net/ipv4/tcp_cong.c

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