net/ipv4/tcp_cong.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Pluggable TCP congestion control support and newReno
   4  * congestion control.
   5  * Based on ideas from I/O scheduler support and Web100.
   6  *
   7  * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
   8  */
   9
  10 #define pr_fmt(fmt) "TCP: " fmt
  11
  12 #include <linux/module.h>
  13 #include <linux/mm.h>
  14 #include <linux/types.h>
  15 #include <linux/list.h>
  16 #include <linux/gfp.h>
  17 #include <linux/jhash.h>
  18 #include <net/tcp.h>
  19
  20 static DEFINE_SPINLOCK(tcp_cong_list_lock);
  21 static LIST_HEAD(tcp_cong_list);
  22
  23 /* Simple linear search, don't expect many entries! */
  24 struct tcp_congestion_ops *tcp_ca_find(const char *name)
  25 {
  26         struct tcp_congestion_ops *e;
  27
  28         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
  29                 if (strcmp(e->name, name) == 0)
  30                         return e;
  31         }
  32
  33         return NULL;
  34 }
  35
  36 /* Must be called with rcu lock held */
  37 static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
  38                                                        const char *name)
  39 {
  40         struct tcp_congestion_ops *ca = tcp_ca_find(name);
  41
  42 #ifdef CONFIG_MODULES
  43         if (!ca && capable(CAP_NET_ADMIN)) {
  44                 rcu_read_unlock();
  45                 request_module("tcp_%s", name);
  46                 rcu_read_lock();
  47                 ca = tcp_ca_find(name);
  48         }
  49 #endif
  50         return ca;
  51 }
  52
  53 /* Simple linear search, not much in here. */
  54 struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
  55 {
  56         struct tcp_congestion_ops *e;
  57
  58         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
  59                 if (e->key == key)
  60                         return e;
  61         }
  62
  63         return NULL;
  64 }
  65
  66 /*
  67  * Attach new congestion control algorithm to the list
  68  * of available options.
  69  */
  70 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
  71 {
  72         int ret = 0;
  73
  74         /* all algorithms must implement these */
  75         if (!ca->ssthresh || !ca->undo_cwnd ||
  76             !(ca->cong_avoid || ca->cong_control)) {
  77                 pr_err("%s does not implement required ops\n", ca->name);
  78                 return -EINVAL;
  79         }
  80
  81         ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
  82
  83         spin_lock(&tcp_cong_list_lock);
  84         if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
  85                 pr_notice("%s already registered or non-unique key\n",
  86                           ca->name);
  87                 ret = -EEXIST;
  88         } else {
  89                 list_add_tail_rcu(&ca->list, &tcp_cong_list);
  90                 pr_debug("%s registered\n", ca->name);
  91         }
  92         spin_unlock(&tcp_cong_list_lock);
  93
  94         return ret;
  95 }
  96 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
  97
  98 /*
  99  * Remove congestion control algorithm, called from
 100  * the module's remove function.  Module ref counts are used
 101  * to ensure that this can't be done till all sockets using
 102  * that method are closed.
 103  */
 104 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 105 {
 106         spin_lock(&tcp_cong_list_lock);
 107         list_del_rcu(&ca->list);
 108         spin_unlock(&tcp_cong_list_lock);
 109
 110         /* Wait for outstanding readers to complete before the
 111          * module gets removed entirely.
 112          *
 113          * A try_module_get() should fail by now as our module is
 114          * in "going" state since no refs are held anymore and
 115          * module_exit() handler being called.
 116          */
 117         synchronize_rcu();
 118 }
 119 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
 120
 121 u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
 122 {
 123         const struct tcp_congestion_ops *ca;
 124         u32 key = TCP_CA_UNSPEC;
 125
 126         might_sleep();
 127
 128         rcu_read_lock();
 129         ca = tcp_ca_find_autoload(net, name);
 130         if (ca) {
 131                 key = ca->key;
 132                 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
 133         }
 134         rcu_read_unlock();
 135
 136         return key;
 137 }
 138 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
 139
 140 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
 141 {
 142         const struct tcp_congestion_ops *ca;
 143         char *ret = NULL;
 144
 145         rcu_read_lock();
 146         ca = tcp_ca_find_key(key);
 147         if (ca)
 148                 ret = strncpy(buffer, ca->name,
 149                               TCP_CA_NAME_MAX);
 150         rcu_read_unlock();
 151
 152         return ret;
 153 }
 154 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
 155
 156 /* Assign choice of congestion control. */
 157 void tcp_assign_congestion_control(struct sock *sk)
 158 {
 159         struct net *net = sock_net(sk);
 160         struct inet_connection_sock *icsk = inet_csk(sk);
 161         const struct tcp_congestion_ops *ca;
 162
 163         rcu_read_lock();
 164         ca = rcu_dereference(net->ipv4.tcp_congestion_control);
 165         if (unlikely(!bpf_try_module_get(ca, ca->owner)))
 166                 ca = &tcp_reno;
 167         icsk->icsk_ca_ops = ca;
 168         rcu_read_unlock();
 169
 170         memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
 171         if (ca->flags & TCP_CONG_NEEDS_ECN)
 172                 INET_ECN_xmit(sk);
 173         else
 174                 INET_ECN_dontxmit(sk);
 175 }
 176
 177 void tcp_init_congestion_control(struct sock *sk)
 178 {
 179         const struct inet_connection_sock *icsk = inet_csk(sk);
 180
 181         tcp_sk(sk)->prior_ssthresh = 0;
 182         if (icsk->icsk_ca_ops->init)
 183                 icsk->icsk_ca_ops->init(sk);
 184         if (tcp_ca_needs_ecn(sk))
 185                 INET_ECN_xmit(sk);
 186         else
 187                 INET_ECN_dontxmit(sk);
 188 }
 189
 190 static void tcp_reinit_congestion_control(struct sock *sk,
 191                                           const struct tcp_congestion_ops *ca)
 192 {
 193         struct inet_connection_sock *icsk = inet_csk(sk);
 194
 195         tcp_cleanup_congestion_control(sk);
 196         icsk->icsk_ca_ops = ca;
 197         icsk->icsk_ca_setsockopt = 1;
 198         memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
 199
 200         if (sk->sk_state != TCP_CLOSE)
 201                 tcp_init_congestion_control(sk);
 202 }
 203
 204 /* Manage refcounts on socket close. */
 205 void tcp_cleanup_congestion_control(struct sock *sk)
 206 {
 207         struct inet_connection_sock *icsk = inet_csk(sk);
 208
 209         if (icsk->icsk_ca_ops->release)
 210                 icsk->icsk_ca_ops->release(sk);
 211         bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
 212 }
 213
 214 /* Used by sysctl to change default congestion control */
 215 int tcp_set_default_congestion_control(struct net *net, const char *name)
 216 {
 217         struct tcp_congestion_ops *ca;
 218         const struct tcp_congestion_ops *prev;
 219         int ret;
 220
 221         rcu_read_lock();
 222         ca = tcp_ca_find_autoload(net, name);
 223         if (!ca) {
 224                 ret = -ENOENT;
 225         } else if (!bpf_try_module_get(ca, ca->owner)) {
 226                 ret = -EBUSY;
 227         } else {
 228                 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
 229                 if (prev)
 230                         bpf_module_put(prev, prev->owner);
 231
 232                 ca->flags |= TCP_CONG_NON_RESTRICTED;
 233                 ret = 0;
 234         }
 235         rcu_read_unlock();
 236
 237         return ret;
 238 }
 239
 240 /* Set default value from kernel configuration at bootup */
 241 static int __init tcp_congestion_default(void)
 242 {
 243         return tcp_set_default_congestion_control(&init_net,
 244                                                   CONFIG_DEFAULT_TCP_CONG);
 245 }
 246 late_initcall(tcp_congestion_default);
 247
 248 /* Build string with list of available congestion control values */
 249 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 250 {
 251         struct tcp_congestion_ops *ca;
 252         size_t offs = 0;
 253
 254         rcu_read_lock();
 255         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 256                 offs += snprintf(buf + offs, maxlen - offs,
 257                                  "%s%s",
 258                                  offs == 0 ? "" : " ", ca->name);
 259
 260                 if (WARN_ON_ONCE(offs >= maxlen))
 261                         break;
 262         }
 263         rcu_read_unlock();
 264 }
 265
 266 /* Get current default congestion control */
 267 void tcp_get_default_congestion_control(struct net *net, char *name)
 268 {
 269         const struct tcp_congestion_ops *ca;
 270
 271         rcu_read_lock();
 272         ca = rcu_dereference(net->ipv4.tcp_congestion_control);
 273         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 274         rcu_read_unlock();
 275 }
 276
 277 /* Built list of non-restricted congestion control values */
 278 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 279 {
 280         struct tcp_congestion_ops *ca;
 281         size_t offs = 0;
 282
 283         *buf = '\0';
 284         rcu_read_lock();
 285         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 286                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 287                         continue;
 288                 offs += snprintf(buf + offs, maxlen - offs,
 289                                  "%s%s",
 290                                  offs == 0 ? "" : " ", ca->name);
 291
 292                 if (WARN_ON_ONCE(offs >= maxlen))
 293                         break;
 294         }
 295         rcu_read_unlock();
 296 }
 297
 298 /* Change list of non-restricted congestion control */
 299 int tcp_set_allowed_congestion_control(char *val)
 300 {
 301         struct tcp_congestion_ops *ca;
 302         char *saved_clone, *clone, *name;
 303         int ret = 0;
 304
 305         saved_clone = clone = kstrdup(val, GFP_USER);
 306         if (!clone)
 307                 return -ENOMEM;
 308
 309         spin_lock(&tcp_cong_list_lock);
 310         /* pass 1 check for bad entries */
 311         while ((name = strsep(&clone, " ")) && *name) {
 312                 ca = tcp_ca_find(name);
 313                 if (!ca) {
 314                         ret = -ENOENT;
 315                         goto out;
 316                 }
 317         }
 318
 319         /* pass 2 clear old values */
 320         list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 321                 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 322
 323         /* pass 3 mark as allowed */
 324         while ((name = strsep(&val, " ")) && *name) {
 325                 ca = tcp_ca_find(name);
 326                 WARN_ON(!ca);
 327                 if (ca)
 328                         ca->flags |= TCP_CONG_NON_RESTRICTED;
 329         }
 330 out:
 331         spin_unlock(&tcp_cong_list_lock);
 332         kfree(saved_clone);
 333
 334         return ret;
 335 }
 336
 337 /* Change congestion control for socket. If load is false, then it is the
 338  * responsibility of the caller to call tcp_init_congestion_control or
 339  * tcp_reinit_congestion_control (if the current congestion control was
 340  * already initialized.
 341  */
 342 int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
 343                                bool reinit, bool cap_net_admin)
 344 {
 345         struct inet_connection_sock *icsk = inet_csk(sk);
 346         const struct tcp_congestion_ops *ca;
 347         int err = 0;
 348
 349         if (icsk->icsk_ca_dst_locked)
 350                 return -EPERM;
 351
 352         rcu_read_lock();
 353         if (!load)
 354                 ca = tcp_ca_find(name);
 355         else
 356                 ca = tcp_ca_find_autoload(sock_net(sk), name);
 357
 358         /* No change asking for existing value */
 359         if (ca == icsk->icsk_ca_ops) {
 360                 icsk->icsk_ca_setsockopt = 1;
 361                 goto out;
 362         }
 363
 364         if (!ca) {
 365                 err = -ENOENT;
 366         } else if (!load) {
 367                 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
 368
 369                 if (bpf_try_module_get(ca, ca->owner)) {
 370                         if (reinit) {
 371                                 tcp_reinit_congestion_control(sk, ca);
 372                         } else {
 373                                 icsk->icsk_ca_ops = ca;
 374                                 bpf_module_put(old_ca, old_ca->owner);
 375                         }
 376                 } else {
 377                         err = -EBUSY;
 378                 }
 379         } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin)) {
 380                 err = -EPERM;
 381         } else if (!bpf_try_module_get(ca, ca->owner)) {
 382                 err = -EBUSY;
 383         } else {
 384                 tcp_reinit_congestion_control(sk, ca);
 385         }
 386  out:
 387         rcu_read_unlock();
 388         return err;
 389 }
 390
 391 /* Slow start is used when congestion window is no greater than the slow start
 392  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 393  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 394  * something better;) a packet is only considered (s)acked in its entirety to
 395  * defend the ACK attacks described in the RFC. Slow start processes a stretch
 396  * ACK of degree N as if N acks of degree 1 are received back to back except
 397  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 398  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 399  */
 400 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 401 {
 402         u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
 403
 404         acked -= cwnd - tp->snd_cwnd;
 405         tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 406
 407         return acked;
 408 }
 409 EXPORT_SYMBOL_GPL(tcp_slow_start);
 410
 411 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
 412  * for every packet that was ACKed.
 413  */
 414 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
 415 {
 416         /* If credits accumulated at a higher w, apply them gently now. */
 417         if (tp->snd_cwnd_cnt >= w) {
 418                 tp->snd_cwnd_cnt = 0;
 419                 tp->snd_cwnd++;
 420         }
 421
 422         tp->snd_cwnd_cnt += acked;
 423         if (tp->snd_cwnd_cnt >= w) {
 424                 u32 delta = tp->snd_cwnd_cnt / w;
 425
 426                 tp->snd_cwnd_cnt -= delta * w;
 427                 tp->snd_cwnd += delta;
 428         }
 429         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
 430 }
 431 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 432
 433 /*
 434  * TCP Reno congestion control
 435  * This is special case used for fallback as well.
 436  */
 437 /* This is Jacobson's slow start and congestion avoidance.
 438  * SIGCOMM '88, p. 328.
 439  */
 440 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 441 {
 442         struct tcp_sock *tp = tcp_sk(sk);
 443
 444         if (!tcp_is_cwnd_limited(sk))
 445                 return;
 446
 447         /* In "safe" area, increase. */
 448         if (tcp_in_slow_start(tp)) {
 449                 acked = tcp_slow_start(tp, acked);
 450                 if (!acked)
 451                         return;
 452         }
 453         /* In dangerous area, increase slowly. */
 454         tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 455 }
 456 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 457
 458 /* Slow start threshold is half the congestion window (min 2) */
 459 u32 tcp_reno_ssthresh(struct sock *sk)
 460 {
 461         const struct tcp_sock *tp = tcp_sk(sk);
 462
 463         return max(tp->snd_cwnd >> 1U, 2U);
 464 }
 465 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 466
 467 u32 tcp_reno_undo_cwnd(struct sock *sk)
 468 {
 469         const struct tcp_sock *tp = tcp_sk(sk);
 470
 471         return max(tp->snd_cwnd, tp->prior_cwnd);
 472 }
 473 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
 474
 475 struct tcp_congestion_ops tcp_reno = {
 476         .flags          = TCP_CONG_NON_RESTRICTED,
 477         .name           = "reno",
 478         .owner          = THIS_MODULE,
 479         .ssthresh       = tcp_reno_ssthresh,
 480         .cong_avoid     = tcp_reno_cong_avoid,
 481         .undo_cwnd      = tcp_reno_undo_cwnd,
 482 };