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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! */
24struct 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(!bpf_try_module_get(ca, 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 (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
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 bpf_module_put(icsk->icsk_ca_ops, 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 (!bpf_try_module_get(ca, ca->owner)) {
226 ret = -EBUSY;
227 } else {
228 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
229 if (prev)
230 bpf_module_put(prev, 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 if (WARN_ON_ONCE(offs >= maxlen))
261 break;
262 }
263 rcu_read_unlock();
264}
265
266/* Get current default congestion control */
267void tcp_get_default_congestion_control(struct net *net, char *name)
268{
269 const struct tcp_congestion_ops *ca;
270
271 rcu_read_lock();
272 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
273 strncpy(name, ca->name, TCP_CA_NAME_MAX);
274 rcu_read_unlock();
275}
276
277/* Built list of non-restricted congestion control values */
278void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
279{
280 struct tcp_congestion_ops *ca;
281 size_t offs = 0;
282
283 *buf = '\0';
284 rcu_read_lock();
285 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
286 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
287 continue;
288 offs += snprintf(buf + offs, maxlen - offs,
289 "%s%s",
290 offs == 0 ? "" : " ", ca->name);
291
292 if (WARN_ON_ONCE(offs >= maxlen))
293 break;
294 }
295 rcu_read_unlock();
296}
297
298/* Change list of non-restricted congestion control */
299int 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 }
330out:
331 spin_unlock(&tcp_cong_list_lock);
332 kfree(saved_clone);
333
334 return ret;
335}
336
337/* Change congestion control for socket. If load is false, then it is the
338 * responsibility of the caller to call tcp_init_congestion_control or
339 * tcp_reinit_congestion_control (if the current congestion control was
340 * already initialized.
341 */
342int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
343 bool reinit, bool cap_net_admin)
344{
345 struct inet_connection_sock *icsk = inet_csk(sk);
346 const struct tcp_congestion_ops *ca;
347 int err = 0;
348
349 if (icsk->icsk_ca_dst_locked)
350 return -EPERM;
351
352 rcu_read_lock();
353 if (!load)
354 ca = tcp_ca_find(name);
355 else
356 ca = tcp_ca_find_autoload(sock_net(sk), name);
357
358 /* No change asking for existing value */
359 if (ca == icsk->icsk_ca_ops) {
360 icsk->icsk_ca_setsockopt = 1;
361 goto out;
362 }
363
364 if (!ca) {
365 err = -ENOENT;
366 } else if (!load) {
367 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
368
369 if (bpf_try_module_get(ca, ca->owner)) {
370 if (reinit) {
371 tcp_reinit_congestion_control(sk, ca);
372 } else {
373 icsk->icsk_ca_ops = ca;
374 bpf_module_put(old_ca, old_ca->owner);
375 }
376 } else {
377 err = -EBUSY;
378 }
379 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin)) {
380 err = -EPERM;
381 } else if (!bpf_try_module_get(ca, ca->owner)) {
382 err = -EBUSY;
383 } else {
384 tcp_reinit_congestion_control(sk, ca);
385 }
386 out:
387 rcu_read_unlock();
388 return err;
389}
390
391/* Slow start is used when congestion window is no greater than the slow start
392 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
393 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
394 * something better;) a packet is only considered (s)acked in its entirety to
395 * defend the ACK attacks described in the RFC. Slow start processes a stretch
396 * ACK of degree N as if N acks of degree 1 are received back to back except
397 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
398 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
399 */
400u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
401{
402 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
403
404 acked -= cwnd - tp->snd_cwnd;
405 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
406
407 return acked;
408}
409EXPORT_SYMBOL_GPL(tcp_slow_start);
410
411/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
412 * for every packet that was ACKed.
413 */
414void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
415{
416 /* If credits accumulated at a higher w, apply them gently now. */
417 if (tp->snd_cwnd_cnt >= w) {
418 tp->snd_cwnd_cnt = 0;
419 tp->snd_cwnd++;
420 }
421
422 tp->snd_cwnd_cnt += acked;
423 if (tp->snd_cwnd_cnt >= w) {
424 u32 delta = tp->snd_cwnd_cnt / w;
425
426 tp->snd_cwnd_cnt -= delta * w;
427 tp->snd_cwnd += delta;
428 }
429 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
430}
431EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
432
433/*
434 * TCP Reno congestion control
435 * This is special case used for fallback as well.
436 */
437/* This is Jacobson's slow start and congestion avoidance.
438 * SIGCOMM '88, p. 328.
439 */
440void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
441{
442 struct tcp_sock *tp = tcp_sk(sk);
443
444 if (!tcp_is_cwnd_limited(sk))
445 return;
446
447 /* In "safe" area, increase. */
448 if (tcp_in_slow_start(tp)) {
449 acked = tcp_slow_start(tp, acked);
450 if (!acked)
451 return;
452 }
453 /* In dangerous area, increase slowly. */
454 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
455}
456EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
457
458/* Slow start threshold is half the congestion window (min 2) */
459u32 tcp_reno_ssthresh(struct sock *sk)
460{
461 const struct tcp_sock *tp = tcp_sk(sk);
462
463 return max(tp->snd_cwnd >> 1U, 2U);
464}
465EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
466
467u32 tcp_reno_undo_cwnd(struct sock *sk)
468{
469 const struct tcp_sock *tp = tcp_sk(sk);
470
471 return max(tp->snd_cwnd, tp->prior_cwnd);
472}
473EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
474
475struct tcp_congestion_ops tcp_reno = {
476 .flags = TCP_CONG_NON_RESTRICTED,
477 .name = "reno",
478 .owner = THIS_MODULE,
479 .ssthresh = tcp_reno_ssthresh,
480 .cong_avoid = tcp_reno_cong_avoid,
481 .undo_cwnd = tcp_reno_undo_cwnd,
482};
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#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 <net/tcp.h>
17
18int sysctl_tcp_max_ssthresh = 0;
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/*
37 * Attach new congestion control algorithm to the list
38 * of available options.
39 */
40int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
41{
42 int ret = 0;
43
44 /* all algorithms must implement ssthresh and cong_avoid ops */
45 if (!ca->ssthresh || !ca->cong_avoid) {
46 pr_err("%s does not implement required ops\n", ca->name);
47 return -EINVAL;
48 }
49
50 spin_lock(&tcp_cong_list_lock);
51 if (tcp_ca_find(ca->name)) {
52 pr_notice("%s already registered\n", ca->name);
53 ret = -EEXIST;
54 } else {
55 list_add_tail_rcu(&ca->list, &tcp_cong_list);
56 pr_info("%s registered\n", ca->name);
57 }
58 spin_unlock(&tcp_cong_list_lock);
59
60 return ret;
61}
62EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
63
64/*
65 * Remove congestion control algorithm, called from
66 * the module's remove function. Module ref counts are used
67 * to ensure that this can't be done till all sockets using
68 * that method are closed.
69 */
70void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
71{
72 spin_lock(&tcp_cong_list_lock);
73 list_del_rcu(&ca->list);
74 spin_unlock(&tcp_cong_list_lock);
75}
76EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
77
78/* Assign choice of congestion control. */
79void tcp_init_congestion_control(struct sock *sk)
80{
81 struct inet_connection_sock *icsk = inet_csk(sk);
82 struct tcp_congestion_ops *ca;
83
84 /* if no choice made yet assign the current value set as default */
85 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
86 rcu_read_lock();
87 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
88 if (try_module_get(ca->owner)) {
89 icsk->icsk_ca_ops = ca;
90 break;
91 }
92
93 /* fallback to next available */
94 }
95 rcu_read_unlock();
96 }
97
98 if (icsk->icsk_ca_ops->init)
99 icsk->icsk_ca_ops->init(sk);
100}
101
102/* Manage refcounts on socket close. */
103void tcp_cleanup_congestion_control(struct sock *sk)
104{
105 struct inet_connection_sock *icsk = inet_csk(sk);
106
107 if (icsk->icsk_ca_ops->release)
108 icsk->icsk_ca_ops->release(sk);
109 module_put(icsk->icsk_ca_ops->owner);
110}
111
112/* Used by sysctl to change default congestion control */
113int tcp_set_default_congestion_control(const char *name)
114{
115 struct tcp_congestion_ops *ca;
116 int ret = -ENOENT;
117
118 spin_lock(&tcp_cong_list_lock);
119 ca = tcp_ca_find(name);
120#ifdef CONFIG_MODULES
121 if (!ca && capable(CAP_NET_ADMIN)) {
122 spin_unlock(&tcp_cong_list_lock);
123
124 request_module("tcp_%s", name);
125 spin_lock(&tcp_cong_list_lock);
126 ca = tcp_ca_find(name);
127 }
128#endif
129
130 if (ca) {
131 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
132 list_move(&ca->list, &tcp_cong_list);
133 ret = 0;
134 }
135 spin_unlock(&tcp_cong_list_lock);
136
137 return ret;
138}
139
140/* Set default value from kernel configuration at bootup */
141static int __init tcp_congestion_default(void)
142{
143 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
144}
145late_initcall(tcp_congestion_default);
146
147
148/* Build string with list of available congestion control values */
149void tcp_get_available_congestion_control(char *buf, size_t maxlen)
150{
151 struct tcp_congestion_ops *ca;
152 size_t offs = 0;
153
154 rcu_read_lock();
155 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
156 offs += snprintf(buf + offs, maxlen - offs,
157 "%s%s",
158 offs == 0 ? "" : " ", ca->name);
159
160 }
161 rcu_read_unlock();
162}
163
164/* Get current default congestion control */
165void tcp_get_default_congestion_control(char *name)
166{
167 struct tcp_congestion_ops *ca;
168 /* We will always have reno... */
169 BUG_ON(list_empty(&tcp_cong_list));
170
171 rcu_read_lock();
172 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
173 strncpy(name, ca->name, TCP_CA_NAME_MAX);
174 rcu_read_unlock();
175}
176
177/* Built list of non-restricted congestion control values */
178void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
179{
180 struct tcp_congestion_ops *ca;
181 size_t offs = 0;
182
183 *buf = '\0';
184 rcu_read_lock();
185 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
186 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
187 continue;
188 offs += snprintf(buf + offs, maxlen - offs,
189 "%s%s",
190 offs == 0 ? "" : " ", ca->name);
191
192 }
193 rcu_read_unlock();
194}
195
196/* Change list of non-restricted congestion control */
197int tcp_set_allowed_congestion_control(char *val)
198{
199 struct tcp_congestion_ops *ca;
200 char *saved_clone, *clone, *name;
201 int ret = 0;
202
203 saved_clone = clone = kstrdup(val, GFP_USER);
204 if (!clone)
205 return -ENOMEM;
206
207 spin_lock(&tcp_cong_list_lock);
208 /* pass 1 check for bad entries */
209 while ((name = strsep(&clone, " ")) && *name) {
210 ca = tcp_ca_find(name);
211 if (!ca) {
212 ret = -ENOENT;
213 goto out;
214 }
215 }
216
217 /* pass 2 clear old values */
218 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
219 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
220
221 /* pass 3 mark as allowed */
222 while ((name = strsep(&val, " ")) && *name) {
223 ca = tcp_ca_find(name);
224 WARN_ON(!ca);
225 if (ca)
226 ca->flags |= TCP_CONG_NON_RESTRICTED;
227 }
228out:
229 spin_unlock(&tcp_cong_list_lock);
230 kfree(saved_clone);
231
232 return ret;
233}
234
235
236/* Change congestion control for socket */
237int tcp_set_congestion_control(struct sock *sk, const char *name)
238{
239 struct inet_connection_sock *icsk = inet_csk(sk);
240 struct tcp_congestion_ops *ca;
241 int err = 0;
242
243 rcu_read_lock();
244 ca = tcp_ca_find(name);
245
246 /* no change asking for existing value */
247 if (ca == icsk->icsk_ca_ops)
248 goto out;
249
250#ifdef CONFIG_MODULES
251 /* not found attempt to autoload module */
252 if (!ca && capable(CAP_NET_ADMIN)) {
253 rcu_read_unlock();
254 request_module("tcp_%s", name);
255 rcu_read_lock();
256 ca = tcp_ca_find(name);
257 }
258#endif
259 if (!ca)
260 err = -ENOENT;
261
262 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
263 err = -EPERM;
264
265 else if (!try_module_get(ca->owner))
266 err = -EBUSY;
267
268 else {
269 tcp_cleanup_congestion_control(sk);
270 icsk->icsk_ca_ops = ca;
271
272 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
273 icsk->icsk_ca_ops->init(sk);
274 }
275 out:
276 rcu_read_unlock();
277 return err;
278}
279
280/* RFC2861 Check whether we are limited by application or congestion window
281 * This is the inverse of cwnd check in tcp_tso_should_defer
282 */
283bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
284{
285 const struct tcp_sock *tp = tcp_sk(sk);
286 u32 left;
287
288 if (in_flight >= tp->snd_cwnd)
289 return true;
290
291 left = tp->snd_cwnd - in_flight;
292 if (sk_can_gso(sk) &&
293 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
294 left * tp->mss_cache < sk->sk_gso_max_size &&
295 left < sk->sk_gso_max_segs)
296 return true;
297 return left <= tcp_max_tso_deferred_mss(tp);
298}
299EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
300
301/*
302 * Slow start is used when congestion window is less than slow start
303 * threshold. This version implements the basic RFC2581 version
304 * and optionally supports:
305 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
306 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
307 */
308void tcp_slow_start(struct tcp_sock *tp)
309{
310 int cnt; /* increase in packets */
311
312 /* RFC3465: ABC Slow start
313 * Increase only after a full MSS of bytes is acked
314 *
315 * TCP sender SHOULD increase cwnd by the number of
316 * previously unacknowledged bytes ACKed by each incoming
317 * acknowledgment, provided the increase is not more than L
318 */
319 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
320 return;
321
322 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
323 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
324 else
325 cnt = tp->snd_cwnd; /* exponential increase */
326
327 /* RFC3465: ABC
328 * We MAY increase by 2 if discovered delayed ack
329 */
330 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
331 cnt <<= 1;
332 tp->bytes_acked = 0;
333
334 tp->snd_cwnd_cnt += cnt;
335 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
336 tp->snd_cwnd_cnt -= tp->snd_cwnd;
337 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
338 tp->snd_cwnd++;
339 }
340}
341EXPORT_SYMBOL_GPL(tcp_slow_start);
342
343/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
344void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
345{
346 if (tp->snd_cwnd_cnt >= w) {
347 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
348 tp->snd_cwnd++;
349 tp->snd_cwnd_cnt = 0;
350 } else {
351 tp->snd_cwnd_cnt++;
352 }
353}
354EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
355
356/*
357 * TCP Reno congestion control
358 * This is special case used for fallback as well.
359 */
360/* This is Jacobson's slow start and congestion avoidance.
361 * SIGCOMM '88, p. 328.
362 */
363void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
364{
365 struct tcp_sock *tp = tcp_sk(sk);
366
367 if (!tcp_is_cwnd_limited(sk, in_flight))
368 return;
369
370 /* In "safe" area, increase. */
371 if (tp->snd_cwnd <= tp->snd_ssthresh)
372 tcp_slow_start(tp);
373
374 /* In dangerous area, increase slowly. */
375 else if (sysctl_tcp_abc) {
376 /* RFC3465: Appropriate Byte Count
377 * increase once for each full cwnd acked
378 */
379 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
380 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
381 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
382 tp->snd_cwnd++;
383 }
384 } else {
385 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
386 }
387}
388EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
389
390/* Slow start threshold is half the congestion window (min 2) */
391u32 tcp_reno_ssthresh(struct sock *sk)
392{
393 const struct tcp_sock *tp = tcp_sk(sk);
394 return max(tp->snd_cwnd >> 1U, 2U);
395}
396EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
397
398/* Lower bound on congestion window with halving. */
399u32 tcp_reno_min_cwnd(const struct sock *sk)
400{
401 const struct tcp_sock *tp = tcp_sk(sk);
402 return tp->snd_ssthresh/2;
403}
404EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
405
406struct tcp_congestion_ops tcp_reno = {
407 .flags = TCP_CONG_NON_RESTRICTED,
408 .name = "reno",
409 .owner = THIS_MODULE,
410 .ssthresh = tcp_reno_ssthresh,
411 .cong_avoid = tcp_reno_cong_avoid,
412 .min_cwnd = tcp_reno_min_cwnd,
413};
414
415/* Initial congestion control used (until SYN)
416 * really reno under another name so we can tell difference
417 * during tcp_set_default_congestion_control
418 */
419struct tcp_congestion_ops tcp_init_congestion_ops = {
420 .name = "",
421 .owner = THIS_MODULE,
422 .ssthresh = tcp_reno_ssthresh,
423 .cong_avoid = tcp_reno_cong_avoid,
424 .min_cwnd = tcp_reno_min_cwnd,
425};
426EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);