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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);
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#include <trace/events/tcp.h>
20
21static DEFINE_SPINLOCK(tcp_cong_list_lock);
22static LIST_HEAD(tcp_cong_list);
23
24/* Simple linear search, don't expect many entries! */
25struct tcp_congestion_ops *tcp_ca_find(const char *name)
26{
27 struct tcp_congestion_ops *e;
28
29 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
30 if (strcmp(e->name, name) == 0)
31 return e;
32 }
33
34 return NULL;
35}
36
37void tcp_set_ca_state(struct sock *sk, const u8 ca_state)
38{
39 struct inet_connection_sock *icsk = inet_csk(sk);
40
41 trace_tcp_cong_state_set(sk, ca_state);
42
43 if (icsk->icsk_ca_ops->set_state)
44 icsk->icsk_ca_ops->set_state(sk, ca_state);
45 icsk->icsk_ca_state = ca_state;
46}
47
48/* Must be called with rcu lock held */
49static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
50 const char *name)
51{
52 struct tcp_congestion_ops *ca = tcp_ca_find(name);
53
54#ifdef CONFIG_MODULES
55 if (!ca && capable(CAP_NET_ADMIN)) {
56 rcu_read_unlock();
57 request_module("tcp_%s", name);
58 rcu_read_lock();
59 ca = tcp_ca_find(name);
60 }
61#endif
62 return ca;
63}
64
65/* Simple linear search, not much in here. */
66struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
67{
68 struct tcp_congestion_ops *e;
69
70 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
71 if (e->key == key)
72 return e;
73 }
74
75 return NULL;
76}
77
78/*
79 * Attach new congestion control algorithm to the list
80 * of available options.
81 */
82int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
83{
84 int ret = 0;
85
86 /* all algorithms must implement these */
87 if (!ca->ssthresh || !ca->undo_cwnd ||
88 !(ca->cong_avoid || ca->cong_control)) {
89 pr_err("%s does not implement required ops\n", ca->name);
90 return -EINVAL;
91 }
92
93 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
94
95 spin_lock(&tcp_cong_list_lock);
96 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
97 pr_notice("%s already registered or non-unique key\n",
98 ca->name);
99 ret = -EEXIST;
100 } else {
101 list_add_tail_rcu(&ca->list, &tcp_cong_list);
102 pr_debug("%s registered\n", ca->name);
103 }
104 spin_unlock(&tcp_cong_list_lock);
105
106 return ret;
107}
108EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
109
110/*
111 * Remove congestion control algorithm, called from
112 * the module's remove function. Module ref counts are used
113 * to ensure that this can't be done till all sockets using
114 * that method are closed.
115 */
116void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
117{
118 spin_lock(&tcp_cong_list_lock);
119 list_del_rcu(&ca->list);
120 spin_unlock(&tcp_cong_list_lock);
121
122 /* Wait for outstanding readers to complete before the
123 * module gets removed entirely.
124 *
125 * A try_module_get() should fail by now as our module is
126 * in "going" state since no refs are held anymore and
127 * module_exit() handler being called.
128 */
129 synchronize_rcu();
130}
131EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
132
133u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
134{
135 const struct tcp_congestion_ops *ca;
136 u32 key = TCP_CA_UNSPEC;
137
138 might_sleep();
139
140 rcu_read_lock();
141 ca = tcp_ca_find_autoload(net, name);
142 if (ca) {
143 key = ca->key;
144 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
145 }
146 rcu_read_unlock();
147
148 return key;
149}
150
151char *tcp_ca_get_name_by_key(u32 key, char *buffer)
152{
153 const struct tcp_congestion_ops *ca;
154 char *ret = NULL;
155
156 rcu_read_lock();
157 ca = tcp_ca_find_key(key);
158 if (ca)
159 ret = strncpy(buffer, ca->name,
160 TCP_CA_NAME_MAX);
161 rcu_read_unlock();
162
163 return ret;
164}
165
166/* Assign choice of congestion control. */
167void tcp_assign_congestion_control(struct sock *sk)
168{
169 struct net *net = sock_net(sk);
170 struct inet_connection_sock *icsk = inet_csk(sk);
171 const struct tcp_congestion_ops *ca;
172
173 rcu_read_lock();
174 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
175 if (unlikely(!bpf_try_module_get(ca, ca->owner)))
176 ca = &tcp_reno;
177 icsk->icsk_ca_ops = ca;
178 rcu_read_unlock();
179
180 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
181 if (ca->flags & TCP_CONG_NEEDS_ECN)
182 INET_ECN_xmit(sk);
183 else
184 INET_ECN_dontxmit(sk);
185}
186
187void tcp_init_congestion_control(struct sock *sk)
188{
189 struct inet_connection_sock *icsk = inet_csk(sk);
190
191 tcp_sk(sk)->prior_ssthresh = 0;
192 if (icsk->icsk_ca_ops->init)
193 icsk->icsk_ca_ops->init(sk);
194 if (tcp_ca_needs_ecn(sk))
195 INET_ECN_xmit(sk);
196 else
197 INET_ECN_dontxmit(sk);
198 icsk->icsk_ca_initialized = 1;
199}
200
201static void tcp_reinit_congestion_control(struct sock *sk,
202 const struct tcp_congestion_ops *ca)
203{
204 struct inet_connection_sock *icsk = inet_csk(sk);
205
206 tcp_cleanup_congestion_control(sk);
207 icsk->icsk_ca_ops = ca;
208 icsk->icsk_ca_setsockopt = 1;
209 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
210
211 if (ca->flags & TCP_CONG_NEEDS_ECN)
212 INET_ECN_xmit(sk);
213 else
214 INET_ECN_dontxmit(sk);
215
216 if (!((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
217 tcp_init_congestion_control(sk);
218}
219
220/* Manage refcounts on socket close. */
221void tcp_cleanup_congestion_control(struct sock *sk)
222{
223 struct inet_connection_sock *icsk = inet_csk(sk);
224
225 if (icsk->icsk_ca_ops->release)
226 icsk->icsk_ca_ops->release(sk);
227 bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner);
228}
229
230/* Used by sysctl to change default congestion control */
231int tcp_set_default_congestion_control(struct net *net, const char *name)
232{
233 struct tcp_congestion_ops *ca;
234 const struct tcp_congestion_ops *prev;
235 int ret;
236
237 rcu_read_lock();
238 ca = tcp_ca_find_autoload(net, name);
239 if (!ca) {
240 ret = -ENOENT;
241 } else if (!bpf_try_module_get(ca, ca->owner)) {
242 ret = -EBUSY;
243 } else if (!net_eq(net, &init_net) &&
244 !(ca->flags & TCP_CONG_NON_RESTRICTED)) {
245 /* Only init netns can set default to a restricted algorithm */
246 ret = -EPERM;
247 } else {
248 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
249 if (prev)
250 bpf_module_put(prev, prev->owner);
251
252 ca->flags |= TCP_CONG_NON_RESTRICTED;
253 ret = 0;
254 }
255 rcu_read_unlock();
256
257 return ret;
258}
259
260/* Set default value from kernel configuration at bootup */
261static int __init tcp_congestion_default(void)
262{
263 return tcp_set_default_congestion_control(&init_net,
264 CONFIG_DEFAULT_TCP_CONG);
265}
266late_initcall(tcp_congestion_default);
267
268/* Build string with list of available congestion control values */
269void tcp_get_available_congestion_control(char *buf, size_t maxlen)
270{
271 struct tcp_congestion_ops *ca;
272 size_t offs = 0;
273
274 rcu_read_lock();
275 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
276 offs += snprintf(buf + offs, maxlen - offs,
277 "%s%s",
278 offs == 0 ? "" : " ", ca->name);
279
280 if (WARN_ON_ONCE(offs >= maxlen))
281 break;
282 }
283 rcu_read_unlock();
284}
285
286/* Get current default congestion control */
287void tcp_get_default_congestion_control(struct net *net, char *name)
288{
289 const struct tcp_congestion_ops *ca;
290
291 rcu_read_lock();
292 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
293 strncpy(name, ca->name, TCP_CA_NAME_MAX);
294 rcu_read_unlock();
295}
296
297/* Built list of non-restricted congestion control values */
298void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
299{
300 struct tcp_congestion_ops *ca;
301 size_t offs = 0;
302
303 *buf = '\0';
304 rcu_read_lock();
305 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
306 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
307 continue;
308 offs += snprintf(buf + offs, maxlen - offs,
309 "%s%s",
310 offs == 0 ? "" : " ", ca->name);
311
312 if (WARN_ON_ONCE(offs >= maxlen))
313 break;
314 }
315 rcu_read_unlock();
316}
317
318/* Change list of non-restricted congestion control */
319int tcp_set_allowed_congestion_control(char *val)
320{
321 struct tcp_congestion_ops *ca;
322 char *saved_clone, *clone, *name;
323 int ret = 0;
324
325 saved_clone = clone = kstrdup(val, GFP_USER);
326 if (!clone)
327 return -ENOMEM;
328
329 spin_lock(&tcp_cong_list_lock);
330 /* pass 1 check for bad entries */
331 while ((name = strsep(&clone, " ")) && *name) {
332 ca = tcp_ca_find(name);
333 if (!ca) {
334 ret = -ENOENT;
335 goto out;
336 }
337 }
338
339 /* pass 2 clear old values */
340 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
341 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
342
343 /* pass 3 mark as allowed */
344 while ((name = strsep(&val, " ")) && *name) {
345 ca = tcp_ca_find(name);
346 WARN_ON(!ca);
347 if (ca)
348 ca->flags |= TCP_CONG_NON_RESTRICTED;
349 }
350out:
351 spin_unlock(&tcp_cong_list_lock);
352 kfree(saved_clone);
353
354 return ret;
355}
356
357/* Change congestion control for socket. If load is false, then it is the
358 * responsibility of the caller to call tcp_init_congestion_control or
359 * tcp_reinit_congestion_control (if the current congestion control was
360 * already initialized.
361 */
362int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
363 bool cap_net_admin)
364{
365 struct inet_connection_sock *icsk = inet_csk(sk);
366 const struct tcp_congestion_ops *ca;
367 int err = 0;
368
369 if (icsk->icsk_ca_dst_locked)
370 return -EPERM;
371
372 rcu_read_lock();
373 if (!load)
374 ca = tcp_ca_find(name);
375 else
376 ca = tcp_ca_find_autoload(sock_net(sk), name);
377
378 /* No change asking for existing value */
379 if (ca == icsk->icsk_ca_ops) {
380 icsk->icsk_ca_setsockopt = 1;
381 goto out;
382 }
383
384 if (!ca)
385 err = -ENOENT;
386 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin))
387 err = -EPERM;
388 else if (!bpf_try_module_get(ca, ca->owner))
389 err = -EBUSY;
390 else
391 tcp_reinit_congestion_control(sk, ca);
392 out:
393 rcu_read_unlock();
394 return err;
395}
396
397/* Slow start is used when congestion window is no greater than the slow start
398 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
399 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
400 * something better;) a packet is only considered (s)acked in its entirety to
401 * defend the ACK attacks described in the RFC. Slow start processes a stretch
402 * ACK of degree N as if N acks of degree 1 are received back to back except
403 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
404 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
405 */
406u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
407{
408 u32 cwnd = min(tcp_snd_cwnd(tp) + acked, tp->snd_ssthresh);
409
410 acked -= cwnd - tcp_snd_cwnd(tp);
411 tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));
412
413 return acked;
414}
415EXPORT_SYMBOL_GPL(tcp_slow_start);
416
417/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
418 * for every packet that was ACKed.
419 */
420void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
421{
422 /* If credits accumulated at a higher w, apply them gently now. */
423 if (tp->snd_cwnd_cnt >= w) {
424 tp->snd_cwnd_cnt = 0;
425 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
426 }
427
428 tp->snd_cwnd_cnt += acked;
429 if (tp->snd_cwnd_cnt >= w) {
430 u32 delta = tp->snd_cwnd_cnt / w;
431
432 tp->snd_cwnd_cnt -= delta * w;
433 tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + delta);
434 }
435 tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
436}
437EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
438
439/*
440 * TCP Reno congestion control
441 * This is special case used for fallback as well.
442 */
443/* This is Jacobson's slow start and congestion avoidance.
444 * SIGCOMM '88, p. 328.
445 */
446void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
447{
448 struct tcp_sock *tp = tcp_sk(sk);
449
450 if (!tcp_is_cwnd_limited(sk))
451 return;
452
453 /* In "safe" area, increase. */
454 if (tcp_in_slow_start(tp)) {
455 acked = tcp_slow_start(tp, acked);
456 if (!acked)
457 return;
458 }
459 /* In dangerous area, increase slowly. */
460 tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
461}
462EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
463
464/* Slow start threshold is half the congestion window (min 2) */
465u32 tcp_reno_ssthresh(struct sock *sk)
466{
467 const struct tcp_sock *tp = tcp_sk(sk);
468
469 return max(tcp_snd_cwnd(tp) >> 1U, 2U);
470}
471EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
472
473u32 tcp_reno_undo_cwnd(struct sock *sk)
474{
475 const struct tcp_sock *tp = tcp_sk(sk);
476
477 return max(tcp_snd_cwnd(tp), tp->prior_cwnd);
478}
479EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
480
481struct tcp_congestion_ops tcp_reno = {
482 .flags = TCP_CONG_NON_RESTRICTED,
483 .name = "reno",
484 .owner = THIS_MODULE,
485 .ssthresh = tcp_reno_ssthresh,
486 .cong_avoid = tcp_reno_cong_avoid,
487 .undo_cwnd = tcp_reno_undo_cwnd,
488};