linux/net/ipv4/tcp_timer.c
<<
>>
Prefs
   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4 *              operating system.  INET is implemented using the  BSD Socket
   5 *              interface as the means of communication with the user level.
   6 *
   7 *              Implementation of the Transmission Control Protocol(TCP).
   8 *
   9 * Authors:     Ross Biro
  10 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  11 *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  12 *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  13 *              Florian La Roche, <flla@stud.uni-sb.de>
  14 *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  15 *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  16 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  17 *              Matthew Dillon, <dillon@apollo.west.oic.com>
  18 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  19 *              Jorge Cwik, <jorge@laser.satlink.net>
  20 */
  21
  22#include <linux/module.h>
  23#include <linux/gfp.h>
  24#include <net/tcp.h>
  25
  26static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
  27{
  28        struct inet_connection_sock *icsk = inet_csk(sk);
  29        u32 elapsed, start_ts;
  30        s32 remaining;
  31
  32        start_ts = tcp_sk(sk)->retrans_stamp;
  33        if (!icsk->icsk_user_timeout)
  34                return icsk->icsk_rto;
  35        elapsed = tcp_time_stamp(tcp_sk(sk)) - start_ts;
  36        remaining = icsk->icsk_user_timeout - elapsed;
  37        if (remaining <= 0)
  38                return 1; /* user timeout has passed; fire ASAP */
  39
  40        return min_t(u32, icsk->icsk_rto, msecs_to_jiffies(remaining));
  41}
  42
  43u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
  44{
  45        struct inet_connection_sock *icsk = inet_csk(sk);
  46        u32 remaining;
  47        s32 elapsed;
  48
  49        if (!icsk->icsk_user_timeout || !icsk->icsk_probes_tstamp)
  50                return when;
  51
  52        elapsed = tcp_jiffies32 - icsk->icsk_probes_tstamp;
  53        if (unlikely(elapsed < 0))
  54                elapsed = 0;
  55        remaining = msecs_to_jiffies(icsk->icsk_user_timeout) - elapsed;
  56        remaining = max_t(u32, remaining, TCP_TIMEOUT_MIN);
  57
  58        return min_t(u32, remaining, when);
  59}
  60
  61/**
  62 *  tcp_write_err() - close socket and save error info
  63 *  @sk:  The socket the error has appeared on.
  64 *
  65 *  Returns: Nothing (void)
  66 */
  67
  68static void tcp_write_err(struct sock *sk)
  69{
  70        sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  71        sk_error_report(sk);
  72
  73        tcp_write_queue_purge(sk);
  74        tcp_done(sk);
  75        __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  76}
  77
  78/**
  79 *  tcp_out_of_resources() - Close socket if out of resources
  80 *  @sk:        pointer to current socket
  81 *  @do_reset:  send a last packet with reset flag
  82 *
  83 *  Do not allow orphaned sockets to eat all our resources.
  84 *  This is direct violation of TCP specs, but it is required
  85 *  to prevent DoS attacks. It is called when a retransmission timeout
  86 *  or zero probe timeout occurs on orphaned socket.
  87 *
  88 *  Also close if our net namespace is exiting; in that case there is no
  89 *  hope of ever communicating again since all netns interfaces are already
  90 *  down (or about to be down), and we need to release our dst references,
  91 *  which have been moved to the netns loopback interface, so the namespace
  92 *  can finish exiting.  This condition is only possible if we are a kernel
  93 *  socket, as those do not hold references to the namespace.
  94 *
  95 *  Criteria is still not confirmed experimentally and may change.
  96 *  We kill the socket, if:
  97 *  1. If number of orphaned sockets exceeds an administratively configured
  98 *     limit.
  99 *  2. If we have strong memory pressure.
 100 *  3. If our net namespace is exiting.
 101 */
 102static int tcp_out_of_resources(struct sock *sk, bool do_reset)
 103{
 104        struct tcp_sock *tp = tcp_sk(sk);
 105        int shift = 0;
 106
 107        /* If peer does not open window for long time, or did not transmit
 108         * anything for long time, penalize it. */
 109        if ((s32)(tcp_jiffies32 - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
 110                shift++;
 111
 112        /* If some dubious ICMP arrived, penalize even more. */
 113        if (sk->sk_err_soft)
 114                shift++;
 115
 116        if (tcp_check_oom(sk, shift)) {
 117                /* Catch exceptional cases, when connection requires reset.
 118                 *      1. Last segment was sent recently. */
 119                if ((s32)(tcp_jiffies32 - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
 120                    /*  2. Window is closed. */
 121                    (!tp->snd_wnd && !tp->packets_out))
 122                        do_reset = true;
 123                if (do_reset)
 124                        tcp_send_active_reset(sk, GFP_ATOMIC);
 125                tcp_done(sk);
 126                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
 127                return 1;
 128        }
 129
 130        if (!check_net(sock_net(sk))) {
 131                /* Not possible to send reset; just close */
 132                tcp_done(sk);
 133                return 1;
 134        }
 135
 136        return 0;
 137}
 138
 139/**
 140 *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
 141 *  @sk:    Pointer to the current socket.
 142 *  @alive: bool, socket alive state
 143 */
 144static int tcp_orphan_retries(struct sock *sk, bool alive)
 145{
 146        int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */
 147
 148        /* We know from an ICMP that something is wrong. */
 149        if (sk->sk_err_soft && !alive)
 150                retries = 0;
 151
 152        /* However, if socket sent something recently, select some safe
 153         * number of retries. 8 corresponds to >100 seconds with minimal
 154         * RTO of 200msec. */
 155        if (retries == 0 && alive)
 156                retries = 8;
 157        return retries;
 158}
 159
 160static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 161{
 162        const struct net *net = sock_net(sk);
 163        int mss;
 164
 165        /* Black hole detection */
 166        if (!net->ipv4.sysctl_tcp_mtu_probing)
 167                return;
 168
 169        if (!icsk->icsk_mtup.enabled) {
 170                icsk->icsk_mtup.enabled = 1;
 171                icsk->icsk_mtup.probe_timestamp = tcp_jiffies32;
 172        } else {
 173                mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 174                mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
 175                mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
 176                mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
 177                icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 178        }
 179        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 180}
 181
 182static unsigned int tcp_model_timeout(struct sock *sk,
 183                                      unsigned int boundary,
 184                                      unsigned int rto_base)
 185{
 186        unsigned int linear_backoff_thresh, timeout;
 187
 188        linear_backoff_thresh = ilog2(TCP_RTO_MAX / rto_base);
 189        if (boundary <= linear_backoff_thresh)
 190                timeout = ((2 << boundary) - 1) * rto_base;
 191        else
 192                timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 193                        (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 194        return jiffies_to_msecs(timeout);
 195}
 196/**
 197 *  retransmits_timed_out() - returns true if this connection has timed out
 198 *  @sk:       The current socket
 199 *  @boundary: max number of retransmissions
 200 *  @timeout:  A custom timeout value.
 201 *             If set to 0 the default timeout is calculated and used.
 202 *             Using TCP_RTO_MIN and the number of unsuccessful retransmits.
 203 *
 204 * The default "timeout" value this function can calculate and use
 205 * is equivalent to the timeout of a TCP Connection
 206 * after "boundary" unsuccessful, exponentially backed-off
 207 * retransmissions with an initial RTO of TCP_RTO_MIN.
 208 */
 209static bool retransmits_timed_out(struct sock *sk,
 210                                  unsigned int boundary,
 211                                  unsigned int timeout)
 212{
 213        unsigned int start_ts;
 214
 215        if (!inet_csk(sk)->icsk_retransmits)
 216                return false;
 217
 218        start_ts = tcp_sk(sk)->retrans_stamp;
 219        if (likely(timeout == 0)) {
 220                unsigned int rto_base = TCP_RTO_MIN;
 221
 222                if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
 223                        rto_base = tcp_timeout_init(sk);
 224                timeout = tcp_model_timeout(sk, boundary, rto_base);
 225        }
 226
 227        return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;
 228}
 229
 230/* A write timeout has occurred. Process the after effects. */
 231static int tcp_write_timeout(struct sock *sk)
 232{
 233        struct inet_connection_sock *icsk = inet_csk(sk);
 234        struct tcp_sock *tp = tcp_sk(sk);
 235        struct net *net = sock_net(sk);
 236        bool expired = false, do_reset;
 237        int retry_until;
 238
 239        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 240                if (icsk->icsk_retransmits)
 241                        __dst_negative_advice(sk);
 242                retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
 243                expired = icsk->icsk_retransmits >= retry_until;
 244        } else {
 245                if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0)) {
 246                        /* Black hole detection */
 247                        tcp_mtu_probing(icsk, sk);
 248
 249                        __dst_negative_advice(sk);
 250                }
 251
 252                retry_until = net->ipv4.sysctl_tcp_retries2;
 253                if (sock_flag(sk, SOCK_DEAD)) {
 254                        const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
 255
 256                        retry_until = tcp_orphan_retries(sk, alive);
 257                        do_reset = alive ||
 258                                !retransmits_timed_out(sk, retry_until, 0);
 259
 260                        if (tcp_out_of_resources(sk, do_reset))
 261                                return 1;
 262                }
 263        }
 264        if (!expired)
 265                expired = retransmits_timed_out(sk, retry_until,
 266                                                icsk->icsk_user_timeout);
 267        tcp_fastopen_active_detect_blackhole(sk, expired);
 268
 269        if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))
 270                tcp_call_bpf_3arg(sk, BPF_SOCK_OPS_RTO_CB,
 271                                  icsk->icsk_retransmits,
 272                                  icsk->icsk_rto, (int)expired);
 273
 274        if (expired) {
 275                /* Has it gone just too far? */
 276                tcp_write_err(sk);
 277                return 1;
 278        }
 279
 280        if (sk_rethink_txhash(sk)) {
 281                tp->timeout_rehash++;
 282                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);
 283        }
 284
 285        return 0;
 286}
 287
 288/* Called with BH disabled */
 289void tcp_delack_timer_handler(struct sock *sk)
 290{
 291        struct inet_connection_sock *icsk = inet_csk(sk);
 292
 293        sk_mem_reclaim_partial(sk);
 294
 295        if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 296            !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 297                goto out;
 298
 299        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 300                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 301                goto out;
 302        }
 303        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 304
 305        if (inet_csk_ack_scheduled(sk)) {
 306                if (!inet_csk_in_pingpong_mode(sk)) {
 307                        /* Delayed ACK missed: inflate ATO. */
 308                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 309                } else {
 310                        /* Delayed ACK missed: leave pingpong mode and
 311                         * deflate ATO.
 312                         */
 313                        inet_csk_exit_pingpong_mode(sk);
 314                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 315                }
 316                tcp_mstamp_refresh(tcp_sk(sk));
 317                tcp_send_ack(sk);
 318                __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 319        }
 320
 321out:
 322        if (tcp_under_memory_pressure(sk))
 323                sk_mem_reclaim(sk);
 324}
 325
 326
 327/**
 328 *  tcp_delack_timer() - The TCP delayed ACK timeout handler
 329 *  @t:  Pointer to the timer. (gets casted to struct sock *)
 330 *
 331 *  This function gets (indirectly) called when the kernel timer for a TCP packet
 332 *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
 333 *
 334 *  Returns: Nothing (void)
 335 */
 336static void tcp_delack_timer(struct timer_list *t)
 337{
 338        struct inet_connection_sock *icsk =
 339                        from_timer(icsk, t, icsk_delack_timer);
 340        struct sock *sk = &icsk->icsk_inet.sk;
 341
 342        bh_lock_sock(sk);
 343        if (!sock_owned_by_user(sk)) {
 344                tcp_delack_timer_handler(sk);
 345        } else {
 346                __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 347                /* deleguate our work to tcp_release_cb() */
 348                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
 349                        sock_hold(sk);
 350        }
 351        bh_unlock_sock(sk);
 352        sock_put(sk);
 353}
 354
 355static void tcp_probe_timer(struct sock *sk)
 356{
 357        struct inet_connection_sock *icsk = inet_csk(sk);
 358        struct sk_buff *skb = tcp_send_head(sk);
 359        struct tcp_sock *tp = tcp_sk(sk);
 360        int max_probes;
 361
 362        if (tp->packets_out || !skb) {
 363                icsk->icsk_probes_out = 0;
 364                icsk->icsk_probes_tstamp = 0;
 365                return;
 366        }
 367
 368        /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 369         * long as the receiver continues to respond probes. We support this by
 370         * default and reset icsk_probes_out with incoming ACKs. But if the
 371         * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 372         * kill the socket when the retry count and the time exceeds the
 373         * corresponding system limit. We also implement similar policy when
 374         * we use RTO to probe window in tcp_retransmit_timer().
 375         */
 376        if (!icsk->icsk_probes_tstamp)
 377                icsk->icsk_probes_tstamp = tcp_jiffies32;
 378        else if (icsk->icsk_user_timeout &&
 379                 (s32)(tcp_jiffies32 - icsk->icsk_probes_tstamp) >=
 380                 msecs_to_jiffies(icsk->icsk_user_timeout))
 381                goto abort;
 382
 383        max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
 384        if (sock_flag(sk, SOCK_DEAD)) {
 385                const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 386
 387                max_probes = tcp_orphan_retries(sk, alive);
 388                if (!alive && icsk->icsk_backoff >= max_probes)
 389                        goto abort;
 390                if (tcp_out_of_resources(sk, true))
 391                        return;
 392        }
 393
 394        if (icsk->icsk_probes_out >= max_probes) {
 395abort:          tcp_write_err(sk);
 396        } else {
 397                /* Only send another probe if we didn't close things up. */
 398                tcp_send_probe0(sk);
 399        }
 400}
 401
 402/*
 403 *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 404 *      sk here is the child socket, not the parent (listener) socket.
 405 */
 406static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req)
 407{
 408        struct inet_connection_sock *icsk = inet_csk(sk);
 409        int max_retries = icsk->icsk_syn_retries ? :
 410            sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 411        struct tcp_sock *tp = tcp_sk(sk);
 412
 413        req->rsk_ops->syn_ack_timeout(req);
 414
 415        if (req->num_timeout >= max_retries) {
 416                tcp_write_err(sk);
 417                return;
 418        }
 419        /* Lower cwnd after certain SYNACK timeout like tcp_init_transfer() */
 420        if (icsk->icsk_retransmits == 1)
 421                tcp_enter_loss(sk);
 422        /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 423         * returned from rtx_syn_ack() to make it more persistent like
 424         * regular retransmit because if the child socket has been accepted
 425         * it's not good to give up too easily.
 426         */
 427        inet_rtx_syn_ack(sk, req);
 428        req->num_timeout++;
 429        icsk->icsk_retransmits++;
 430        if (!tp->retrans_stamp)
 431                tp->retrans_stamp = tcp_time_stamp(tp);
 432        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 433                          TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 434}
 435
 436
 437/**
 438 *  tcp_retransmit_timer() - The TCP retransmit timeout handler
 439 *  @sk:  Pointer to the current socket.
 440 *
 441 *  This function gets called when the kernel timer for a TCP packet
 442 *  of this socket expires.
 443 *
 444 *  It handles retransmission, timer adjustment and other necessary measures.
 445 *
 446 *  Returns: Nothing (void)
 447 */
 448void tcp_retransmit_timer(struct sock *sk)
 449{
 450        struct tcp_sock *tp = tcp_sk(sk);
 451        struct net *net = sock_net(sk);
 452        struct inet_connection_sock *icsk = inet_csk(sk);
 453        struct request_sock *req;
 454        struct sk_buff *skb;
 455
 456        req = rcu_dereference_protected(tp->fastopen_rsk,
 457                                        lockdep_sock_is_held(sk));
 458        if (req) {
 459                WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 460                             sk->sk_state != TCP_FIN_WAIT1);
 461                tcp_fastopen_synack_timer(sk, req);
 462                /* Before we receive ACK to our SYN-ACK don't retransmit
 463                 * anything else (e.g., data or FIN segments).
 464                 */
 465                return;
 466        }
 467
 468        if (!tp->packets_out)
 469                return;
 470
 471        skb = tcp_rtx_queue_head(sk);
 472        if (WARN_ON_ONCE(!skb))
 473                return;
 474
 475        tp->tlp_high_seq = 0;
 476
 477        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 478            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 479                /* Receiver dastardly shrinks window. Our retransmits
 480                 * become zero probes, but we should not timeout this
 481                 * connection. If the socket is an orphan, time it out,
 482                 * we cannot allow such beasts to hang infinitely.
 483                 */
 484                struct inet_sock *inet = inet_sk(sk);
 485                if (sk->sk_family == AF_INET) {
 486                        net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 487                                            &inet->inet_daddr,
 488                                            ntohs(inet->inet_dport),
 489                                            inet->inet_num,
 490                                            tp->snd_una, tp->snd_nxt);
 491                }
 492#if IS_ENABLED(CONFIG_IPV6)
 493                else if (sk->sk_family == AF_INET6) {
 494                        net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 495                                            &sk->sk_v6_daddr,
 496                                            ntohs(inet->inet_dport),
 497                                            inet->inet_num,
 498                                            tp->snd_una, tp->snd_nxt);
 499                }
 500#endif
 501                if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) {
 502                        tcp_write_err(sk);
 503                        goto out;
 504                }
 505                tcp_enter_loss(sk);
 506                tcp_retransmit_skb(sk, skb, 1);
 507                __sk_dst_reset(sk);
 508                goto out_reset_timer;
 509        }
 510
 511        __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 512        if (tcp_write_timeout(sk))
 513                goto out;
 514
 515        if (icsk->icsk_retransmits == 0) {
 516                int mib_idx = 0;
 517
 518                if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 519                        if (tcp_is_sack(tp))
 520                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 521                        else
 522                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 523                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 524                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 525                } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 526                           tp->sacked_out) {
 527                        if (tcp_is_sack(tp))
 528                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 529                        else
 530                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 531                }
 532                if (mib_idx)
 533                        __NET_INC_STATS(sock_net(sk), mib_idx);
 534        }
 535
 536        tcp_enter_loss(sk);
 537
 538        icsk->icsk_retransmits++;
 539        if (tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1) > 0) {
 540                /* Retransmission failed because of local congestion,
 541                 * Let senders fight for local resources conservatively.
 542                 */
 543                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 544                                          TCP_RESOURCE_PROBE_INTERVAL,
 545                                          TCP_RTO_MAX);
 546                goto out;
 547        }
 548
 549        /* Increase the timeout each time we retransmit.  Note that
 550         * we do not increase the rtt estimate.  rto is initialized
 551         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 552         * that doubling rto each time is the least we can get away with.
 553         * In KA9Q, Karn uses this for the first few times, and then
 554         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 555         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 556         * defined in the protocol as the maximum possible RTT.  I guess
 557         * we'll have to use something other than TCP to talk to the
 558         * University of Mars.
 559         *
 560         * PAWS allows us longer timeouts and large windows, so once
 561         * implemented ftp to mars will work nicely. We will have to fix
 562         * the 120 second clamps though!
 563         */
 564        icsk->icsk_backoff++;
 565
 566out_reset_timer:
 567        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 568         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 569         * might be increased if the stream oscillates between thin and thick,
 570         * thus the old value might already be too high compared to the value
 571         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 572         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 573         * exponential backoff behaviour to avoid continue hammering
 574         * linear-timeout retransmissions into a black hole
 575         */
 576        if (sk->sk_state == TCP_ESTABLISHED &&
 577            (tp->thin_lto || net->ipv4.sysctl_tcp_thin_linear_timeouts) &&
 578            tcp_stream_is_thin(tp) &&
 579            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 580                icsk->icsk_backoff = 0;
 581                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 582        } else {
 583                /* Use normal (exponential) backoff */
 584                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 585        }
 586        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 587                                  tcp_clamp_rto_to_user_timeout(sk), TCP_RTO_MAX);
 588        if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0))
 589                __sk_dst_reset(sk);
 590
 591out:;
 592}
 593
 594/* Called with bottom-half processing disabled.
 595   Called by tcp_write_timer() */
 596void tcp_write_timer_handler(struct sock *sk)
 597{
 598        struct inet_connection_sock *icsk = inet_csk(sk);
 599        int event;
 600
 601        if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 602            !icsk->icsk_pending)
 603                goto out;
 604
 605        if (time_after(icsk->icsk_timeout, jiffies)) {
 606                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 607                goto out;
 608        }
 609
 610        tcp_mstamp_refresh(tcp_sk(sk));
 611        event = icsk->icsk_pending;
 612
 613        switch (event) {
 614        case ICSK_TIME_REO_TIMEOUT:
 615                tcp_rack_reo_timeout(sk);
 616                break;
 617        case ICSK_TIME_LOSS_PROBE:
 618                tcp_send_loss_probe(sk);
 619                break;
 620        case ICSK_TIME_RETRANS:
 621                icsk->icsk_pending = 0;
 622                tcp_retransmit_timer(sk);
 623                break;
 624        case ICSK_TIME_PROBE0:
 625                icsk->icsk_pending = 0;
 626                tcp_probe_timer(sk);
 627                break;
 628        }
 629
 630out:
 631        sk_mem_reclaim(sk);
 632}
 633
 634static void tcp_write_timer(struct timer_list *t)
 635{
 636        struct inet_connection_sock *icsk =
 637                        from_timer(icsk, t, icsk_retransmit_timer);
 638        struct sock *sk = &icsk->icsk_inet.sk;
 639
 640        bh_lock_sock(sk);
 641        if (!sock_owned_by_user(sk)) {
 642                tcp_write_timer_handler(sk);
 643        } else {
 644                /* delegate our work to tcp_release_cb() */
 645                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags))
 646                        sock_hold(sk);
 647        }
 648        bh_unlock_sock(sk);
 649        sock_put(sk);
 650}
 651
 652void tcp_syn_ack_timeout(const struct request_sock *req)
 653{
 654        struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
 655
 656        __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
 657}
 658EXPORT_SYMBOL(tcp_syn_ack_timeout);
 659
 660void tcp_set_keepalive(struct sock *sk, int val)
 661{
 662        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 663                return;
 664
 665        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 666                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 667        else if (!val)
 668                inet_csk_delete_keepalive_timer(sk);
 669}
 670EXPORT_SYMBOL_GPL(tcp_set_keepalive);
 671
 672
 673static void tcp_keepalive_timer (struct timer_list *t)
 674{
 675        struct sock *sk = from_timer(sk, t, sk_timer);
 676        struct inet_connection_sock *icsk = inet_csk(sk);
 677        struct tcp_sock *tp = tcp_sk(sk);
 678        u32 elapsed;
 679
 680        /* Only process if socket is not in use. */
 681        bh_lock_sock(sk);
 682        if (sock_owned_by_user(sk)) {
 683                /* Try again later. */
 684                inet_csk_reset_keepalive_timer (sk, HZ/20);
 685                goto out;
 686        }
 687
 688        if (sk->sk_state == TCP_LISTEN) {
 689                pr_err("Hmm... keepalive on a LISTEN ???\n");
 690                goto out;
 691        }
 692
 693        tcp_mstamp_refresh(tp);
 694        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 695                if (tp->linger2 >= 0) {
 696                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 697
 698                        if (tmo > 0) {
 699                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 700                                goto out;
 701                        }
 702                }
 703                tcp_send_active_reset(sk, GFP_ATOMIC);
 704                goto death;
 705        }
 706
 707        if (!sock_flag(sk, SOCK_KEEPOPEN) ||
 708            ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
 709                goto out;
 710
 711        elapsed = keepalive_time_when(tp);
 712
 713        /* It is alive without keepalive 8) */
 714        if (tp->packets_out || !tcp_write_queue_empty(sk))
 715                goto resched;
 716
 717        elapsed = keepalive_time_elapsed(tp);
 718
 719        if (elapsed >= keepalive_time_when(tp)) {
 720                /* If the TCP_USER_TIMEOUT option is enabled, use that
 721                 * to determine when to timeout instead.
 722                 */
 723                if ((icsk->icsk_user_timeout != 0 &&
 724                    elapsed >= msecs_to_jiffies(icsk->icsk_user_timeout) &&
 725                    icsk->icsk_probes_out > 0) ||
 726                    (icsk->icsk_user_timeout == 0 &&
 727                    icsk->icsk_probes_out >= keepalive_probes(tp))) {
 728                        tcp_send_active_reset(sk, GFP_ATOMIC);
 729                        tcp_write_err(sk);
 730                        goto out;
 731                }
 732                if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
 733                        icsk->icsk_probes_out++;
 734                        elapsed = keepalive_intvl_when(tp);
 735                } else {
 736                        /* If keepalive was lost due to local congestion,
 737                         * try harder.
 738                         */
 739                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 740                }
 741        } else {
 742                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 743                elapsed = keepalive_time_when(tp) - elapsed;
 744        }
 745
 746        sk_mem_reclaim(sk);
 747
 748resched:
 749        inet_csk_reset_keepalive_timer (sk, elapsed);
 750        goto out;
 751
 752death:
 753        tcp_done(sk);
 754
 755out:
 756        bh_unlock_sock(sk);
 757        sock_put(sk);
 758}
 759
 760static enum hrtimer_restart tcp_compressed_ack_kick(struct hrtimer *timer)
 761{
 762        struct tcp_sock *tp = container_of(timer, struct tcp_sock, compressed_ack_timer);
 763        struct sock *sk = (struct sock *)tp;
 764
 765        bh_lock_sock(sk);
 766        if (!sock_owned_by_user(sk)) {
 767                if (tp->compressed_ack) {
 768                        /* Since we have to send one ack finally,
 769                         * subtract one from tp->compressed_ack to keep
 770                         * LINUX_MIB_TCPACKCOMPRESSED accurate.
 771                         */
 772                        tp->compressed_ack--;
 773                        tcp_send_ack(sk);
 774                }
 775        } else {
 776                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED,
 777                                      &sk->sk_tsq_flags))
 778                        sock_hold(sk);
 779        }
 780        bh_unlock_sock(sk);
 781
 782        sock_put(sk);
 783
 784        return HRTIMER_NORESTART;
 785}
 786
 787void tcp_init_xmit_timers(struct sock *sk)
 788{
 789        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 790                                  &tcp_keepalive_timer);
 791        hrtimer_init(&tcp_sk(sk)->pacing_timer, CLOCK_MONOTONIC,
 792                     HRTIMER_MODE_ABS_PINNED_SOFT);
 793        tcp_sk(sk)->pacing_timer.function = tcp_pace_kick;
 794
 795        hrtimer_init(&tcp_sk(sk)->compressed_ack_timer, CLOCK_MONOTONIC,
 796                     HRTIMER_MODE_REL_PINNED_SOFT);
 797        tcp_sk(sk)->compressed_ack_timer.function = tcp_compressed_ack_kick;
 798}
 799