1918 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 1919 1920 /* Update probe time stamp */ 1921 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 1922 } 1923 } 1924 1925 /* Create a new MTU probe if we are ready. 1926 * MTU probe is regularly attempting to increase the path MTU by 1927 * deliberately sending larger packets. This discovers routing 1928 * changes resulting in larger path MTUs. 1929 * 1930 * Returns 0 if we should wait to probe (no cwnd available), 1931 * 1 if a probe was sent, 1932 * -1 otherwise 1933 */ 1934 static int tcp_mtu_probe(struct sock *sk) 1935 { 1936 struct inet_connection_sock *icsk = inet_csk(sk); 1937 struct tcp_sock *tp = tcp_sk(sk); 1938 struct sk_buff *skb, *nskb, *next; 1939 struct net *net = sock_net(sk); 1940 int probe_size; 1941 int size_needed; 1942 int copy, len; 1943 int mss_now; 1944 int interval; 1945 1946 /* Not currently probing/verifying, 1947 * not in recovery, 1948 * have enough cwnd, and 1949 * not SACKing (the variable headers throw things off) 1950 */ 1951 if (likely(!icsk->icsk_mtup.enabled || 1952 icsk->icsk_mtup.probe_size || 1953 inet_csk(sk)->icsk_ca_state != TCP_CA_Open || 1954 tp->snd_cwnd < 11 || 1955 tp->rx_opt.num_sacks || tp->rx_opt.dsack)) 1956 return -1; 1957 1958 /* Use binary search for probe_size between tcp_mss_base, 1959 * and current mss_clamp. if (search_high - search_low) 1960 * smaller than a threshold, backoff from probing. 1961 */ 1962 mss_now = tcp_current_mss(sk); 1963 probe_size = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high + 1964 icsk->icsk_mtup.search_low) >> 1); 1965 size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; 1966 interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low; 1967 /* When misfortune happens, we are reprobing actively, 1968 * and then reprobe timer has expired. We stick with current 1969 * probing process by not resetting search range to its orignal. 1970 */ 1971 if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) || 1972 interval < net->ipv4.sysctl_tcp_probe_threshold) { 1973 /* Check whether enough time has elaplased for 1974 * another round of probing. 1975 */ 1976 tcp_mtu_check_reprobe(sk); 1977 return -1; 1978 } 1979 1980 /* Have enough data in the send queue to probe? */ 1981 if (tp->write_seq - tp->snd_nxt < size_needed) 1982 return -1; 1983 1984 if (tp->snd_wnd < size_needed) 1985 return -1; 1986 if (after(tp->snd_nxt + size_needed, tcp_wnd_end(tp))) 1987 return 0; 1988 1989 /* Do we need to wait to drain cwnd? With none in flight, don't stall */ 1990 if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) { 1991 if (!tcp_packets_in_flight(tp)) 1992 return -1; 1993 else 1994 return 0; 1995 } 1996 1997 /* We're allowed to probe. Build it now. */ 1998 nskb = sk_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false); 1999 if (!nskb) 2000 return -1; 2001 sk->sk_wmem_queued += nskb->truesize; 2002 sk_mem_charge(sk, nskb->truesize); 2003 2004 skb = tcp_send_head(sk); 2005 2006 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq; 2007 TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size; 2008 TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK; 2009 TCP_SKB_CB(nskb)->sacked = 0; 2010 nskb->csum = 0; 2011 nskb->ip_summed = skb->ip_summed; 2012 2013 tcp_insert_write_queue_before(nskb, skb, sk); 2014 2015 len = 0; 2016 tcp_for_write_queue_from_safe(skb, next, sk) { 2017 copy = min_t(int, skb->len, probe_size - len); 2018 if (nskb->ip_summed) { 2019 skb_copy_bits(skb, 0, skb_put(nskb, copy), copy); 2020 } else { 2021 __wsum csum = skb_copy_and_csum_bits(skb, 0, 2022 skb_put(nskb, copy), 2023 copy, 0); 2024 nskb->csum = csum_block_add(nskb->csum, csum, len); 2025 } 2026 2027 if (skb->len <= copy) { 2028 /* We've eaten all the data from this skb. 2029 * Throw it away. */ 2030 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; 2031 tcp_unlink_write_queue(skb, sk); 2032 sk_wmem_free_skb(sk, skb); 2033 } else { 2034 TCP_SKB_CB(nskb)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags & 2035 ~(TCPHDR_FIN|TCPHDR_PSH); 2036 if (!skb_shinfo(skb)->nr_frags) { 2037 skb_pull(skb, copy); 2038 if (skb->ip_summed != CHECKSUM_PARTIAL) 2039 skb->csum = csum_partial(skb->data, 2040 skb->len, 0); 2041 } else { 2042 __pskb_trim_head(skb, copy); 2043 tcp_set_skb_tso_segs(skb, mss_now); 2044 } 2045 TCP_SKB_CB(skb)->seq += copy; 2046 } 2047 2048 len += copy; 2049 2050 if (len >= probe_size) 2051 break; 2052 } 2053 tcp_init_tso_segs(nskb, nskb->len); 2054 2055 /* We're ready to send. If this fails, the probe will 2056 * be resegmented into mss-sized pieces by tcp_write_xmit(). 2057 */ 2058 if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) { 2059 /* Decrement cwnd here because we are sending 2060 * effectively two packets. */ 2061 tp->snd_cwnd--; 2062 tcp_event_new_data_sent(sk, nskb); 2063 2064 icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len); 2065 tp->mtu_probe.probe_seq_start = TCP_SKB_CB(nskb)->seq; 2066 tp->mtu_probe.probe_seq_end = TCP_SKB_CB(nskb)->end_seq; 2067 2068 return 1; 2069 } 2070 2071 return -1; 2072 } 2073 2074 /* TCP Small Queues : 2075 * Control number of packets in qdisc/devices to two packets / or ~1 ms. 2076 * (These limits are doubled for retransmits) 2077 * This allows for : 2078 * - better RTT estimation and ACK scheduling 2079 * - faster recovery 2080 * - high rates 2081 * Alas, some drivers / subsystems require a fair amount 2082 * of queued bytes to ensure line rate. 2083 * One example is wifi aggregation (802.11 AMPDU) 2084 */ 2085 static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb, 2086 unsigned int factor) 2087 { 2088 unsigned int limit; 2089 2090 limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 10); 2091 limit = min_t(u32, limit, sysctl_tcp_limit_output_bytes); 2092 limit <<= factor; 2093 2094 if (atomic_read(&sk->sk_wmem_alloc) > limit) { 2095 /* Always send the 1st or 2nd skb in write queue. 2096 * No need to wait for TX completion to call us back, 2097 * after softirq/tasklet schedule. 2098 * This helps when TX completions are delayed too much. 2099 */ 2100 if (skb == sk->sk_write_queue.next || 2101 skb->prev == sk->sk_write_queue.next) 2102 return false; 2103 2104 set_bit(TSQ_THROTTLED, &sk->sk_tsq_flags); 2105 /* It is possible TX completion already happened 2106 * before we set TSQ_THROTTLED, so we must 2107 * test again the condition. 2108 */ 2109 smp_mb__after_atomic(); 2110 if (atomic_read(&sk->sk_wmem_alloc) > limit) 2111 return true; 2112 } 2113 return false; 2114 } 2115 2116 static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new) 2117 { 2118 const u32 now = tcp_time_stamp; 2119 2120 if (tp->chrono_type > TCP_CHRONO_UNSPEC) 2121 tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start; 2122 tp->chrono_start = now; 2123 tp->chrono_type = new; 2124 } 2125 2126 void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type) 2127 { 2128 struct tcp_sock *tp = tcp_sk(sk); 2129 2130 /* If there are multiple conditions worthy of tracking in a 2131 * chronograph then the highest priority enum takes precedence 2132 * over the other conditions. So that if something "more interesting" 2133 * starts happening, stop the previous chrono and start a new one. 2134 */ 2135 if (type > tp->chrono_type) 2136 tcp_chrono_set(tp, type); 2137 } 2138 2139 void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type) 2140 { 2141 struct tcp_sock *tp = tcp_sk(sk); 2142 2143 2144 /* There are multiple conditions worthy of tracking in a 2145 * chronograph, so that the highest priority enum takes 2146 * precedence over the other conditions (see tcp_chrono_start). 2147 * If a condition stops, we only stop chrono tracking if 2148 * it's the "most interesting" or current chrono we are 2149 * tracking and starts busy chrono if we have pending data. 2150 */ 2151 if (tcp_write_queue_empty(sk)) 2152 tcp_chrono_set(tp, TCP_CHRONO_UNSPEC); 2153 else if (type == tp->chrono_type) 2154 tcp_chrono_set(tp, TCP_CHRONO_BUSY); 2155 } 2156 2157 /* This routine writes packets to the network. It advances the 2158 * send_head. This happens as incoming acks open up the remote 2159 * window for us. 2160 * 2161 * LARGESEND note: !tcp_urg_mode is overkill, only frames between 2162 * snd_up-64k-mss .. snd_up cannot be large. However, taking into 2163 * account rare use of URG, this is not a big flaw. 2164 * 2165 * Send at most one packet when push_one > 0. Temporarily ignore 2166 * cwnd limit to force at most one packet out when push_one == 2. 2167 2168 * Returns true, if no segments are in flight and we have queued segments, 2169 * but cannot send anything now because of SWS or another problem. 2170 */ 2171 static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle, 2172 int push_one, gfp_t gfp) 2173 { 2174 struct tcp_sock *tp = tcp_sk(sk); 2175 struct sk_buff *skb; 2176 unsigned int tso_segs, sent_pkts; 2177 int cwnd_quota; 2178 int result; 2179 bool is_cwnd_limited = false, is_rwnd_limited = false; 2180 u32 max_segs; 2181 2182 sent_pkts = 0; 2183 2184 if (!push_one) { 2185 /* Do MTU probing. */ 2186 result = tcp_mtu_probe(sk); 2187 if (!result) { 2188 return false; 2189 } else if (result > 0) { 2190 sent_pkts = 1; 2191 } 2192 } 2193 2194 max_segs = tcp_tso_segs(sk, mss_now); 2195 while ((skb = tcp_send_head(sk))) { 2196 unsigned int limit; 2197 2198 tso_segs = tcp_init_tso_segs(skb, mss_now); 2199 BUG_ON(!tso_segs); 2200 2201 if (unlikely(tp->repair) && tp->repair_queue == TCP_SEND_QUEUE) { 2202 /* "skb_mstamp" is used as a start point for the retransmit timer */ 2203 skb_mstamp_get(&skb->skb_mstamp); 2204 goto repair; /* Skip network transmission */ 2205 } 2206 2207 cwnd_quota = tcp_cwnd_test(tp, skb); 2208 if (!cwnd_quota) { 2209 if (push_one == 2) 2210 /* Force out a loss probe pkt. */ 2211 cwnd_quota = 1; 2212 else 2213 break; 2214 } 2215 2216 if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) { 2217 is_rwnd_limited = true; 2218 break; 2219 } 2220 2221 if (tso_segs == 1) { 2222 if (unlikely(!tcp_nagle_test(tp, skb, mss_now, 2223 (tcp_skb_is_last(sk, skb) ? 2224 nonagle : TCP_NAGLE_PUSH)))) 2225 break; 2226 } else { 2227 if (!push_one && 2228 tcp_tso_should_defer(sk, skb, &is_cwnd_limited, 2229 max_segs)) 2230 break; 2231 } 2232 2233 limit = mss_now; 2234 if (tso_segs > 1 && !tcp_urg_mode(tp)) 2235 limit = tcp_mss_split_point(sk, skb, mss_now, 2236 min_t(unsigned int, 2237 cwnd_quota, 2238 max_segs), 2239 nonagle); 2240 2241 if (skb->len > limit && 2242 unlikely(tso_fragment(sk, skb, limit, mss_now, gfp))) 2243 break; 2244 2245 if (test_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags)) 2246 clear_bit(TCP_TSQ_DEFERRED, &sk->sk_tsq_flags); 2247 if (tcp_small_queue_check(sk, skb, 0)) 2248 break; 2249 2250 if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp))) 2251 break; 2252 2253 repair: 2254 /* Advance the send_head. This one is sent out. 2255 * This call will increment packets_out. 2256 */ 2257 tcp_event_new_data_sent(sk, skb); 2258 2259 tcp_minshall_update(tp, mss_now, skb); 2260 sent_pkts += tcp_skb_pcount(skb); 2261 2262 if (push_one) 2263 break; 2264 } 2265 2266 if (is_rwnd_limited) 2267 tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED); 2268 else 2269 tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED); 2270 2271 if (likely(sent_pkts)) { 2272 if (tcp_in_cwnd_reduction(sk)) 2273 tp->prr_out += sent_pkts; 2274 2275 /* Send one loss probe per tail loss episode. */ 2276 if (push_one != 2) 2277 tcp_schedule_loss_probe(sk); 2278 is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd); 2279 tcp_cwnd_validate(sk, is_cwnd_limited); 2280 return false; 2281 } 2282 return !tp->packets_out && tcp_send_head(sk); 2283 } 2284 2285 bool tcp_schedule_loss_probe(struct sock *sk) 2286 { 2287 struct inet_connection_sock *icsk = inet_csk(sk); 2288 struct tcp_sock *tp = tcp_sk(sk); 2289 u32 timeout, tlp_time_stamp, rto_time_stamp; 2290 u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3); 2291 2292 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS)) 2293 return false; 2294 /* No consecutive loss probes. */ 2295 if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) { 2296 tcp_rearm_rto(sk); 2297 return false; 2298 } 2299 /* Don't do any loss probe on a Fast Open connection before 3WHS 2300 * finishes. 2301 */ 2302 if (tp->fastopen_rsk) 2303 return false; 2304 2305 /* TLP is only scheduled when next timer event is RTO. */ 2306 if (icsk->icsk_pending != ICSK_TIME_RETRANS) 2307 return false; 2308 2309 /* Schedule a loss probe in 2*RTT for SACK capable connections 2310 * in Open state, that are either limited by cwnd or application. 2311 */ 2312 if (sysctl_tcp_early_retrans < 3 || !tp->packets_out || 2313 !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open) 2314 return false; 2315 2316 if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) && 2317 tcp_send_head(sk)) 2318 return false; 2319 2320 /* Probe timeout is at least 1.5*rtt + TCP_DELACK_MAX to account 2321 * for delayed ack when there's one outstanding packet. If no RTT 2322 * sample is available then probe after TCP_TIMEOUT_INIT. 2323 */ 2324 timeout = rtt << 1 ? : TCP_TIMEOUT_INIT; 2325 if (tp->packets_out == 1) 2326 timeout = max_t(u32, timeout, 2327 (rtt + (rtt >> 1) + TCP_DELACK_MAX)); 2328 timeout = max_t(u32, timeout, msecs_to_jiffies(10)); 2329 2330 /* If RTO is shorter, just schedule TLP in its place. */ 2331 tlp_time_stamp = tcp_time_stamp + timeout; 2332 rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout; 2333 if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) { 2334 s32 delta = rto_time_stamp - tcp_time_stamp; 2335 if (delta > 0) 2336 timeout = delta; 2337 } 2338 2339 inet_csk_reset_xmit_timer(sk, ICSK_TIME_LOSS_PROBE, timeout, 2340 TCP_RTO_MAX); 2341 return true; 2342 } 2343 2344 /* Thanks to skb fast clones, we can detect if a prior transmit of 2345 * a packet is still in a qdisc or driver queue. 2346 * In this case, there is very little point doing a retransmit ! 2347 */ 2348 static bool skb_still_in_host_queue(const struct sock *sk, 2349 const struct sk_buff *skb) 2350 { 2351 if (unlikely(skb_fclone_busy(sk, skb))) { 2352 NET_INC_STATS(sock_net(sk), 2353 LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES); 2354 return true; 2355 } 2356 return false; 2357 } 2358 2359 /* When probe timeout (PTO) fires, try send a new segment if possible, else 2360 * retransmit the last segment. 2361 */ 2362 void tcp_send_loss_probe(struct sock *sk) 2363 { 2364 struct tcp_sock *tp = tcp_sk(sk); 2365 struct sk_buff *skb; 2366 int pcount; 2367 int mss = tcp_current_mss(sk); 2368 2369 skb = tcp_send_head(sk); 2370 if (skb) { 2371 if (tcp_snd_wnd_test(tp, skb, mss)) { 2372 pcount = tp->packets_out; 2373 tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC); 2374 if (tp->packets_out > pcount) 2375 goto probe_sent; 2376 goto rearm_timer; 2377 } 2378 skb = tcp_write_queue_prev(sk, skb); 2379 } else { 2380 skb = tcp_write_queue_tail(sk); 2381 } 2382 2383 /* At most one outstanding TLP retransmission. */ 2384 if (tp->tlp_high_seq) 2385 goto rearm_timer; 2386 2387 /* Retransmit last segment. */ 2388 if (WARN_ON(!skb)) 2389 goto rearm_timer; 2390 2391 if (skb_still_in_host_queue(sk, skb)) 2392 goto rearm_timer; 2393 2394 pcount = tcp_skb_pcount(skb); 2395 if (WARN_ON(!pcount)) 2396 goto rearm_timer; 2397 2398 if ((pcount > 1) && (skb->len > (pcount - 1) * mss)) { 2399 if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss, 2400 GFP_ATOMIC))) 2401 goto rearm_timer; 2402 skb = tcp_write_queue_next(sk, skb); 2403 } 2404 2405 if (WARN_ON(!skb || !tcp_skb_pcount(skb))) 2406 goto rearm_timer; 2407 2408 if (__tcp_retransmit_skb(sk, skb, 1)) 2409 goto rearm_timer; 2410 2411 /* Record snd_nxt for loss detection. */ 2412 tp->tlp_high_seq = tp->snd_nxt; 2413 2414 probe_sent: 2415 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSPROBES); 2416 /* Reset s.t. tcp_rearm_rto will restart timer from now */ 2417 inet_csk(sk)->icsk_pending = 0; 2418 rearm_timer: 2419 tcp_rearm_rto(sk); 2420 } 2421 2422 /* Push out any pending frames which were held back due to 2423 * TCP_CORK or attempt at coalescing tiny packets. 2424 * The socket must be locked by the caller. 2425 */ 2426 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss, 2427 int nonagle) 2428 { 2429 /* If we are closed, the bytes will have to remain here. 2430 * In time closedown will finish, we empty the write queue and 2431 * all will be happy. 2432 */ 2433 if (unlikely(sk->sk_state == TCP_CLOSE)) 2434 return; 2435 2436 if (tcp_write_xmit(sk, cur_mss, nonagle, 0, 2437 sk_gfp_mask(sk, GFP_ATOMIC))) 2438 tcp_check_probe_timer(sk); 2439 } 2440 2441 /* Send _single_ skb sitting at the send head. This function requires 2442 * true push pending frames to setup probe timer etc. 2443 */ 2444 void tcp_push_one(struct sock *sk, unsigned int mss_now) 2445 { 2446 struct sk_buff *skb = tcp_send_head(sk); 2447 2448 BUG_ON(!skb || skb->len < mss_now); 2449 2450 tcp_write_xmit(sk, mss_now, TCP_NAGLE_PUSH, 1, sk->sk_allocation); 2451 } 2452 2453 /* This function returns the amount that we can raise the 2454 * usable window based on the following constraints 2455 * 2456 * 1. The window can never be shrunk once it is offered (RFC 793) 2457 * 2. We limit memory per socket 2458 * 2459 * RFC 1122: 2460 * "the suggested [SWS] avoidance algorithm for the receiver is to keep 2461 * RECV.NEXT + RCV.WIN fixed until: 2462 * RCV.BUFF - RCV.USER - RCV.WINDOW >= min(1/2 RCV.BUFF, MSS)" 2463 * 2464 * i.e. don't raise the right edge of the window until you can raise 2465 * it at least MSS bytes. 2466 * 2467 * Unfortunately, the recommended algorithm breaks header prediction, 2468 * since header prediction assumes th->window stays fixed. 2469 * 2470 * Strictly speaking, keeping th->window fixed violates the receiver 2471 * side SWS prevention criteria. The problem is that under this rule 2472 * a stream of single byte packets will cause the right side of the 2473 * window to always advance by a single byte. 2474 * 2475 * Of course, if the sender implements sender side SWS prevention 2476 * then this will not be a problem. 2477 * 2478 * BSD seems to make the following compromise: 2479 * 2480 * If the free space is less than the 1/4 of the maximum 2481 * space available and the free space is less than 1/2 mss, 2482 * then set the window to 0. 2483 * [ Actually, bsd uses MSS and 1/4 of maximal _window_ ] 2484 * Otherwise, just prevent the window from shrinking 2485 * and from being larger than the largest representable value. 2486 * 2487 * This prevents incremental opening of the window in the regime 2488 * where TCP is limited by the speed of the reader side taking 2489 * data out of the TCP receive queue. It does nothing about 2490 * those cases where the window is constrained on the sender side 2491 * because the pipeline is full. 2492 * 2493 * BSD also seems to "accidentally" limit itself to windows that are a 2494 * multiple of MSS, at least until the free space gets quite small. 2495 * This would appear to be a side effect of the mbuf implementation. 2496 * Combining these two algorithms results in the observed behavior 2497 * of having a fixed window size at almost all times. 2498 * 2499 * Below we obtain similar behavior by forcing the offered window to 2500 * a multiple of the mss when it is feasible to do so. 2501 * 2502 * Note, we don't "adjust" for TIMESTAMP or SACK option bytes. 2503 * Regular options like TIMESTAMP are taken into account. 2504 */ 2505 u32 __tcp_select_window(struct sock *sk) 2506 { 2507 struct inet_connection_sock *icsk = inet_csk(sk); 2508 struct tcp_sock *tp = tcp_sk(sk); 2509 /* MSS for the peer's data. Previous versions used mss_clamp 2510 * here. I don't know if the value based on our guesses 2511 * of peer's MSS is better for the performance. It's more correct 2512 * but may be worse for the performance because of rcv_mss 2513 * fluctuations. --SAW 1998/11/1 2514 */ 2515 int mss = icsk->icsk_ack.rcv_mss; 2516 int free_space = tcp_space(sk); 2517 int allowed_space = tcp_full_space(sk); 2518 int full_space = min_t(int, tp->window_clamp, allowed_space); 2519 int window; 2520 2521 if (mss > full_space) 2522 mss = full_space; 2523 2524 if (free_space < (full_space >> 1)) { 2525 icsk->icsk_ack.quick = 0; 2526 2527 if (tcp_under_memory_pressure(sk)) 2528 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 2529 4U * tp->advmss); 2530 2531 /* free_space might become our new window, make sure we don't 2532 * increase it due to wscale. 2533 */ 2534 free_space = round_down(free_space, 1 << tp->rx_opt.rcv_wscale); 2535 2536 /* if free space is less than mss estimate, or is below 1/16th 2537 * of the maximum allowed, try to move to zero-window, else 2538 * tcp_clamp_window() will grow rcv buf up to tcp_rmem[2], and 2539 * new incoming data is dropped due to memory limits. 2540 * With large window, mss test triggers way too late in order 2541 * to announce zero window in time before rmem limit kicks in. 2542 */ 2543 if (free_space < (allowed_space >> 4) || free_space < mss) 2544 return 0; 2545 } 2546 2547 if (free_space > tp->rcv_ssthresh) 2548 free_space = tp->rcv_ssthresh; 2549 2550 /* Don't do rounding if we are using window scaling, since the 2551 * scaled window will not line up with the MSS boundary anyway. 2552 */ 2553 window = tp->rcv_wnd; 2554 if (tp->rx_opt.rcv_wscale) { 2555 window = free_space; 2556 2557 /* Advertise enough space so that it won't get scaled away. 2558 * Import case: prevent zero window announcement if 2559 * 1<<rcv_wscale > mss. 2560 */ 2561 if (((window >> tp->rx_opt.rcv_wscale) << tp->rx_opt.rcv_wscale) != window) 2562 window = (((window >> tp->rx_opt.rcv_wscale) + 1) 2563 << tp->rx_opt.rcv_wscale); 2564 } else { 2565 /* Get the largest window that is a nice multiple of mss. 2566 * Window clamp already applied above. 2567 * If our current window offering is within 1 mss of the 2568 * free space we just keep it. This prevents the divide 2569 * and multiply from happening most of the time. 2570 * We also don't do any window rounding when the free space 2571 * is too small. 2572 */ 2573 if (window <= free_space - mss || window > free_space) 2574 window = (free_space / mss) * mss; 2575 else if (mss == full_space && 2576 free_space > window + (full_space >> 1)) 2577 window = free_space; 2578 } 2579 2580 return window; 2581 } 2582 2583 void tcp_skb_collapse_tstamp(struct sk_buff *skb, 2584 const struct sk_buff *next_skb) 2585 { 2586 if (unlikely(tcp_has_tx_tstamp(next_skb))) { 2587 const struct skb_shared_info *next_shinfo = 2588 skb_shinfo(next_skb); 2589 struct skb_shared_info *shinfo = skb_shinfo(skb); 2590 2591 shinfo->tx_flags |= next_shinfo->tx_flags & SKBTX_ANY_TSTAMP; 2592 shinfo->tskey = next_shinfo->tskey; 2593 TCP_SKB_CB(skb)->txstamp_ack |= 2594 TCP_SKB_CB(next_skb)->txstamp_ack; 2595 } 2596 } 2597 2598 /* Collapses two adjacent SKB's during retransmission. */ 2599 static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb) 2600 { 2601 struct tcp_sock *tp = tcp_sk(sk); 2602 struct sk_buff *next_skb = tcp_write_queue_next(sk, skb); 2603 int skb_size, next_skb_size; 2604 2605 skb_size = skb->len; 2606 next_skb_size = next_skb->len; 2607 2608 BUG_ON(tcp_skb_pcount(skb) != 1 || tcp_skb_pcount(next_skb) != 1); 2609 2610 if (next_skb_size) { 2611 if (next_skb_size <= skb_availroom(skb)) 2612 skb_copy_bits(next_skb, 0, skb_put(skb, next_skb_size), 2613 next_skb_size); 2614 else if (!skb_shift(skb, next_skb, next_skb_size)) 2615 return false; 2616 } 2617 tcp_highest_sack_combine(sk, next_skb, skb); 2618 2619 tcp_unlink_write_queue(next_skb, sk); 2620 2621 if (next_skb->ip_summed == CHECKSUM_PARTIAL) 2622 skb->ip_summed = CHECKSUM_PARTIAL; 2623 2624 if (skb->ip_summed != CHECKSUM_PARTIAL) 2625 skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size); 2626 2627 /* Update sequence range on original skb. */ 2628 TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq; 2629 2630 /* Merge over control information. This moves PSH/FIN etc. over */ 2631 TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(next_skb)->tcp_flags; 2632 2633 /* All done, get rid of second SKB and account for it so 2634 * packet counting does not break. 2635 */ 2636 TCP_SKB_CB(skb)->sacked |= TCP_SKB_CB(next_skb)->sacked & TCPCB_EVER_RETRANS; 2637 TCP_SKB_CB(skb)->eor = TCP_SKB_CB(next_skb)->eor; 2638 2639 /* changed transmit queue under us so clear hints */ 2640 tcp_clear_retrans_hints_partial(tp); 2641 if (next_skb == tp->retransmit_skb_hint) 2642 tp->retransmit_skb_hint = skb; 2643 2644 tcp_adjust_pcount(sk, next_skb, tcp_skb_pcount(next_skb)); 2645 2646 tcp_skb_collapse_tstamp(skb, next_skb); 2647 2648 sk_wmem_free_skb(sk, next_skb); 2649 return true; 2650 } 2651 2652 /* Check if coalescing SKBs is legal. */ 2653 static bool tcp_can_collapse(const struct sock *sk, const struct sk_buff *skb) 2654 { 2655 if (tcp_skb_pcount(skb) > 1) 2656 return false; 2657 if (skb_cloned(skb)) 2658 return false; 2659 if (skb == tcp_send_head(sk)) 2660 return false; 2661 /* Some heuristics for collapsing over SACK'd could be invented */ 2662 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) 2663 return false; 2664 2665 return true; 2666 } 2667 2668 /* Collapse packets in the retransmit queue to make to create 2669 * less packets on the wire. This is only done on retransmission. 2670 */ 2671 static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *to, 2672 int space) 2673 { 2674 struct tcp_sock *tp = tcp_sk(sk); 2675 struct sk_buff *skb = to, *tmp; 2676 bool first = true; 2677 2678 if (!sysctl_tcp_retrans_collapse) 2679 return; 2680 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 2681 return; 2682 2683 tcp_for_write_queue_from_safe(skb, tmp, sk) { 2684 if (!tcp_can_collapse(sk, skb)) 2685 break; 2686 2687 if (!tcp_skb_can_collapse_to(to)) 2688 break; 2689 2690 space -= skb->len; 2691 2692 if (first) { 2693 first = false; 2694 continue; 2695 } 2696 2697 if (space < 0) 2698 break; 2699 2700 if (after(TCP_SKB_CB(skb)->end_seq, tcp_wnd_end(tp))) 2701 break; 2702 2703 if (!tcp_collapse_retrans(sk, to)) 2704 break; 2705 } 2706 } 2707 2708 /* This retransmits one SKB. Policy decisions and retransmit queue 2709 * state updates are done by the caller. Returns non-zero if an 2710 * error occurred which prevented the send. 2711 */ 2712 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs) 2713 { 2714 struct inet_connection_sock *icsk = inet_csk(sk); 2715 struct tcp_sock *tp = tcp_sk(sk); 2716 unsigned int cur_mss; 2717 int diff, len, err; 2718 2719 2720 /* Inconclusive MTU probe */ 2721 if (icsk->icsk_mtup.probe_size) 2722 icsk->icsk_mtup.probe_size = 0; 2723 2724 /* Do not sent more than we queued. 1/4 is reserved for possible 2725 * copying overhead: fragmentation, tunneling, mangling etc. 2726 */ 2727 if (atomic_read(&sk->sk_wmem_alloc) > 2728 min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), 2729 sk->sk_sndbuf)) 2730 return -EAGAIN; 2731 2732 if (skb_still_in_host_queue(sk, skb)) 2733 return -EBUSY; 2734 2735 if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) { 2736 if (before(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) 2737 BUG(); 2738 if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) 2739 return -ENOMEM; 2740 } 2741 2742 if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk)) 2743 return -EHOSTUNREACH; /* Routing failure or similar. */ 2744 2745 cur_mss = tcp_current_mss(sk); 2746 2747 /* If receiver has shrunk his window, and skb is out of 2748 * new window, do not retransmit it. The exception is the 2749 * case, when window is shrunk to zero. In this case 2750 * our retransmit serves as a zero window probe. 2751 */ 2752 if (!before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp)) && 2753 TCP_SKB_CB(skb)->seq != tp->snd_una) 2754 return -EAGAIN; 2755 2756 len = cur_mss * segs; 2757 if (skb->len > len) { 2758 if (tcp_fragment(sk, skb, len, cur_mss, GFP_ATOMIC)) 2759 return -ENOMEM; /* We'll try again later. */ 2760 } else { 2761 if (skb_unclone(skb, GFP_ATOMIC)) 2762 return -ENOMEM; 2763 2764 diff = tcp_skb_pcount(skb); 2765 tcp_set_skb_tso_segs(skb, cur_mss); 2766 diff -= tcp_skb_pcount(skb); 2767 if (diff) 2768 tcp_adjust_pcount(sk, skb, diff); 2769 if (skb->len < cur_mss) 2770 tcp_retrans_try_collapse(sk, skb, cur_mss); 2771 } 2772 2773 /* RFC3168, section 6.1.1.1. ECN fallback */ 2774 if ((TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN_ECN) == TCPHDR_SYN_ECN) 2775 tcp_ecn_clear_syn(sk, skb); 2776 2777 /* make sure skb->data is aligned on arches that require it 2778 * and check if ack-trimming & collapsing extended the headroom 2779 * beyond what csum_start can cover. 2780 */ 2781 if (unlikely((NET_IP_ALIGN && ((unsigned long)skb->data & 3)) || 2782 skb_headroom(skb) >= 0xFFFF)) { 2783 struct sk_buff *nskb; 2784 2785 skb_mstamp_get(&skb->skb_mstamp); 2786 nskb = __pskb_copy(skb, MAX_TCP_HEADER, GFP_ATOMIC); 2787 err = nskb ? tcp_transmit_skb(sk, nskb, 0, GFP_ATOMIC) : 2788 -ENOBUFS; 2789 } else { 2790 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 2791 } 2792 2793 if (likely(!err)) { 2794 segs = tcp_skb_pcount(skb); 2795 2796 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS; 2797 /* Update global TCP statistics. */ 2798 TCP_ADD_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS, segs); 2799 if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN) 2800 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 2801 tp->total_retrans += segs; 2802 } 2803 return err; 2804 } 2805 2806 int tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs) 2807 { 2808 struct tcp_sock *tp = tcp_sk(sk); 2809 int err = __tcp_retransmit_skb(sk, skb, segs); 2810 2811 if (err == 0) { 2812 #if FASTRETRANS_DEBUG > 0 2813 if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { 2814 net_dbg_ratelimited("retrans_out leaked\n"); 2815 } 2816 #endif 2817 TCP_SKB_CB(skb)->sacked |= TCPCB_RETRANS; 2818 tp->retrans_out += tcp_skb_pcount(skb); 2819 2820 /* Save stamp of the first retransmit. */ 2821 if (!tp->retrans_stamp) 2822 tp->retrans_stamp = tcp_skb_timestamp(skb); 2823 2824 } else if (err != -EBUSY) { 2825 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL); 2826 } 2827 2828 if (tp->undo_retrans < 0) 2829 tp->undo_retrans = 0; 2830 tp->undo_retrans += tcp_skb_pcount(skb); 2831 return err; 2832 } 2833 2834 /* Check if we forward retransmits are possible in the current 2835 * window/congestion state. 2836 */ 2837 static bool tcp_can_forward_retransmit(struct sock *sk) 2838 { 2839 const struct inet_connection_sock *icsk = inet_csk(sk); 2840 const struct tcp_sock *tp = tcp_sk(sk); 2841 2842 /* Forward retransmissions are possible only during Recovery. */ 2843 if (icsk->icsk_ca_state != TCP_CA_Recovery) 2844 return false; 2845 2846 /* No forward retransmissions in Reno are possible. */ 2847 if (tcp_is_reno(tp)) 2848 return false; 2849 2850 /* Yeah, we have to make difficult choice between forward transmission 2851 * and retransmission... Both ways have their merits... 2852 * 2853 * For now we do not retransmit anything, while we have some new 2854 * segments to send. In the other cases, follow rule 3 for 2855 * NextSeg() specified in RFC3517. 2856 */ 2857 2858 if (tcp_may_send_now(sk)) 2859 return false; 2860 2861 return true; 2862 } 2863 2864 /* This gets called after a retransmit timeout, and the initially 2865 * retransmitted data is acknowledged. It tries to continue 2866 * resending the rest of the retransmit queue, until either 2867 * we've sent it all or the congestion window limit is reached. 2868 * If doing SACK, the first ACK which comes back for a timeout 2869 * based retransmit packet might feed us FACK information again. 2870 * If so, we use it to avoid unnecessarily retransmissions. 2871 */ 2872 void tcp_xmit_retransmit_queue(struct sock *sk) 2873 { 2874 const struct inet_connection_sock *icsk = inet_csk(sk); 2875 struct tcp_sock *tp = tcp_sk(sk); 2876 struct sk_buff *skb; 2877 struct sk_buff *hole = NULL; 2878 u32 max_segs, last_lost; 2879 int mib_idx; 2880 int fwd_rexmitting = 0; 2881 2882 if (!tp->packets_out) 2883 return; 2884 2885 if (!tp->lost_out) 2886 tp->retransmit_high = tp->snd_una; 2887 2888 if (tp->retransmit_skb_hint) { 2889 skb = tp->retransmit_skb_hint; 2890 last_lost = TCP_SKB_CB(skb)->end_seq; 2891 if (after(last_lost, tp->retransmit_high)) 2892 last_lost = tp->retransmit_high; 2893 } else { 2894 skb = tcp_write_queue_head(sk); 2895 last_lost = tp->snd_una; 2896 } 2897 2898 max_segs = tcp_tso_segs(sk, tcp_current_mss(sk)); 2899 tcp_for_write_queue_from(skb, sk) { 2900 __u8 sacked; 2901 int segs; 2902 2903 if (skb == tcp_send_head(sk)) 2904 break; 2905 /* we could do better than to assign each time */ 2906 if (!hole) 2907 tp->retransmit_skb_hint = skb; 2908 2909 segs = tp->snd_cwnd - tcp_packets_in_flight(tp); 2910 if (segs <= 0) 2911 return; 2912 sacked = TCP_SKB_CB(skb)->sacked; 2913 /* In case tcp_shift_skb_data() have aggregated large skbs, 2914 * we need to make sure not sending too bigs TSO packets 2915 */ 2916 segs = min_t(int, segs, max_segs); 2917 2918 if (fwd_rexmitting) { 2919 begin_fwd: 2920 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp))) 2921 break; 2922 mib_idx = LINUX_MIB_TCPFORWARDRETRANS; 2923 2924 } else if (!before(TCP_SKB_CB(skb)->seq, tp->retransmit_high)) { 2925 tp->retransmit_high = last_lost; 2926 if (!tcp_can_forward_retransmit(sk)) 2927 break; 2928 /* Backtrack if necessary to non-L'ed skb */ 2929 if (hole) { 2930 skb = hole; 2931 hole = NULL; 2932 } 2933 fwd_rexmitting = 1; 2934 goto begin_fwd; 2935 2936 } else if (!(sacked & TCPCB_LOST)) { 2937 if (!hole && !(sacked & (TCPCB_SACKED_RETRANS|TCPCB_SACKED_ACKED))) 2938 hole = skb; 2939 continue; 2940 2941 } else { 2942 last_lost = TCP_SKB_CB(skb)->end_seq; 2943 if (icsk->icsk_ca_state != TCP_CA_Loss) 2944 mib_idx = LINUX_MIB_TCPFASTRETRANS; 2945 else 2946 mib_idx = LINUX_MIB_TCPSLOWSTARTRETRANS; 2947 } 2948 2949 if (sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS)) 2950 continue; 2951 2952 if (tcp_small_queue_check(sk, skb, 1)) 2953 return; 2954 2955 if (tcp_retransmit_skb(sk, skb, segs)) 2956 return; 2957 2958 NET_ADD_STATS(sock_net(sk), mib_idx, tcp_skb_pcount(skb)); 2959 2960 if (tcp_in_cwnd_reduction(sk)) 2961 tp->prr_out += tcp_skb_pcount(skb); 2962 2963 if (skb == tcp_write_queue_head(sk)) 2964 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 2965 inet_csk(sk)->icsk_rto, 2966 TCP_RTO_MAX); 2967 } 2968 } 2969 2970 /* We allow to exceed memory limits for FIN packets to expedite 2971 * connection tear down and (memory) recovery. 2972 * Otherwise tcp_send_fin() could be tempted to either delay FIN 2973 * or even be forced to close flow without any FIN. 2974 * In general, we want to allow one skb per socket to avoid hangs 2975 * with edge trigger epoll() 2976 */ 2977 void sk_forced_mem_schedule(struct sock *sk, int size) 2978 { 2979 int amt; 2980 2981 if (size <= sk->sk_forward_alloc) 2982 return; 2983 amt = sk_mem_pages(size); 2984 sk->sk_forward_alloc += amt * SK_MEM_QUANTUM; 2985 sk_memory_allocated_add(sk, amt); 2986 2987 if (mem_cgroup_sockets_enabled && sk->sk_memcg) 2988 mem_cgroup_charge_skmem(sk->sk_memcg, amt); 2989 } 2990 2991 /* Send a FIN. The caller locks the socket for us. 2992 * We should try to send a FIN packet really hard, but eventually give up. 2993 */ 2994 void tcp_send_fin(struct sock *sk) 2995 { 2996 struct sk_buff *skb, *tskb = tcp_write_queue_tail(sk); 2997 struct tcp_sock *tp = tcp_sk(sk); 2998 2999 /* Optimization, tack on the FIN if we have one skb in write queue and 3000 * this skb was not yet sent, or we are under memory pressure. 3001 * Note: in the latter case, FIN packet will be sent after a timeout, 3002 * as TCP stack thinks it has already been transmitted. 3003 */ 3004 if (tskb && (tcp_send_head(sk) || tcp_under_memory_pressure(sk))) { 3005 coalesce: 3006 TCP_SKB_CB(tskb)->tcp_flags |= TCPHDR_FIN; 3007 TCP_SKB_CB(tskb)->end_seq++; 3008 tp->write_seq++; 3009 if (!tcp_send_head(sk)) { 3010 /* This means tskb was already sent. 3011 * Pretend we included the FIN on previous transmit. 3012 * We need to set tp->snd_nxt to the value it would have 3013 * if FIN had been sent. This is because retransmit path 3014 * does not change tp->snd_nxt. 3015 */ 3016 tp->snd_nxt++; 3017 return; 3018 } 3019 } else { 3020 skb = alloc_skb_fclone(MAX_TCP_HEADER, sk->sk_allocation); 3021 if (unlikely(!skb)) { 3022 if (tskb) 3023 goto coalesce; 3024 return; 3025 } 3026 skb_reserve(skb, MAX_TCP_HEADER); 3027 sk_forced_mem_schedule(sk, skb->truesize); 3028 /* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */ 3029 tcp_init_nondata_skb(skb, tp->write_seq, 3030 TCPHDR_ACK | TCPHDR_FIN); 3031 tcp_queue_skb(sk, skb); 3032 } 3033 __tcp_push_pending_frames(sk, tcp_current_mss(sk), TCP_NAGLE_OFF); 3034 } 3035 3036 /* We get here when a process closes a file descriptor (either due to 3037 * an explicit close() or as a byproduct of exit()'ing) and there 3038 * was unread data in the receive queue. This behavior is recommended 3039 * by RFC 2525, section 2.17. -DaveM 3040 */ 3041 void tcp_send_active_reset(struct sock *sk, gfp_t priority) 3042 { 3043 struct sk_buff *skb; 3044 3045 /* NOTE: No TCP options attached and we never retransmit this. */ 3046 skb = alloc_skb(MAX_TCP_HEADER, priority); 3047 if (!skb) { 3048 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 3049 return; 3050 } 3051 3052 /* Reserve space for headers and prepare control bits. */ 3053 skb_reserve(skb, MAX_TCP_HEADER); 3054 tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk), 3055 TCPHDR_ACK | TCPHDR_RST); 3056 skb_mstamp_get(&skb->skb_mstamp); 3057 /* Send it off. */ 3058 if (tcp_transmit_skb(sk, skb, 0, priority)) 3059 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED); 3060 3061 TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTRSTS); 3062 } 3063 3064 /* Send a crossed SYN-ACK during socket establishment. 3065 * WARNING: This routine must only be called when we have already sent 3066 * a SYN packet that crossed the incoming SYN that caused this routine 3067 * to get called. If this assumption fails then the initial rcv_wnd 3068 * and rcv_wscale values will not be correct. 3069 */ 3070 int tcp_send_synack(struct sock *sk) 3071 { 3072 struct sk_buff *skb; 3073 3074 skb = tcp_write_queue_head(sk); 3075 if (!skb || !(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) { 3076 pr_debug("%s: wrong queue state\n", __func__); 3077 return -EFAULT; 3078 } 3079 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)) { 3080 if (skb_cloned(skb)) { 3081 struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC); 3082 if (!nskb) 3083 return -ENOMEM; 3084 tcp_unlink_write_queue(skb, sk); 3085 __skb_header_release(nskb); 3086 __tcp_add_write_queue_head(sk, nskb); 3087 sk_wmem_free_skb(sk, skb); 3088 sk->sk_wmem_queued += nskb->truesize; 3089 sk_mem_charge(sk, nskb->truesize); 3090 skb = nskb; 3091 } 3092 3093 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_ACK; 3094 tcp_ecn_send_synack(sk, skb); 3095 } 3096 return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 3097 } 3098 3099 /** 3100 * tcp_make_synack - Prepare a SYN-ACK. 3101 * sk: listener socket 3102 * dst: dst entry attached to the SYNACK 3103 * req: request_sock pointer 3104 * 3105 * Allocate one skb and build a SYNACK packet. 3106 * @dst is consumed : Caller should not use it again. 3107 */ 3108 struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst, 3109 struct request_sock *req, 3110 struct tcp_fastopen_cookie *foc, 3111 enum tcp_synack_type synack_type) 3112 { 3113 struct inet_request_sock *ireq = inet_rsk(req); 3114 const struct tcp_sock *tp = tcp_sk(sk); 3115 struct tcp_md5sig_key *md5 = NULL; 3116 struct tcp_out_options opts; 3117 struct sk_buff *skb; 3118 int tcp_header_size; 3119 struct tcphdr *th; 3120 u16 user_mss; 3121 int mss; 3122 3123 skb = alloc_skb(MAX_TCP_HEADER, GFP_ATOMIC); 3124 if (unlikely(!skb)) { 3125 dst_release(dst); 3126 return NULL; 3127 } 3128 /* Reserve space for headers. */ 3129 skb_reserve(skb, MAX_TCP_HEADER); 3130 3131 switch (synack_type) { 3132 case TCP_SYNACK_NORMAL: 3133 skb_set_owner_w(skb, req_to_sk(req)); 3134 break; 3135 case TCP_SYNACK_COOKIE: 3136 /* Under synflood, we do not attach skb to a socket, 3137 * to avoid false sharing. 3138 */ 3139 break; 3140 case TCP_SYNACK_FASTOPEN: 3141 /* sk is a const pointer, because we want to express multiple 3142 * cpu might call us concurrently. 3143 * sk->sk_wmem_alloc in an atomic, we can promote to rw. 3144 */ 3145 skb_set_owner_w(skb, (struct sock *)sk); 3146 break; 3147 } 3148 skb_dst_set(skb, dst); 3149 3150 mss = dst_metric_advmss(dst); 3151 user_mss = READ_ONCE(tp->rx_opt.user_mss); 3152 if (user_mss && user_mss < mss) 3153 mss = user_mss; 3154 3155 memset(&opts, 0, sizeof(opts)); 3156 #ifdef CONFIG_SYN_COOKIES 3157 if (unlikely(req->cookie_ts)) 3158 skb->skb_mstamp.stamp_jiffies = cookie_init_timestamp(req); 3159 else 3160 #endif 3161 skb_mstamp_get(&skb->skb_mstamp); 3162 3163 #ifdef CONFIG_TCP_MD5SIG 3164 rcu_read_lock(); 3165 md5 = tcp_rsk(req)->af_specific->req_md5_lookup(sk, req_to_sk(req)); 3166 #endif 3167 skb_set_hash(skb, tcp_rsk(req)->txhash, PKT_HASH_TYPE_L4); 3168 tcp_header_size = tcp_synack_options(req, mss, skb, &opts, md5, foc) + 3169 sizeof(*th); 3170 3171 skb_push(skb, tcp_header_size); 3172 skb_reset_transport_header(skb); 3173 3174 th = (struct tcphdr *)skb->data; 3175 memset(th, 0, sizeof(struct tcphdr)); 3176 th->syn = 1; 3177 th->ack = 1; 3178 tcp_ecn_make_synack(req, th); 3179 th->source = htons(ireq->ir_num); 3180 th->dest = ireq->ir_rmt_port; 3181 /* Setting of flags are superfluous here for callers (and ECE is 3182 * not even correctly set) 3183 */ 3184 tcp_init_nondata_skb(skb, tcp_rsk(req)->snt_isn, 3185 TCPHDR_SYN | TCPHDR_ACK); 3186 3187 th->seq = htonl(TCP_SKB_CB(skb)->seq); 3188 /* XXX data is queued and acked as is. No buffer/window check */ 3189 th->ack_seq = htonl(tcp_rsk(req)->rcv_nxt); 3190 3191 /* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */ 3192 th->window = htons(min(req->rsk_rcv_wnd, 65535U)); 3193 tcp_options_write((__be32 *)(th + 1), NULL, &opts); 3194 th->doff = (tcp_header_size >> 2); 3195 __TCP_INC_STATS(sock_net(sk), TCP_MIB_OUTSEGS); 3196 3197 #ifdef CONFIG_TCP_MD5SIG 3198 /* Okay, we have all we need - do the md5 hash if needed */ 3199 if (md5) 3200 tcp_rsk(req)->af_specific->calc_md5_hash(opts.hash_location, 3201 md5, req_to_sk(req), skb); 3202 rcu_read_unlock(); 3203 #endif 3204 3205 /* Do not fool tcpdump (if any), clean our debris */ 3206 skb->tstamp = 0; 3207 return skb; 3208 } 3209 EXPORT_SYMBOL(tcp_make_synack); 3210 3211 static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst) 3212 { 3213 struct inet_connection_sock *icsk = inet_csk(sk); 3214 const struct tcp_congestion_ops *ca; 3215 u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); 3216 3217 if (ca_key == TCP_CA_UNSPEC) 3218 return; 3219 3220 rcu_read_lock(); 3221 ca = tcp_ca_find_key(ca_key); 3222 if (likely(ca && try_module_get(ca->owner))) { 3223 module_put(icsk->icsk_ca_ops->owner); 3224 icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); 3225 icsk->icsk_ca_ops = ca; 3226 } 3227 rcu_read_unlock(); 3228 } 3229 3230 /* Do all connect socket setups that can be done AF independent. */ 3231 static void tcp_connect_init(struct sock *sk) 3232 { 3233 const struct dst_entry *dst = __sk_dst_get(sk); 3234 struct tcp_sock *tp = tcp_sk(sk); 3235 __u8 rcv_wscale; 3236 3237 /* We'll fix this up when we get a response from the other end. 3238 * See tcp_input.c:tcp_rcv_state_process case TCP_SYN_SENT. 3239 */ 3240 tp->tcp_header_len = sizeof(struct tcphdr) + 3241 (sysctl_tcp_timestamps ? TCPOLEN_TSTAMP_ALIGNED : 0); 3242 3243 #ifdef CONFIG_TCP_MD5SIG 3244 if (tp->af_specific->md5_lookup(sk, sk)) 3245 tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; 3246 #endif 3247 3248 /* If user gave his TCP_MAXSEG, record it to clamp */ 3249 if (tp->rx_opt.user_mss) 3250 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 3251 tp->max_window = 0; 3252 tcp_mtup_init(sk); 3253 tcp_sync_mss(sk, dst_mtu(dst)); 3254 3255 tcp_ca_dst_init(sk, dst); 3256 3257 if (!tp->window_clamp) 3258 tp->window_clamp = dst_metric(dst, RTAX_WINDOW); 3259 tp->advmss = dst_metric_advmss(dst); 3260 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->advmss) 3261 tp->advmss = tp->rx_opt.user_mss; 3262 3263 tcp_initialize_rcv_mss(sk); 3264 3265 /* limit the window selection if the user enforce a smaller rx buffer */ 3266 if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && 3267 (tp->window_clamp > tcp_full_space(sk) || tp->window_clamp == 0)) 3268 tp->window_clamp = tcp_full_space(sk); 3269 3270 tcp_select_initial_window(tcp_full_space(sk), 3271 tp->advmss - (tp->rx_opt.ts_recent_stamp ? tp->tcp_header_len - sizeof(struct tcphdr) : 0), 3272 &tp->rcv_wnd, 3273 &tp->window_clamp, 3274 sysctl_tcp_window_scaling, 3275 &rcv_wscale, 3276 dst_metric(dst, RTAX_INITRWND)); 3277 3278 tp->rx_opt.rcv_wscale = rcv_wscale; 3279 tp->rcv_ssthresh = tp->rcv_wnd; 3280 3281 sk->sk_err = 0; 3282 sock_reset_flag(sk, SOCK_DONE); 3283 tp->snd_wnd = 0; 3284 tcp_init_wl(tp, 0); 3285 tp->snd_una = tp->write_seq; 3286 tp->snd_sml = tp->write_seq; 3287 tp->snd_up = tp->write_seq; 3288 tp->snd_nxt = tp->write_seq; 3289 3290 if (likely(!tp->repair)) 3291 tp->rcv_nxt = 0; 3292 else 3293 tp->rcv_tstamp = tcp_time_stamp; 3294 tp->rcv_wup = tp->rcv_nxt; 3295 tp->copied_seq = tp->rcv_nxt; 3296 3297 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; 3298 inet_csk(sk)->icsk_retransmits = 0; 3299 tcp_clear_retrans(tp); 3300 } 3301 3302 static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb) 3303 { 3304 struct tcp_sock *tp = tcp_sk(sk); 3305 struct tcp_skb_cb *tcb = TCP_SKB_CB(skb); 3306 3307 tcb->end_seq += skb->len; 3308 __skb_header_release(skb); 3309 __tcp_add_write_queue_tail(sk, skb); 3310 sk->sk_wmem_queued += skb->truesize; 3311 sk_mem_charge(sk, skb->truesize); 3312 tp->write_seq = tcb->end_seq; 3313 tp->packets_out += tcp_skb_pcount(skb); 3314 } 3315 3316 /* Build and send a SYN with data and (cached) Fast Open cookie. However, 3317 * queue a data-only packet after the regular SYN, such that regular SYNs 3318 * are retransmitted on timeouts. Also if the remote SYN-ACK acknowledges 3319 * only the SYN sequence, the data are retransmitted in the first ACK. 3320 * If cookie is not cached or other error occurs, falls back to send a 3321 * regular SYN with Fast Open cookie request option. 3322 */ 3323 static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn) 3324 { 3325 struct tcp_sock *tp = tcp_sk(sk); 3326 struct tcp_fastopen_request *fo = tp->fastopen_req; 3327 int syn_loss = 0, space, err = 0; 3328 unsigned long last_syn_loss = 0; 3329 struct sk_buff *syn_data; 3330 3331 tp->rx_opt.mss_clamp = tp->advmss; /* If MSS is not cached */ 3332 tcp_fastopen_cache_get(sk, &tp->rx_opt.mss_clamp, &fo->cookie, 3333 &syn_loss, &last_syn_loss); 3334 /* Recurring FO SYN losses: revert to regular handshake temporarily */ 3335 if (syn_loss > 1 && 3336 time_before(jiffies, last_syn_loss + (60*HZ << syn_loss))) { 3337 fo->cookie.len = -1; 3338 goto fallback; 3339 } 3340 3341 if (sysctl_tcp_fastopen & TFO_CLIENT_NO_COOKIE) 3342 fo->cookie.len = -1; 3343 else if (fo->cookie.len <= 0) 3344 goto fallback; 3345 3346 /* MSS for SYN-data is based on cached MSS and bounded by PMTU and 3347 * user-MSS. Reserve maximum option space for middleboxes that add 3348 * private TCP options. The cost is reduced data space in SYN :( 3349 */ 3350 if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < tp->rx_opt.mss_clamp) 3351 tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; 3352 space = __tcp_mtu_to_mss(sk, inet_csk(sk)->icsk_pmtu_cookie) - 3353 MAX_TCP_OPTION_SPACE; 3354 3355 space = min_t(size_t, space, fo->size); 3356 3357 /* limit to order-0 allocations */ 3358 space = min_t(size_t, space, SKB_MAX_HEAD(MAX_TCP_HEADER)); 3359 3360 syn_data = sk_stream_alloc_skb(sk, space, sk->sk_allocation, false); 3361 if (!syn_data) 3362 goto fallback; 3363 syn_data->ip_summed = CHECKSUM_PARTIAL; 3364 memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)); 3365 if (space) { 3366 int copied = copy_from_iter(skb_put(syn_data, space), space, 3367 &fo->data->msg_iter); 3368 if (unlikely(!copied)) { 3369 kfree_skb(syn_data); 3370 goto fallback; 3371 } 3372 if (copied != space) { 3373 skb_trim(syn_data, copied); 3374 space = copied; 3375 } 3376 } 3377 /* No more data pending in inet_wait_for_connect() */ 3378 if (space == fo->size) 3379 fo->data = NULL; 3380 fo->copied = space; 3381 3382 tcp_connect_queue_skb(sk, syn_data); 3383 if (syn_data->len) 3384 tcp_chrono_start(sk, TCP_CHRONO_BUSY); 3385 3386 err = tcp_transmit_skb(sk, syn_data, 1, sk->sk_allocation); 3387 3388 syn->skb_mstamp = syn_data->skb_mstamp; 3389 3390 /* Now full SYN+DATA was cloned and sent (or not), 3391 * remove the SYN from the original skb (syn_data) 3392 * we keep in write queue in case of a retransmit, as we 3393 * also have the SYN packet (with no data) in the same queue. 3394 */ 3395 TCP_SKB_CB(syn_data)->seq++; 3396 TCP_SKB_CB(syn_data)->tcp_flags = TCPHDR_ACK | TCPHDR_PSH; 3397 if (!err) { 3398 tp->syn_data = (fo->copied > 0); 3399 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT); 3400 goto done; 3401 } 3402 3403 fallback: 3404 /* Send a regular SYN with Fast Open cookie request option */ 3405 if (fo->cookie.len > 0) 3406 fo->cookie.len = 0; 3407 err = tcp_transmit_skb(sk, syn, 1, sk->sk_allocation); 3408 if (err) 3409 tp->syn_fastopen = 0; 3410 done: 3411 fo->cookie.len = -1; /* Exclude Fast Open option for SYN retries */ 3412 return err; 3413 } 3414 3415 /* Build a SYN and send it off. */ 3416 int tcp_connect(struct sock *sk) 3417 { 3418 struct tcp_sock *tp = tcp_sk(sk); 3419 struct sk_buff *buff; 3420 int err; 3421 3422 tcp_connect_init(sk); 3423 3424 if (unlikely(tp->repair)) { 3425 tcp_finish_connect(sk, NULL); 3426 return 0; 3427 } 3428 3429 buff = sk_stream_alloc_skb(sk, 0, sk->sk_allocation, true); 3430 if (unlikely(!buff)) 3431 return -ENOBUFS; 3432 3433 tcp_init_nondata_skb(buff, tp->write_seq++, TCPHDR_SYN); 3434 tp->retrans_stamp = tcp_time_stamp; 3435 tcp_connect_queue_skb(sk, buff); 3436 tcp_ecn_send_syn(sk, buff); 3437 3438 /* Send off SYN; include data in Fast Open. */ 3439 err = tp->fastopen_req ? tcp_send_syn_data(sk, buff) : 3440 tcp_transmit_skb(sk, buff, 1, sk->sk_allocation); 3441 if (err == -ECONNREFUSED) 3442 return err; 3443 3444 /* We change tp->snd_nxt after the tcp_transmit_skb() call 3445 * in order to make this packet get counted in tcpOutSegs. 3446 */ 3447 tp->snd_nxt = tp->write_seq; 3448 tp->pushed_seq = tp->write_seq; 3449 TCP_INC_STATS(sock_net(sk), TCP_MIB_ACTIVEOPENS); 3450 3451 /* Timer for repeating the SYN until an answer. */ 3452 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 3453 inet_csk(sk)->icsk_rto, TCP_RTO_MAX); 3454 return 0; 3455 } 3456 EXPORT_SYMBOL(tcp_connect); 3457 3458 /* Send out a delayed ack, the caller does the policy checking 3459 * to see if we should even be here. See tcp_input.c:tcp_ack_snd_check() 3460 * for details. 3461 */ 3462 void tcp_send_delayed_ack(struct sock *sk) 3463 { 3464 struct inet_connection_sock *icsk = inet_csk(sk); 3465 int ato = icsk->icsk_ack.ato; 3466 unsigned long timeout; 3467 3468 tcp_ca_event(sk, CA_EVENT_DELAYED_ACK); 3469 3470 if (ato > TCP_DELACK_MIN) { 3471 const struct tcp_sock *tp = tcp_sk(sk); 3472 int max_ato = HZ / 2; 3473 3474 if (icsk->icsk_ack.pingpong || 3475 (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)) 3476 max_ato = TCP_DELACK_MAX; 3477 3478 /* Slow path, intersegment interval is "high". */ 3479 3480 /* If some rtt estimate is known, use it to bound delayed ack. 3481 * Do not use inet_csk(sk)->icsk_rto here, use results of rtt measurements 3482 * directly. 3483 */ 3484 if (tp->srtt_us) { 3485 int rtt = max_t(int, usecs_to_jiffies(tp->srtt_us >> 3), 3486 TCP_DELACK_MIN); 3487 3488 if (rtt < max_ato) 3489 max_ato = rtt; 3490 } 3491 3492 ato = min(ato, max_ato); 3493 } 3494 3495 /* Stay within the limit we were given */ 3496 timeout = jiffies + ato; 3497 3498 /* Use new timeout only if there wasn't a older one earlier. */ 3499 if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) { 3500 /* If delack timer was blocked or is about to expire, 3501 * send ACK now. 3502 */ 3503 if (icsk->icsk_ack.blocked || 3504 time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) { 3505 tcp_send_ack(sk); 3506 return; 3507 } 3508 3509 if (!time_before(timeout, icsk->icsk_ack.timeout)) 3510 timeout = icsk->icsk_ack.timeout; 3511 } 3512 icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; 3513 icsk->icsk_ack.timeout = timeout; 3514 sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); 3515 } 3516 3517 /* This routine sends an ack and also updates the window. */ 3518 void tcp_send_ack(struct sock *sk) 3519 { 3520 struct sk_buff *buff; 3521 3522 /* If we have been reset, we may not send again. */ 3523 if (sk->sk_state == TCP_CLOSE) 3524 return; 3525 3526 tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK); 3527 3528 /* We are not putting this on the write queue, so 3529 * tcp_transmit_skb() will set the ownership to this 3530 * sock. 3531 */ 3532 buff = alloc_skb(MAX_TCP_HEADER, 3533 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN)); 3534 if (unlikely(!buff)) { 3535 inet_csk_schedule_ack(sk); 3536 inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN; 3537 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, 3538 TCP_DELACK_MAX, TCP_RTO_MAX); 3539 return; 3540 } 3541 3542 /* Reserve space for headers and prepare control bits. */ 3543 skb_reserve(buff, MAX_TCP_HEADER); 3544 tcp_init_nondata_skb(buff, tcp_acceptable_seq(sk), TCPHDR_ACK); 3545 3546 /* We do not want pure acks influencing TCP Small Queues or fq/pacing 3547 * too much. 3548 * SKB_TRUESIZE(max(1 .. 66, MAX_TCP_HEADER)) is unfortunately ~784 3549 */ 3550 skb_set_tcp_pure_ack(buff); 3551 3552 /* Send it off, this clears delayed acks for us. */ 3553 skb_mstamp_get(&buff->skb_mstamp); 3554 tcp_transmit_skb(sk, buff, 0, (__force gfp_t)0); 3555 } 3556 EXPORT_SYMBOL_GPL(tcp_send_ack); 3557 3558 /* This routine sends a packet with an out of date sequence 3559 * number. It assumes the other end will try to ack it. 3560 * 3561 * Question: what should we make while urgent mode? 3562 * 4.4BSD forces sending single byte of data. We cannot send 3563 * out of window data, because we have SND.NXT==SND.MAX... 3564 * 3565 * Current solution: to send TWO zero-length segments in urgent mode: 3566 * one is with SEG.SEQ=SND.UNA to deliver urgent pointer, another is 3567 * out-of-date with SND.UNA-1 to probe window. 3568 */ 3569 static int tcp_xmit_probe_skb(struct sock *sk, int urgent, int mib) 3570 { 3571 struct tcp_sock *tp = tcp_sk(sk); 3572 struct sk_buff *skb; 3573 3574 /* We don't queue it, tcp_transmit_skb() sets ownership. */ 3575 skb = alloc_skb(MAX_TCP_HEADER, 3576 sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN)); 3577 if (!skb) 3578 return -1; 3579 3580 /* Reserve space for headers and set control bits. */ 3581 skb_reserve(skb, MAX_TCP_HEADER); 3582 /* Use a previous sequence. This should cause the other 3583 * end to send an ack. Don't queue or clone SKB, just 3584 * send it. 3585 */ 3586 tcp_init_nondata_skb(skb, tp->snd_una - !urgent, TCPHDR_ACK); 3587 skb_mstamp_get(&skb->skb_mstamp); 3588 NET_INC_STATS(sock_net(sk), mib); 3589 return tcp_transmit_skb(sk, skb, 0, (__force gfp_t)0); 3590 } 3591 3592 void tcp_send_window_probe(struct sock *sk) 3593 { 3594 if (sk->sk_state == TCP_ESTABLISHED) { 3595 tcp_sk(sk)->snd_wl1 = tcp_sk(sk)->rcv_nxt - 1; 3596 tcp_xmit_probe_skb(sk, 0, LINUX_MIB_TCPWINPROBE); 3597 } 3598 } 3599 3600 /* Initiate keepalive or window probe from timer. */ 3601 int tcp_write_wakeup(struct sock *sk, int mib) 3602 { 3603 struct tcp_sock *tp = tcp_sk(sk); 3604 struct sk_buff *skb; 3605 3606 if (sk->sk_state == TCP_CLOSE) 3607 return -1; 3608 3609 skb = tcp_send_head(sk); 3610 if (skb && before(TCP_SKB_CB(skb)->seq, tcp_wnd_end(tp))) { 3611 int err; 3612 unsigned int mss = tcp_current_mss(sk); 3613 unsigned int seg_size = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq; 3614 3615 if (before(tp->pushed_seq, TCP_SKB_CB(skb)->end_seq)) 3616 tp->pushed_seq = TCP_SKB_CB(skb)->end_seq; 3617 3618 /* We are probing the opening of a window 3619 * but the window size is != 0 3620 * must have been a result SWS avoidance ( sender ) 3621 */ 3622 if (seg_size < TCP_SKB_CB(skb)->end_seq - TCP_SKB_CB(skb)->seq || 3623 skb->len > mss) { 3624 seg_size = min(seg_size, mss); 3625 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 3626 if (tcp_fragment(sk, skb, seg_size, mss, GFP_ATOMIC)) 3627 return -1; 3628 } else if (!tcp_skb_pcount(skb)) 3629 tcp_set_skb_tso_segs(skb, mss); 3630 3631 TCP_SKB_CB(skb)->tcp_flags |= TCPHDR_PSH; 3632 err = tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC); 3633 if (!err) 3634 tcp_event_new_data_sent(sk, skb); 3635 return err; 3636 } else { 3637 if (between(tp->snd_up, tp->snd_una + 1, tp->snd_una + 0xFFFF)) 3638 tcp_xmit_probe_skb(sk, 1, mib); 3639 return tcp_xmit_probe_skb(sk, 0, mib); 3640 } 3641 } 3642 3643 /* A window probe timeout has occurred. If window is not closed send 3644 * a partial packet else a zero probe. 3645 */ 3646 void tcp_send_probe0(struct sock *sk) 3647 { 3648 struct inet_connection_sock *icsk = inet_csk(sk); 3649 struct tcp_sock *tp = tcp_sk(sk); 3650 struct net *net = sock_net(sk); 3651 unsigned long probe_max; 3652 int err; 3653 3654 err = tcp_write_wakeup(sk, LINUX_MIB_TCPWINPROBE); 3655 3656 if (tp->packets_out || !tcp_send_head(sk)) { 3657 /* Cancel probe timer, if it is not required. */ 3658 icsk->icsk_probes_out = 0; 3659 icsk->icsk_backoff = 0; 3660 return; 3661 } 3662 3663 if (err <= 0) { 3664 if (icsk->icsk_backoff < net->ipv4.sysctl_tcp_retries2) 3665 icsk->icsk_backoff++; 3666 icsk->icsk_probes_out++; 3667 probe_max = TCP_RTO_MAX; 3668 } else { 3669 /* If packet was not sent due to local congestion, 3670 * do not backoff and do not remember icsk_probes_out. 3671 * Let local senders to fight for local resources. 3672 * 3673 * Use accumulated backoff yet. 3674 */ 3675 if (!icsk->icsk_probes_out) 3676 icsk->icsk_probes_out = 1; 3677 probe_max = TCP_RESOURCE_PROBE_INTERVAL; 3678 } 3679 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0, 3680 tcp_probe0_when(sk, probe_max), 3681 TCP_RTO_MAX); 3682 } 3683 3684 int tcp_rtx_synack(const struct sock *sk, struct request_sock *req) 3685 { 3686 const struct tcp_request_sock_ops *af_ops = tcp_rsk(req)->af_specific; 3687 struct flowi fl; 3688 int res; 3689 3690 tcp_rsk(req)->txhash = net_tx_rndhash(); 3691 res = af_ops->send_synack(sk, NULL, &fl, req, NULL, TCP_SYNACK_NORMAL); 3692 if (!res) { 3693 __TCP_INC_STATS(sock_net(sk), TCP_MIB_RETRANSSEGS); 3694 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNRETRANS); 3695 if (unlikely(tcp_passive_fastopen(sk))) 3696 tcp_sk(sk)->total_retrans++; 3697 } 3698 return res; 3699 } 3700 EXPORT_SYMBOL(tcp_rtx_synack); 3701