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317a76f9 1/*
b92022f3 2 * Pluggable TCP congestion control support and newReno
317a76f9 3 * congestion control.
02582e9b 4 * Based on ideas from I/O scheduler support and Web100.
317a76f9
SH
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
afd46503
JP
9#define pr_fmt(fmt) "TCP: " fmt
10
317a76f9
SH
11#include <linux/module.h>
12#include <linux/mm.h>
13#include <linux/types.h>
14#include <linux/list.h>
5a0e3ad6 15#include <linux/gfp.h>
317a76f9
SH
16#include <net/tcp.h>
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
5f8ef48d 26 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
317a76f9
SH
27 if (strcmp(e->name, name) == 0)
28 return e;
29 }
30
31 return NULL;
32}
33
34/*
d08df601 35 * Attach new congestion control algorithm to the list
317a76f9
SH
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 */
72dc5b92 43 if (!ca->ssthresh || !ca->cong_avoid) {
afd46503 44 pr_err("%s does not implement required ops\n", ca->name);
317a76f9
SH
45 return -EINVAL;
46 }
47
48 spin_lock(&tcp_cong_list_lock);
49 if (tcp_ca_find(ca->name)) {
afd46503 50 pr_notice("%s already registered\n", ca->name);
317a76f9
SH
51 ret = -EEXIST;
52 } else {
3d2573f7 53 list_add_tail_rcu(&ca->list, &tcp_cong_list);
afd46503 54 pr_info("%s registered\n", ca->name);
317a76f9
SH
55 }
56 spin_unlock(&tcp_cong_list_lock);
57
58 return ret;
59}
60EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
61
62/*
63 * Remove congestion control algorithm, called from
64 * the module's remove function. Module ref counts are used
65 * to ensure that this can't be done till all sockets using
66 * that method are closed.
67 */
68void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
69{
70 spin_lock(&tcp_cong_list_lock);
71 list_del_rcu(&ca->list);
72 spin_unlock(&tcp_cong_list_lock);
73}
74EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
75
76/* Assign choice of congestion control. */
55d8694f 77void tcp_assign_congestion_control(struct sock *sk)
317a76f9 78{
6687e988 79 struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9
SH
80 struct tcp_congestion_ops *ca;
81
55d8694f
FW
82 rcu_read_lock();
83 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
84 if (likely(try_module_get(ca->owner))) {
85 icsk->icsk_ca_ops = ca;
86 goto out;
317a76f9 87 }
55d8694f
FW
88 /* Fallback to next available. The last really
89 * guaranteed fallback is Reno from this list.
90 */
317a76f9 91 }
55d8694f
FW
92out:
93 rcu_read_unlock();
94
95 /* Clear out private data before diag gets it and
96 * the ca has not been initialized.
97 */
98 if (ca->get_info)
99 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
100}
101
102void tcp_init_congestion_control(struct sock *sk)
103{
104 const struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9 105
6687e988
ACM
106 if (icsk->icsk_ca_ops->init)
107 icsk->icsk_ca_ops->init(sk);
317a76f9
SH
108}
109
110/* Manage refcounts on socket close. */
6687e988 111void tcp_cleanup_congestion_control(struct sock *sk)
317a76f9 112{
6687e988
ACM
113 struct inet_connection_sock *icsk = inet_csk(sk);
114
115 if (icsk->icsk_ca_ops->release)
116 icsk->icsk_ca_ops->release(sk);
117 module_put(icsk->icsk_ca_ops->owner);
317a76f9
SH
118}
119
120/* Used by sysctl to change default congestion control */
121int tcp_set_default_congestion_control(const char *name)
122{
123 struct tcp_congestion_ops *ca;
124 int ret = -ENOENT;
125
126 spin_lock(&tcp_cong_list_lock);
127 ca = tcp_ca_find(name);
95a5afca 128#ifdef CONFIG_MODULES
a8f80e8f 129 if (!ca && capable(CAP_NET_ADMIN)) {
317a76f9
SH
130 spin_unlock(&tcp_cong_list_lock);
131
132 request_module("tcp_%s", name);
133 spin_lock(&tcp_cong_list_lock);
134 ca = tcp_ca_find(name);
135 }
136#endif
137
138 if (ca) {
164891aa 139 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
317a76f9
SH
140 list_move(&ca->list, &tcp_cong_list);
141 ret = 0;
142 }
143 spin_unlock(&tcp_cong_list_lock);
144
145 return ret;
146}
147
b1736a71
SH
148/* Set default value from kernel configuration at bootup */
149static int __init tcp_congestion_default(void)
150{
151 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
152}
153late_initcall(tcp_congestion_default);
154
3ff825b2
SH
155/* Build string with list of available congestion control values */
156void tcp_get_available_congestion_control(char *buf, size_t maxlen)
157{
158 struct tcp_congestion_ops *ca;
159 size_t offs = 0;
160
161 rcu_read_lock();
162 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
163 offs += snprintf(buf + offs, maxlen - offs,
164 "%s%s",
165 offs == 0 ? "" : " ", ca->name);
3ff825b2
SH
166 }
167 rcu_read_unlock();
168}
169
317a76f9
SH
170/* Get current default congestion control */
171void tcp_get_default_congestion_control(char *name)
172{
173 struct tcp_congestion_ops *ca;
174 /* We will always have reno... */
175 BUG_ON(list_empty(&tcp_cong_list));
176
177 rcu_read_lock();
178 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
179 strncpy(name, ca->name, TCP_CA_NAME_MAX);
180 rcu_read_unlock();
181}
182
ce7bc3bf
SH
183/* Built list of non-restricted congestion control values */
184void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
185{
186 struct tcp_congestion_ops *ca;
187 size_t offs = 0;
188
189 *buf = '\0';
190 rcu_read_lock();
191 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
164891aa 192 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
ce7bc3bf
SH
193 continue;
194 offs += snprintf(buf + offs, maxlen - offs,
195 "%s%s",
196 offs == 0 ? "" : " ", ca->name);
ce7bc3bf
SH
197 }
198 rcu_read_unlock();
199}
200
201/* Change list of non-restricted congestion control */
202int tcp_set_allowed_congestion_control(char *val)
203{
204 struct tcp_congestion_ops *ca;
c34186ed 205 char *saved_clone, *clone, *name;
ce7bc3bf
SH
206 int ret = 0;
207
c34186ed 208 saved_clone = clone = kstrdup(val, GFP_USER);
ce7bc3bf
SH
209 if (!clone)
210 return -ENOMEM;
211
212 spin_lock(&tcp_cong_list_lock);
213 /* pass 1 check for bad entries */
214 while ((name = strsep(&clone, " ")) && *name) {
215 ca = tcp_ca_find(name);
216 if (!ca) {
217 ret = -ENOENT;
218 goto out;
219 }
220 }
221
164891aa 222 /* pass 2 clear old values */
ce7bc3bf 223 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
164891aa 224 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
ce7bc3bf
SH
225
226 /* pass 3 mark as allowed */
227 while ((name = strsep(&val, " ")) && *name) {
228 ca = tcp_ca_find(name);
229 WARN_ON(!ca);
230 if (ca)
164891aa 231 ca->flags |= TCP_CONG_NON_RESTRICTED;
ce7bc3bf
SH
232 }
233out:
234 spin_unlock(&tcp_cong_list_lock);
c34186ed 235 kfree(saved_clone);
ce7bc3bf
SH
236
237 return ret;
238}
239
5f8ef48d 240/* Change congestion control for socket */
6687e988 241int tcp_set_congestion_control(struct sock *sk, const char *name)
5f8ef48d 242{
6687e988 243 struct inet_connection_sock *icsk = inet_csk(sk);
5f8ef48d
SH
244 struct tcp_congestion_ops *ca;
245 int err = 0;
246
247 rcu_read_lock();
248 ca = tcp_ca_find(name);
4d4d3d1e 249
35bfbc94 250 /* no change asking for existing value */
6687e988 251 if (ca == icsk->icsk_ca_ops)
5f8ef48d
SH
252 goto out;
253
95a5afca 254#ifdef CONFIG_MODULES
35bfbc94 255 /* not found attempt to autoload module */
a8f80e8f 256 if (!ca && capable(CAP_NET_ADMIN)) {
35bfbc94
SH
257 rcu_read_unlock();
258 request_module("tcp_%s", name);
259 rcu_read_lock();
260 ca = tcp_ca_find(name);
261 }
262#endif
5f8ef48d
SH
263 if (!ca)
264 err = -ENOENT;
265
52e804c6
EB
266 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
267 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
ce7bc3bf
SH
268 err = -EPERM;
269
5f8ef48d
SH
270 else if (!try_module_get(ca->owner))
271 err = -EBUSY;
272
273 else {
6687e988
ACM
274 tcp_cleanup_congestion_control(sk);
275 icsk->icsk_ca_ops = ca;
4d4d3d1e
SH
276
277 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
6687e988 278 icsk->icsk_ca_ops->init(sk);
5f8ef48d
SH
279 }
280 out:
281 rcu_read_unlock();
282 return err;
283}
284
9f9843a7
YC
285/* Slow start is used when congestion window is no greater than the slow start
286 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
287 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
288 * something better;) a packet is only considered (s)acked in its entirety to
289 * defend the ACK attacks described in the RFC. Slow start processes a stretch
290 * ACK of degree N as if N acks of degree 1 are received back to back except
291 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
292 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
40efc6fa 293 */
a12a601e 294void tcp_slow_start(struct tcp_sock *tp, u32 acked)
40efc6fa 295{
9f9843a7 296 u32 cwnd = tp->snd_cwnd + acked;
a02ba041 297
9f9843a7
YC
298 if (cwnd > tp->snd_ssthresh)
299 cwnd = tp->snd_ssthresh + 1;
9f9843a7 300 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
40efc6fa
SH
301}
302EXPORT_SYMBOL_GPL(tcp_slow_start);
303
758ce5c8
IJ
304/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
305void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
306{
307 if (tp->snd_cwnd_cnt >= w) {
308 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
309 tp->snd_cwnd++;
310 tp->snd_cwnd_cnt = 0;
311 } else {
312 tp->snd_cwnd_cnt++;
313 }
314}
315EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
316
317a76f9
SH
317/*
318 * TCP Reno congestion control
319 * This is special case used for fallback as well.
320 */
321/* This is Jacobson's slow start and congestion avoidance.
322 * SIGCOMM '88, p. 328.
323 */
24901551 324void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
317a76f9 325{
6687e988
ACM
326 struct tcp_sock *tp = tcp_sk(sk);
327
24901551 328 if (!tcp_is_cwnd_limited(sk))
317a76f9
SH
329 return;
330
7faffa1c 331 /* In "safe" area, increase. */
e905a9ed 332 if (tp->snd_cwnd <= tp->snd_ssthresh)
9f9843a7 333 tcp_slow_start(tp, acked);
e905a9ed 334 /* In dangerous area, increase slowly. */
ca2eb567 335 else
758ce5c8 336 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
317a76f9
SH
337}
338EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
339
340/* Slow start threshold is half the congestion window (min 2) */
6687e988 341u32 tcp_reno_ssthresh(struct sock *sk)
317a76f9 342{
6687e988 343 const struct tcp_sock *tp = tcp_sk(sk);
688d1945 344
317a76f9
SH
345 return max(tp->snd_cwnd >> 1U, 2U);
346}
347EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
348
317a76f9 349struct tcp_congestion_ops tcp_reno = {
164891aa 350 .flags = TCP_CONG_NON_RESTRICTED,
317a76f9
SH
351 .name = "reno",
352 .owner = THIS_MODULE,
353 .ssthresh = tcp_reno_ssthresh,
354 .cong_avoid = tcp_reno_cong_avoid,
317a76f9 355};