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)
 118 {
 119         const struct tcp_congestion_ops *ca;
 120         u32 key;
 121
 122         might_sleep();
 123
 124         rcu_read_lock();
 125         ca = __tcp_ca_find_autoload(name);
 126         key = ca ? ca->key : TCP_CA_UNSPEC;
 127         rcu_read_unlock();
 128
 129         return key;
 130 }
 131 EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
 132
 133 char *tcp_ca_get_name_by_key(u32 key, char *buffer)
 134 {
 135         const struct tcp_congestion_ops *ca;
 136         char *ret = NULL;
 137
 138         rcu_read_lock();
 139         ca = tcp_ca_find_key(key);
 140         if (ca)
 141                 ret = strncpy(buffer, ca->name,
 142                               TCP_CA_NAME_MAX);
 143         rcu_read_unlock();
 144
 145         return ret;
 146 }
 147 EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
 148
 149 /* Assign choice of congestion control. */
 150 void tcp_assign_congestion_control(struct sock *sk)
 151 {
 152         struct inet_connection_sock *icsk = inet_csk(sk);
 153         struct tcp_congestion_ops *ca;
 154
 155         rcu_read_lock();
 156         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 157                 if (likely(try_module_get(ca->owner))) {
 158                         icsk->icsk_ca_ops = ca;
 159                         goto out;
 160                 }
 161                 /* Fallback to next available. The last really
 162                  * guaranteed fallback is Reno from this list.
 163                  */
 164         }
 165 out:
 166         rcu_read_unlock();
 167
 168         /* Clear out private data before diag gets it and
 169          * the ca has not been initialized.
 170          */
 171         if (ca->get_info)
 172                 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
 173 }
 174
 175 void tcp_init_congestion_control(struct sock *sk)
 176 {
 177         const struct inet_connection_sock *icsk = inet_csk(sk);
 178
 179         if (icsk->icsk_ca_ops->init)
 180                 icsk->icsk_ca_ops->init(sk);
 181 }
 182
 183 static void tcp_reinit_congestion_control(struct sock *sk,
 184                                           const struct tcp_congestion_ops *ca)
 185 {
 186         struct inet_connection_sock *icsk = inet_csk(sk);
 187
 188         tcp_cleanup_congestion_control(sk);
 189         icsk->icsk_ca_ops = ca;
 190         icsk->icsk_ca_setsockopt = 1;
 191
 192         if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
 193                 icsk->icsk_ca_ops->init(sk);
 194 }
 195
 196 /* Manage refcounts on socket close. */
 197 void tcp_cleanup_congestion_control(struct sock *sk)
 198 {
 199         struct inet_connection_sock *icsk = inet_csk(sk);
 200
 201         if (icsk->icsk_ca_ops->release)
 202                 icsk->icsk_ca_ops->release(sk);
 203         module_put(icsk->icsk_ca_ops->owner);
 204 }
 205
 206 /* Used by sysctl to change default congestion control */
 207 int tcp_set_default_congestion_control(const char *name)
 208 {
 209         struct tcp_congestion_ops *ca;
 210         int ret = -ENOENT;
 211
 212         spin_lock(&tcp_cong_list_lock);
 213         ca = tcp_ca_find(name);
 214 #ifdef CONFIG_MODULES
 215         if (!ca && capable(CAP_NET_ADMIN)) {
 216                 spin_unlock(&tcp_cong_list_lock);
 217
 218                 request_module("tcp_%s", name);
 219                 spin_lock(&tcp_cong_list_lock);
 220                 ca = tcp_ca_find(name);
 221         }
 222 #endif
 223
 224         if (ca) {
 225                 ca->flags |= TCP_CONG_NON_RESTRICTED;   /* default is always allowed */
 226                 list_move(&ca->list, &tcp_cong_list);
 227                 ret = 0;
 228         }
 229         spin_unlock(&tcp_cong_list_lock);
 230
 231         return ret;
 232 }
 233
 234 /* Set default value from kernel configuration at bootup */
 235 static int __init tcp_congestion_default(void)
 236 {
 237         return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 238 }
 239 late_initcall(tcp_congestion_default);
 240
 241 /* Build string with list of available congestion control values */
 242 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 243 {
 244         struct tcp_congestion_ops *ca;
 245         size_t offs = 0;
 246
 247         rcu_read_lock();
 248         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 249                 offs += snprintf(buf + offs, maxlen - offs,
 250                                  "%s%s",
 251                                  offs == 0 ? "" : " ", ca->name);
 252         }
 253         rcu_read_unlock();
 254 }
 255
 256 /* Get current default congestion control */
 257 void tcp_get_default_congestion_control(char *name)
 258 {
 259         struct tcp_congestion_ops *ca;
 260         /* We will always have reno... */
 261         BUG_ON(list_empty(&tcp_cong_list));
 262
 263         rcu_read_lock();
 264         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 265         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 266         rcu_read_unlock();
 267 }
 268
 269 /* Built list of non-restricted congestion control values */
 270 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 271 {
 272         struct tcp_congestion_ops *ca;
 273         size_t offs = 0;
 274
 275         *buf = '\0';
 276         rcu_read_lock();
 277         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 278                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 279                         continue;
 280                 offs += snprintf(buf + offs, maxlen - offs,
 281                                  "%s%s",
 282                                  offs == 0 ? "" : " ", ca->name);
 283         }
 284         rcu_read_unlock();
 285 }
 286
 287 /* Change list of non-restricted congestion control */
 288 int tcp_set_allowed_congestion_control(char *val)
 289 {
 290         struct tcp_congestion_ops *ca;
 291         char *saved_clone, *clone, *name;
 292         int ret = 0;
 293
 294         saved_clone = clone = kstrdup(val, GFP_USER);
 295         if (!clone)
 296                 return -ENOMEM;
 297
 298         spin_lock(&tcp_cong_list_lock);
 299         /* pass 1 check for bad entries */
 300         while ((name = strsep(&clone, " ")) && *name) {
 301                 ca = tcp_ca_find(name);
 302                 if (!ca) {
 303                         ret = -ENOENT;
 304                         goto out;
 305                 }
 306         }
 307
 308         /* pass 2 clear old values */
 309         list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 310                 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 311
 312         /* pass 3 mark as allowed */
 313         while ((name = strsep(&val, " ")) && *name) {
 314                 ca = tcp_ca_find(name);
 315                 WARN_ON(!ca);
 316                 if (ca)
 317                         ca->flags |= TCP_CONG_NON_RESTRICTED;
 318         }
 319 out:
 320         spin_unlock(&tcp_cong_list_lock);
 321         kfree(saved_clone);
 322
 323         return ret;
 324 }
 325
 326 /* Change congestion control for socket */
 327 int tcp_set_congestion_control(struct sock *sk, const char *name)
 328 {
 329         struct inet_connection_sock *icsk = inet_csk(sk);
 330         const struct tcp_congestion_ops *ca;
 331         int err = 0;
 332
 333         if (icsk->icsk_ca_dst_locked)
 334                 return -EPERM;
 335
 336         rcu_read_lock();
 337         ca = __tcp_ca_find_autoload(name);
 338         /* No change asking for existing value */
 339         if (ca == icsk->icsk_ca_ops) {
 340                 icsk->icsk_ca_setsockopt = 1;
 341                 goto out;
 342         }
 343         if (!ca)
 344                 err = -ENOENT;
 345         else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
 346                    ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
 347                 err = -EPERM;
 348         else if (!try_module_get(ca->owner))
 349                 err = -EBUSY;
 350         else
 351                 tcp_reinit_congestion_control(sk, ca);
 352  out:
 353         rcu_read_unlock();
 354         return err;
 355 }
 356
 357 /* Slow start is used when congestion window is no greater than the slow start
 358  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 359  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 360  * something better;) a packet is only considered (s)acked in its entirety to
 361  * defend the ACK attacks described in the RFC. Slow start processes a stretch
 362  * ACK of degree N as if N acks of degree 1 are received back to back except
 363  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 364  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 365  */
 366 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 367 {
 368         u32 cwnd = tp->snd_cwnd + acked;
 369
 370         if (cwnd > tp->snd_ssthresh)
 371                 cwnd = tp->snd_ssthresh + 1;
 372         acked -= cwnd - tp->snd_cwnd;
 373         tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 374
 375         return acked;
 376 }
 377 EXPORT_SYMBOL_GPL(tcp_slow_start);
 378
 379 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
 380  * for every packet that was ACKed.
 381  */
 382 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
 383 {
 384         /* If credits accumulated at a higher w, apply them gently now. */
 385         if (tp->snd_cwnd_cnt >= w) {
 386                 tp->snd_cwnd_cnt = 0;
 387                 tp->snd_cwnd++;
 388         }
 389
 390         tp->snd_cwnd_cnt += acked;
 391         if (tp->snd_cwnd_cnt >= w) {
 392                 u32 delta = tp->snd_cwnd_cnt / w;
 393
 394                 tp->snd_cwnd_cnt -= delta * w;
 395                 tp->snd_cwnd += delta;
 396         }
 397         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
 398 }
 399 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 400
 401 /*
 402  * TCP Reno congestion control
 403  * This is special case used for fallback as well.
 404  */
 405 /* This is Jacobson's slow start and congestion avoidance.
 406  * SIGCOMM '88, p. 328.
 407  */
 408 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 409 {
 410         struct tcp_sock *tp = tcp_sk(sk);
 411
 412         if (!tcp_is_cwnd_limited(sk))
 413                 return;
 414
 415         /* In "safe" area, increase. */
 416         if (tp->snd_cwnd <= tp->snd_ssthresh) {
 417                 acked = tcp_slow_start(tp, acked);
 418                 if (!acked)
 419                         return;
 420         }
 421         /* In dangerous area, increase slowly. */
 422         tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 423 }
 424 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 425
 426 /* Slow start threshold is half the congestion window (min 2) */
 427 u32 tcp_reno_ssthresh(struct sock *sk)
 428 {
 429         const struct tcp_sock *tp = tcp_sk(sk);
 430
 431         return max(tp->snd_cwnd >> 1U, 2U);
 432 }
 433 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 434
 435 struct tcp_congestion_ops tcp_reno = {
 436         .flags          = TCP_CONG_NON_RESTRICTED,
 437         .name           = "reno",
 438         .owner          = THIS_MODULE,
 439         .ssthresh       = tcp_reno_ssthresh,
 440         .cong_avoid     = tcp_reno_cong_avoid,
 441 };