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 const struct tcp_congestion_ops *__tcp_ca_find_autoload(const char *name)
  37 {
  38         const struct tcp_congestion_ops *ca = tcp_ca_find(name);
  39 #ifdef CONFIG_MODULES
  40         if (!ca && capable(CAP_NET_ADMIN)) {
  41                 rcu_read_unlock();
  42                 request_module("tcp_%s", name);
  43                 rcu_read_lock();
  44                 ca = tcp_ca_find(name);
  45         }
  46 #endif
  47         return ca;
  48 }
  49
  50 /* Simple linear search, not much in here. */
  51 struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
  52 {
  53         struct tcp_congestion_ops *e;
  54
  55         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
  56                 if (e->key == key)
  57                         return e;
  58         }
  59
  60         return NULL;
  61 }
  62
  63 /*
  64  * Attach new congestion control algorithm to the list
  65  * of available options.
  66  */
  67 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
  68 {
  69         int ret = 0;
  70
  71         /* all algorithms must implement ssthresh and cong_avoid ops */
  72         if (!ca->ssthresh || !ca->cong_avoid) {
  73                 pr_err("%s does not implement required ops\n", ca->name);
  74                 return -EINVAL;
  75         }
  76
  77         ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
  78
  79         spin_lock(&tcp_cong_list_lock);
  80         if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
  81                 pr_notice("%s already registered or non-unique key\n",
  82                           ca->name);
  83                 ret = -EEXIST;
  84         } else {
  85                 list_add_tail_rcu(&ca->list, &tcp_cong_list);
  86                 pr_debug("%s registered\n", ca->name);
  87         }
  88         spin_unlock(&tcp_cong_list_lock);
  89
  90         return ret;
  91 }
  92 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
  93
  94 /*
  95  * Remove congestion control algorithm, called from
  96  * the module's remove function.  Module ref counts are used
  97  * to ensure that this can't be done till all sockets using
  98  * that method are closed.
  99  */
 100 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 101 {
 102         spin_lock(&tcp_cong_list_lock);
 103         list_del_rcu(&ca->list);
 104         spin_unlock(&tcp_cong_list_lock);
 105
 106         /* Wait for outstanding readers to complete before the
 107          * module gets removed entirely.
 108          *
 109          * A try_module_get() should fail by now as our module is
 110          * in "going" state since no refs are held anymore and
 111          * module_exit() handler being called.
 112          */
 113         synchronize_rcu();
 114 }
 115 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
 116
 117 u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
 118 {
 119         const struct tcp_congestion_ops *ca;
 120         u32 key = TCP_CA_UNSPEC;
 121
 122         might_sleep();
 123
 124         rcu_read_lock();
 125         ca = __tcp_ca_find_autoload(name);
 126         if (ca) {
 127                 key = ca->key;
 128                 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
 129         }
 130         rcu_read_unlock();
 131
 132         return key;
 133 }
 134 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
 135
 136 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
 137 {
 138         const struct tcp_congestion_ops *ca;
 139         char *ret = NULL;
 140
 141         rcu_read_lock();
 142         ca = tcp_ca_find_key(key);
 143         if (ca)
 144                 ret = strncpy(buffer, ca->name,
 145                               TCP_CA_NAME_MAX);
 146         rcu_read_unlock();
 147
 148         return ret;
 149 }
 150 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
 151
 152 /* Assign choice of congestion control. */
 153 void tcp_assign_congestion_control(struct sock *sk)
 154 {
 155         struct inet_connection_sock *icsk = inet_csk(sk);
 156         struct tcp_congestion_ops *ca;
 157
 158         rcu_read_lock();
 159         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 160                 if (likely(try_module_get(ca->owner))) {
 161                         icsk->icsk_ca_ops = ca;
 162                         goto out;
 163                 }
 164                 /* Fallback to next available. The last really
 165                  * guaranteed fallback is Reno from this list.
 166                  */
 167         }
 168 out:
 169         rcu_read_unlock();
 170
 171         /* Clear out private data before diag gets it and
 172          * the ca has not been initialized.
 173          */
 174         if (ca->get_info)
 175                 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
 176         if (ca->flags & TCP_CONG_NEEDS_ECN)
 177                 INET_ECN_xmit(sk);
 178         else
 179                 INET_ECN_dontxmit(sk);
 180 }
 181
 182 void tcp_init_congestion_control(struct sock *sk)
 183 {
 184         const struct inet_connection_sock *icsk = inet_csk(sk);
 185
 186         if (icsk->icsk_ca_ops->init)
 187                 icsk->icsk_ca_ops->init(sk);
 188         if (tcp_ca_needs_ecn(sk))
 189                 INET_ECN_xmit(sk);
 190         else
 191                 INET_ECN_dontxmit(sk);
 192 }
 193
 194 static void tcp_reinit_congestion_control(struct sock *sk,
 195                                           const struct tcp_congestion_ops *ca)
 196 {
 197         struct inet_connection_sock *icsk = inet_csk(sk);
 198
 199         tcp_cleanup_congestion_control(sk);
 200         icsk->icsk_ca_ops = ca;
 201         icsk->icsk_ca_setsockopt = 1;
 202
 203         if (sk->sk_state != TCP_CLOSE)
 204                 tcp_init_congestion_control(sk);
 205 }
 206
 207 /* Manage refcounts on socket close. */
 208 void tcp_cleanup_congestion_control(struct sock *sk)
 209 {
 210         struct inet_connection_sock *icsk = inet_csk(sk);
 211
 212         if (icsk->icsk_ca_ops->release)
 213                 icsk->icsk_ca_ops->release(sk);
 214         module_put(icsk->icsk_ca_ops->owner);
 215 }
 216
 217 /* Used by sysctl to change default congestion control */
 218 int tcp_set_default_congestion_control(const char *name)
 219 {
 220         struct tcp_congestion_ops *ca;
 221         int ret = -ENOENT;
 222
 223         spin_lock(&tcp_cong_list_lock);
 224         ca = tcp_ca_find(name);
 225 #ifdef CONFIG_MODULES
 226         if (!ca && capable(CAP_NET_ADMIN)) {
 227                 spin_unlock(&tcp_cong_list_lock);
 228
 229                 request_module("tcp_%s", name);
 230                 spin_lock(&tcp_cong_list_lock);
 231                 ca = tcp_ca_find(name);
 232         }
 233 #endif
 234
 235         if (ca) {
 236                 ca->flags |= TCP_CONG_NON_RESTRICTED;   /* default is always allowed */
 237                 list_move(&ca->list, &tcp_cong_list);
 238                 ret = 0;
 239         }
 240         spin_unlock(&tcp_cong_list_lock);
 241
 242         return ret;
 243 }
 244
 245 /* Set default value from kernel configuration at bootup */
 246 static int __init tcp_congestion_default(void)
 247 {
 248         return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 249 }
 250 late_initcall(tcp_congestion_default);
 251
 252 /* Build string with list of available congestion control values */
 253 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 254 {
 255         struct tcp_congestion_ops *ca;
 256         size_t offs = 0;
 257
 258         rcu_read_lock();
 259         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 260                 offs += snprintf(buf + offs, maxlen - offs,
 261                                  "%s%s",
 262                                  offs == 0 ? "" : " ", ca->name);
 263         }
 264         rcu_read_unlock();
 265 }
 266
 267 /* Get current default congestion control */
 268 void tcp_get_default_congestion_control(char *name)
 269 {
 270         struct tcp_congestion_ops *ca;
 271         /* We will always have reno... */
 272         BUG_ON(list_empty(&tcp_cong_list));
 273
 274         rcu_read_lock();
 275         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 276         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 277         rcu_read_unlock();
 278 }
 279
 280 /* Built list of non-restricted congestion control values */
 281 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 282 {
 283         struct tcp_congestion_ops *ca;
 284         size_t offs = 0;
 285
 286         *buf = '\0';
 287         rcu_read_lock();
 288         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 289                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 290                         continue;
 291                 offs += snprintf(buf + offs, maxlen - offs,
 292                                  "%s%s",
 293                                  offs == 0 ? "" : " ", ca->name);
 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 */
 338 int tcp_set_congestion_control(struct sock *sk, const char *name)
 339 {
 340         struct inet_connection_sock *icsk = inet_csk(sk);
 341         const struct tcp_congestion_ops *ca;
 342         int err = 0;
 343
 344         if (icsk->icsk_ca_dst_locked)
 345                 return -EPERM;
 346
 347         rcu_read_lock();
 348         ca = __tcp_ca_find_autoload(name);
 349         /* No change asking for existing value */
 350         if (ca == icsk->icsk_ca_ops) {
 351                 icsk->icsk_ca_setsockopt = 1;
 352                 goto out;
 353         }
 354         if (!ca)
 355                 err = -ENOENT;
 356         else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
 357                    ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
 358                 err = -EPERM;
 359         else if (!try_module_get(ca->owner))
 360                 err = -EBUSY;
 361         else
 362                 tcp_reinit_congestion_control(sk, ca);
 363  out:
 364         rcu_read_unlock();
 365         return err;
 366 }
 367
 368 /* Slow start is used when congestion window is no greater than the slow start
 369  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 370  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 371  * something better;) a packet is only considered (s)acked in its entirety to
 372  * defend the ACK attacks described in the RFC. Slow start processes a stretch
 373  * ACK of degree N as if N acks of degree 1 are received back to back except
 374  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 375  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 376  */
 377 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 378 {
 379         u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
 380
 381         acked -= cwnd - tp->snd_cwnd;
 382         tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 383
 384         return acked;
 385 }
 386 EXPORT_SYMBOL_GPL(tcp_slow_start);
 387
 388 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
 389  * for every packet that was ACKed.
 390  */
 391 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
 392 {
 393         /* If credits accumulated at a higher w, apply them gently now. */
 394         if (tp->snd_cwnd_cnt >= w) {
 395                 tp->snd_cwnd_cnt = 0;
 396                 tp->snd_cwnd++;
 397         }
 398
 399         tp->snd_cwnd_cnt += acked;
 400         if (tp->snd_cwnd_cnt >= w) {
 401                 u32 delta = tp->snd_cwnd_cnt / w;
 402
 403                 tp->snd_cwnd_cnt -= delta * w;
 404                 tp->snd_cwnd += delta;
 405         }
 406         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
 407 }
 408 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 409
 410 /*
 411  * TCP Reno congestion control
 412  * This is special case used for fallback as well.
 413  */
 414 /* This is Jacobson's slow start and congestion avoidance.
 415  * SIGCOMM '88, p. 328.
 416  */
 417 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 418 {
 419         struct tcp_sock *tp = tcp_sk(sk);
 420
 421         if (!tcp_is_cwnd_limited(sk))
 422                 return;
 423
 424         /* In "safe" area, increase. */
 425         if (tcp_in_slow_start(tp)) {
 426                 acked = tcp_slow_start(tp, acked);
 427                 if (!acked)
 428                         return;
 429         }
 430         /* In dangerous area, increase slowly. */
 431         tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 432 }
 433 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 434
 435 /* Slow start threshold is half the congestion window (min 2) */
 436 u32 tcp_reno_ssthresh(struct sock *sk)
 437 {
 438         const struct tcp_sock *tp = tcp_sk(sk);
 439
 440         return max(tp->snd_cwnd >> 1U, 2U);
 441 }
 442 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 443
 444 struct tcp_congestion_ops tcp_reno = {
 445         .flags          = TCP_CONG_NON_RESTRICTED,
 446         .name           = "reno",
 447         .owner          = THIS_MODULE,
 448         .ssthresh       = tcp_reno_ssthresh,
 449         .cong_avoid     = tcp_reno_cong_avoid,
 450 };