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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
20static DEFINE_SPINLOCK(tcp_cong_list_lock);
21static LIST_HEAD(tcp_cong_list);
22
23/* Simple linear search, don't expect many entries! */
24static 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 */
37static 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. */
54struct 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 */
70int 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}
96EXPORT_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 */
104void 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}
119EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
120
121u32 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}
138EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
139
140char *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}
154EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
155
156/* Assign choice of congestion control. */
157void 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
177void 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
190static 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. */
205void 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 */
215int 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 */
241static int __init tcp_congestion_default(void)
242{
243 return tcp_set_default_congestion_control(&init_net,
244 CONFIG_DEFAULT_TCP_CONG);
245}
246late_initcall(tcp_congestion_default);
247
248/* Build string with list of available congestion control values */
249void 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 */
264void 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 */
275void 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 */
293int 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 }
324out:
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 */
336int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
337 bool reinit, bool cap_net_admin)
338{
339 struct inet_connection_sock *icsk = inet_csk(sk);
340 const struct tcp_congestion_ops *ca;
341 int err = 0;
342
343 if (icsk->icsk_ca_dst_locked)
344 return -EPERM;
345
346 rcu_read_lock();
347 if (!load)
348 ca = tcp_ca_find(name);
349 else
350 ca = tcp_ca_find_autoload(sock_net(sk), name);
351
352 /* No change asking for existing value */
353 if (ca == icsk->icsk_ca_ops) {
354 icsk->icsk_ca_setsockopt = 1;
355 goto out;
356 }
357
358 if (!ca) {
359 err = -ENOENT;
360 } else if (!load) {
361 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
362
363 if (try_module_get(ca->owner)) {
364 if (reinit) {
365 tcp_reinit_congestion_control(sk, ca);
366 } else {
367 icsk->icsk_ca_ops = ca;
368 module_put(old_ca->owner);
369 }
370 } else {
371 err = -EBUSY;
372 }
373 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || 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 */
394u32 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}
403EXPORT_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 */
408void 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}
425EXPORT_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 */
434void 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}
450EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
451
452/* Slow start threshold is half the congestion window (min 2) */
453u32 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}
459EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
460
461u32 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}
467EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
468
469struct 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};
1/*
2 * Plugable TCP congestion control support and newReno
3 * congestion control.
4 * Based on ideas from I/O scheduler suport and Web100.
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
9#include <linux/module.h>
10#include <linux/mm.h>
11#include <linux/types.h>
12#include <linux/list.h>
13#include <linux/gfp.h>
14#include <net/tcp.h>
15
16int sysctl_tcp_max_ssthresh = 0;
17
18static DEFINE_SPINLOCK(tcp_cong_list_lock);
19static LIST_HEAD(tcp_cong_list);
20
21/* Simple linear search, don't expect many entries! */
22static struct tcp_congestion_ops *tcp_ca_find(const char *name)
23{
24 struct tcp_congestion_ops *e;
25
26 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
27 if (strcmp(e->name, name) == 0)
28 return e;
29 }
30
31 return NULL;
32}
33
34/*
35 * Attach new congestion control algorithm to the list
36 * of available options.
37 */
38int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
39{
40 int ret = 0;
41
42 /* all algorithms must implement ssthresh and cong_avoid ops */
43 if (!ca->ssthresh || !ca->cong_avoid) {
44 printk(KERN_ERR "TCP %s does not implement required ops\n",
45 ca->name);
46 return -EINVAL;
47 }
48
49 spin_lock(&tcp_cong_list_lock);
50 if (tcp_ca_find(ca->name)) {
51 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
52 ret = -EEXIST;
53 } else {
54 list_add_tail_rcu(&ca->list, &tcp_cong_list);
55 printk(KERN_INFO "TCP %s registered\n", ca->name);
56 }
57 spin_unlock(&tcp_cong_list_lock);
58
59 return ret;
60}
61EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
62
63/*
64 * Remove congestion control algorithm, called from
65 * the module's remove function. Module ref counts are used
66 * to ensure that this can't be done till all sockets using
67 * that method are closed.
68 */
69void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
70{
71 spin_lock(&tcp_cong_list_lock);
72 list_del_rcu(&ca->list);
73 spin_unlock(&tcp_cong_list_lock);
74}
75EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
76
77/* Assign choice of congestion control. */
78void tcp_init_congestion_control(struct sock *sk)
79{
80 struct inet_connection_sock *icsk = inet_csk(sk);
81 struct tcp_congestion_ops *ca;
82
83 /* if no choice made yet assign the current value set as default */
84 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
85 rcu_read_lock();
86 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
87 if (try_module_get(ca->owner)) {
88 icsk->icsk_ca_ops = ca;
89 break;
90 }
91
92 /* fallback to next available */
93 }
94 rcu_read_unlock();
95 }
96
97 if (icsk->icsk_ca_ops->init)
98 icsk->icsk_ca_ops->init(sk);
99}
100
101/* Manage refcounts on socket close. */
102void tcp_cleanup_congestion_control(struct sock *sk)
103{
104 struct inet_connection_sock *icsk = inet_csk(sk);
105
106 if (icsk->icsk_ca_ops->release)
107 icsk->icsk_ca_ops->release(sk);
108 module_put(icsk->icsk_ca_ops->owner);
109}
110
111/* Used by sysctl to change default congestion control */
112int tcp_set_default_congestion_control(const char *name)
113{
114 struct tcp_congestion_ops *ca;
115 int ret = -ENOENT;
116
117 spin_lock(&tcp_cong_list_lock);
118 ca = tcp_ca_find(name);
119#ifdef CONFIG_MODULES
120 if (!ca && capable(CAP_NET_ADMIN)) {
121 spin_unlock(&tcp_cong_list_lock);
122
123 request_module("tcp_%s", name);
124 spin_lock(&tcp_cong_list_lock);
125 ca = tcp_ca_find(name);
126 }
127#endif
128
129 if (ca) {
130 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
131 list_move(&ca->list, &tcp_cong_list);
132 ret = 0;
133 }
134 spin_unlock(&tcp_cong_list_lock);
135
136 return ret;
137}
138
139/* Set default value from kernel configuration at bootup */
140static int __init tcp_congestion_default(void)
141{
142 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
143}
144late_initcall(tcp_congestion_default);
145
146
147/* Build string with list of available congestion control values */
148void tcp_get_available_congestion_control(char *buf, size_t maxlen)
149{
150 struct tcp_congestion_ops *ca;
151 size_t offs = 0;
152
153 rcu_read_lock();
154 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
155 offs += snprintf(buf + offs, maxlen - offs,
156 "%s%s",
157 offs == 0 ? "" : " ", ca->name);
158
159 }
160 rcu_read_unlock();
161}
162
163/* Get current default congestion control */
164void tcp_get_default_congestion_control(char *name)
165{
166 struct tcp_congestion_ops *ca;
167 /* We will always have reno... */
168 BUG_ON(list_empty(&tcp_cong_list));
169
170 rcu_read_lock();
171 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
172 strncpy(name, ca->name, TCP_CA_NAME_MAX);
173 rcu_read_unlock();
174}
175
176/* Built list of non-restricted congestion control values */
177void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
178{
179 struct tcp_congestion_ops *ca;
180 size_t offs = 0;
181
182 *buf = '\0';
183 rcu_read_lock();
184 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
185 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
186 continue;
187 offs += snprintf(buf + offs, maxlen - offs,
188 "%s%s",
189 offs == 0 ? "" : " ", ca->name);
190
191 }
192 rcu_read_unlock();
193}
194
195/* Change list of non-restricted congestion control */
196int tcp_set_allowed_congestion_control(char *val)
197{
198 struct tcp_congestion_ops *ca;
199 char *saved_clone, *clone, *name;
200 int ret = 0;
201
202 saved_clone = clone = kstrdup(val, GFP_USER);
203 if (!clone)
204 return -ENOMEM;
205
206 spin_lock(&tcp_cong_list_lock);
207 /* pass 1 check for bad entries */
208 while ((name = strsep(&clone, " ")) && *name) {
209 ca = tcp_ca_find(name);
210 if (!ca) {
211 ret = -ENOENT;
212 goto out;
213 }
214 }
215
216 /* pass 2 clear old values */
217 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
218 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
219
220 /* pass 3 mark as allowed */
221 while ((name = strsep(&val, " ")) && *name) {
222 ca = tcp_ca_find(name);
223 WARN_ON(!ca);
224 if (ca)
225 ca->flags |= TCP_CONG_NON_RESTRICTED;
226 }
227out:
228 spin_unlock(&tcp_cong_list_lock);
229 kfree(saved_clone);
230
231 return ret;
232}
233
234
235/* Change congestion control for socket */
236int tcp_set_congestion_control(struct sock *sk, const char *name)
237{
238 struct inet_connection_sock *icsk = inet_csk(sk);
239 struct tcp_congestion_ops *ca;
240 int err = 0;
241
242 rcu_read_lock();
243 ca = tcp_ca_find(name);
244
245 /* no change asking for existing value */
246 if (ca == icsk->icsk_ca_ops)
247 goto out;
248
249#ifdef CONFIG_MODULES
250 /* not found attempt to autoload module */
251 if (!ca && capable(CAP_NET_ADMIN)) {
252 rcu_read_unlock();
253 request_module("tcp_%s", name);
254 rcu_read_lock();
255 ca = tcp_ca_find(name);
256 }
257#endif
258 if (!ca)
259 err = -ENOENT;
260
261 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
262 err = -EPERM;
263
264 else if (!try_module_get(ca->owner))
265 err = -EBUSY;
266
267 else {
268 tcp_cleanup_congestion_control(sk);
269 icsk->icsk_ca_ops = ca;
270
271 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
272 icsk->icsk_ca_ops->init(sk);
273 }
274 out:
275 rcu_read_unlock();
276 return err;
277}
278
279/* RFC2861 Check whether we are limited by application or congestion window
280 * This is the inverse of cwnd check in tcp_tso_should_defer
281 */
282int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
283{
284 const struct tcp_sock *tp = tcp_sk(sk);
285 u32 left;
286
287 if (in_flight >= tp->snd_cwnd)
288 return 1;
289
290 left = tp->snd_cwnd - in_flight;
291 if (sk_can_gso(sk) &&
292 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
293 left * tp->mss_cache < sk->sk_gso_max_size)
294 return 1;
295 return left <= tcp_max_burst(tp);
296}
297EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
298
299/*
300 * Slow start is used when congestion window is less than slow start
301 * threshold. This version implements the basic RFC2581 version
302 * and optionally supports:
303 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
304 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
305 */
306void tcp_slow_start(struct tcp_sock *tp)
307{
308 int cnt; /* increase in packets */
309
310 /* RFC3465: ABC Slow start
311 * Increase only after a full MSS of bytes is acked
312 *
313 * TCP sender SHOULD increase cwnd by the number of
314 * previously unacknowledged bytes ACKed by each incoming
315 * acknowledgment, provided the increase is not more than L
316 */
317 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
318 return;
319
320 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
321 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
322 else
323 cnt = tp->snd_cwnd; /* exponential increase */
324
325 /* RFC3465: ABC
326 * We MAY increase by 2 if discovered delayed ack
327 */
328 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
329 cnt <<= 1;
330 tp->bytes_acked = 0;
331
332 tp->snd_cwnd_cnt += cnt;
333 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
334 tp->snd_cwnd_cnt -= tp->snd_cwnd;
335 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
336 tp->snd_cwnd++;
337 }
338}
339EXPORT_SYMBOL_GPL(tcp_slow_start);
340
341/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
342void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
343{
344 if (tp->snd_cwnd_cnt >= w) {
345 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
346 tp->snd_cwnd++;
347 tp->snd_cwnd_cnt = 0;
348 } else {
349 tp->snd_cwnd_cnt++;
350 }
351}
352EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
353
354/*
355 * TCP Reno congestion control
356 * This is special case used for fallback as well.
357 */
358/* This is Jacobson's slow start and congestion avoidance.
359 * SIGCOMM '88, p. 328.
360 */
361void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
362{
363 struct tcp_sock *tp = tcp_sk(sk);
364
365 if (!tcp_is_cwnd_limited(sk, in_flight))
366 return;
367
368 /* In "safe" area, increase. */
369 if (tp->snd_cwnd <= tp->snd_ssthresh)
370 tcp_slow_start(tp);
371
372 /* In dangerous area, increase slowly. */
373 else if (sysctl_tcp_abc) {
374 /* RFC3465: Appropriate Byte Count
375 * increase once for each full cwnd acked
376 */
377 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
378 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
379 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
380 tp->snd_cwnd++;
381 }
382 } else {
383 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
384 }
385}
386EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
387
388/* Slow start threshold is half the congestion window (min 2) */
389u32 tcp_reno_ssthresh(struct sock *sk)
390{
391 const struct tcp_sock *tp = tcp_sk(sk);
392 return max(tp->snd_cwnd >> 1U, 2U);
393}
394EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
395
396/* Lower bound on congestion window with halving. */
397u32 tcp_reno_min_cwnd(const struct sock *sk)
398{
399 const struct tcp_sock *tp = tcp_sk(sk);
400 return tp->snd_ssthresh/2;
401}
402EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
403
404struct tcp_congestion_ops tcp_reno = {
405 .flags = TCP_CONG_NON_RESTRICTED,
406 .name = "reno",
407 .owner = THIS_MODULE,
408 .ssthresh = tcp_reno_ssthresh,
409 .cong_avoid = tcp_reno_cong_avoid,
410 .min_cwnd = tcp_reno_min_cwnd,
411};
412
413/* Initial congestion control used (until SYN)
414 * really reno under another name so we can tell difference
415 * during tcp_set_default_congestion_control
416 */
417struct tcp_congestion_ops tcp_init_congestion_ops = {
418 .name = "",
419 .owner = THIS_MODULE,
420 .ssthresh = tcp_reno_ssthresh,
421 .cong_avoid = tcp_reno_cong_avoid,
422 .min_cwnd = tcp_reno_min_cwnd,
423};
424EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);