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 static 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(!try_module_get(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         module_put(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 (!try_module_get(ca->owner)) {
 226                 ret = -EBUSY;
 227         } else {
 228                 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
 229                 if (prev)
 230                         module_put(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         rcu_read_unlock();
 261 }
 262
 263 /* Get current default congestion control */
 264 void tcp_get_default_congestion_control(struct net *net, char *name)
 265 {
 266         const struct tcp_congestion_ops *ca;
 267
 268         rcu_read_lock();
 269         ca = rcu_dereference(net->ipv4.tcp_congestion_control);
 270         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 271         rcu_read_unlock();
 272 }
 273
 274 /* Built list of non-restricted congestion control values */
 275 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 276 {
 277         struct tcp_congestion_ops *ca;
 278         size_t offs = 0;
 279
 280         *buf = '\0';
 281         rcu_read_lock();
 282         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 283                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 284                         continue;
 285                 offs += snprintf(buf + offs, maxlen - offs,
 286                                  "%s%s",
 287                                  offs == 0 ? "" : " ", ca->name);
 288         }
 289         rcu_read_unlock();
 290 }
 291
 292 /* Change list of non-restricted congestion control */
 293 int tcp_set_allowed_congestion_control(char *val)
 294 {
 295         struct tcp_congestion_ops *ca;
 296         char *saved_clone, *clone, *name;
 297         int ret = 0;
 298
 299         saved_clone = clone = kstrdup(val, GFP_USER);
 300         if (!clone)
 301                 return -ENOMEM;
 302
 303         spin_lock(&tcp_cong_list_lock);
 304         /* pass 1 check for bad entries */
 305         while ((name = strsep(&clone, " ")) && *name) {
 306                 ca = tcp_ca_find(name);
 307                 if (!ca) {
 308                         ret = -ENOENT;
 309                         goto out;
 310                 }
 311         }
 312
 313         /* pass 2 clear old values */
 314         list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 315                 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 316
 317         /* pass 3 mark as allowed */
 318         while ((name = strsep(&val, " ")) && *name) {
 319                 ca = tcp_ca_find(name);
 320                 WARN_ON(!ca);
 321                 if (ca)
 322                         ca->flags |= TCP_CONG_NON_RESTRICTED;
 323         }
 324 out:
 325         spin_unlock(&tcp_cong_list_lock);
 326         kfree(saved_clone);
 327
 328         return ret;
 329 }
 330
 331 /* Change congestion control for socket. If load is false, then it is the
 332  * responsibility of the caller to call tcp_init_congestion_control or
 333  * tcp_reinit_congestion_control (if the current congestion control was
 334  * already initialized.
 335  */
 336 int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit)
 337 {
 338         struct inet_connection_sock *icsk = inet_csk(sk);
 339         const struct tcp_congestion_ops *ca;
 340         int err = 0;
 341
 342         if (icsk->icsk_ca_dst_locked)
 343                 return -EPERM;
 344
 345         rcu_read_lock();
 346         if (!load)
 347                 ca = tcp_ca_find(name);
 348         else
 349                 ca = tcp_ca_find_autoload(sock_net(sk), name);
 350
 351         /* No change asking for existing value */
 352         if (ca == icsk->icsk_ca_ops) {
 353                 icsk->icsk_ca_setsockopt = 1;
 354                 goto out;
 355         }
 356
 357         if (!ca) {
 358                 err = -ENOENT;
 359         } else if (!load) {
 360                 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
 361
 362                 if (try_module_get(ca->owner)) {
 363                         if (reinit) {
 364                                 tcp_reinit_congestion_control(sk, ca);
 365                         } else {
 366                                 icsk->icsk_ca_ops = ca;
 367                                 module_put(old_ca->owner);
 368                         }
 369                 } else {
 370                         err = -EBUSY;
 371                 }
 372         } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
 373                      ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
 374                 err = -EPERM;
 375         } else if (!try_module_get(ca->owner)) {
 376                 err = -EBUSY;
 377         } else {
 378                 tcp_reinit_congestion_control(sk, ca);
 379         }
 380  out:
 381         rcu_read_unlock();
 382         return err;
 383 }
 384
 385 /* Slow start is used when congestion window is no greater than the slow start
 386  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 387  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 388  * something better;) a packet is only considered (s)acked in its entirety to
 389  * defend the ACK attacks described in the RFC. Slow start processes a stretch
 390  * ACK of degree N as if N acks of degree 1 are received back to back except
 391  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 392  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 393  */
 394 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 395 {
 396         u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
 397
 398         acked -= cwnd - tp->snd_cwnd;
 399         tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 400
 401         return acked;
 402 }
 403 EXPORT_SYMBOL_GPL(tcp_slow_start);
 404
 405 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
 406  * for every packet that was ACKed.
 407  */
 408 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
 409 {
 410         /* If credits accumulated at a higher w, apply them gently now. */
 411         if (tp->snd_cwnd_cnt >= w) {
 412                 tp->snd_cwnd_cnt = 0;
 413                 tp->snd_cwnd++;
 414         }
 415
 416         tp->snd_cwnd_cnt += acked;
 417         if (tp->snd_cwnd_cnt >= w) {
 418                 u32 delta = tp->snd_cwnd_cnt / w;
 419
 420                 tp->snd_cwnd_cnt -= delta * w;
 421                 tp->snd_cwnd += delta;
 422         }
 423         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
 424 }
 425 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 426
 427 /*
 428  * TCP Reno congestion control
 429  * This is special case used for fallback as well.
 430  */
 431 /* This is Jacobson's slow start and congestion avoidance.
 432  * SIGCOMM '88, p. 328.
 433  */
 434 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 435 {
 436         struct tcp_sock *tp = tcp_sk(sk);
 437
 438         if (!tcp_is_cwnd_limited(sk))
 439                 return;
 440
 441         /* In "safe" area, increase. */
 442         if (tcp_in_slow_start(tp)) {
 443                 acked = tcp_slow_start(tp, acked);
 444                 if (!acked)
 445                         return;
 446         }
 447         /* In dangerous area, increase slowly. */
 448         tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 449 }
 450 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 451
 452 /* Slow start threshold is half the congestion window (min 2) */
 453 u32 tcp_reno_ssthresh(struct sock *sk)
 454 {
 455         const struct tcp_sock *tp = tcp_sk(sk);
 456
 457         return max(tp->snd_cwnd >> 1U, 2U);
 458 }
 459 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 460
 461 u32 tcp_reno_undo_cwnd(struct sock *sk)
 462 {
 463         const struct tcp_sock *tp = tcp_sk(sk);
 464
 465         return max(tp->snd_cwnd, tp->prior_cwnd);
 466 }
 467 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
 468
 469 struct tcp_congestion_ops tcp_reno = {
 470         .flags          = TCP_CONG_NON_RESTRICTED,
 471         .name           = "reno",
 472         .owner          = THIS_MODULE,
 473         .ssthresh       = tcp_reno_ssthresh,
 474         .cong_avoid     = tcp_reno_cong_avoid,
 475         .undo_cwnd      = tcp_reno_undo_cwnd,
 476 };