1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * net/sched/sch_choke.c	CHOKE scheduler
4 *
5 * Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
6 * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
7 */
8
9#include <linux/module.h>
10#include <linux/types.h>
11#include <linux/kernel.h>
12#include <linux/skbuff.h>
13#include <linux/vmalloc.h>
14#include <net/pkt_sched.h>
15#include <net/pkt_cls.h>
16#include <net/inet_ecn.h>
17#include <net/red.h>
18#include <net/flow_dissector.h>
19
20/*
21   CHOKe stateless AQM for fair bandwidth allocation
22   =================================================
23
24   CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
25   unresponsive flows) is a variant of RED that penalizes misbehaving flows but
26   maintains no flow state. The difference from RED is an additional step
27   during the enqueuing process. If average queue size is over the
28   low threshold (qmin), a packet is chosen at random from the queue.
29   If both the new and chosen packet are from the same flow, both
30   are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
31   needs to access packets in queue randomly. It has a minimal class
32   interface to allow overriding the builtin flow classifier with
33   filters.
34
35   Source:
36   R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
37   Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
38   IEEE INFOCOM, 2000.
39
40   A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
41   Characteristics", IEEE/ACM Transactions on Networking, 2004
42
43 */
44
45/* Upper bound on size of sk_buff table (packets) */
46#define CHOKE_MAX_QUEUE	(128*1024 - 1)
47
48struct choke_sched_data {
49/* Parameters */
50	u32		 limit;
51	unsigned char	 flags;
52
53	struct red_parms parms;
54
55/* Variables */
56	struct red_vars  vars;
57	struct {
58		u32	prob_drop;	/* Early probability drops */
59		u32	prob_mark;	/* Early probability marks */
60		u32	forced_drop;	/* Forced drops, qavg > max_thresh */
61		u32	forced_mark;	/* Forced marks, qavg > max_thresh */
62		u32	pdrop;          /* Drops due to queue limits */
63		u32	matched;	/* Drops to flow match */
64	} stats;
65
66	unsigned int	 head;
67	unsigned int	 tail;
68
69	unsigned int	 tab_mask; /* size - 1 */
70
71	struct sk_buff **tab;
72};
73
74/* number of elements in queue including holes */
75static unsigned int choke_len(const struct choke_sched_data *q)
76{
77	return (q->tail - q->head) & q->tab_mask;
78}
79
80/* Is ECN parameter configured */
81static int use_ecn(const struct choke_sched_data *q)
82{
83	return q->flags & TC_RED_ECN;
84}
85
86/* Should packets over max just be dropped (versus marked) */
87static int use_harddrop(const struct choke_sched_data *q)
88{
89	return q->flags & TC_RED_HARDDROP;
90}
91
92/* Move head pointer forward to skip over holes */
93static void choke_zap_head_holes(struct choke_sched_data *q)
94{
95	do {
96		q->head = (q->head + 1) & q->tab_mask;
97		if (q->head == q->tail)
98			break;
99	} while (q->tab[q->head] == NULL);
100}
101
102/* Move tail pointer backwards to reuse holes */
103static void choke_zap_tail_holes(struct choke_sched_data *q)
104{
105	do {
106		q->tail = (q->tail - 1) & q->tab_mask;
107		if (q->head == q->tail)
108			break;
109	} while (q->tab[q->tail] == NULL);
110}
111
112/* Drop packet from queue array by creating a "hole" */
113static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
114			      struct sk_buff **to_free)
115{
116	struct choke_sched_data *q = qdisc_priv(sch);
117	struct sk_buff *skb = q->tab[idx];
118
119	q->tab[idx] = NULL;
120
121	if (idx == q->head)
122		choke_zap_head_holes(q);
123	if (idx == q->tail)
124		choke_zap_tail_holes(q);
125
126	qdisc_qstats_backlog_dec(sch, skb);
127	qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
128	qdisc_drop(skb, sch, to_free);
129	--sch->q.qlen;
130}
131
132struct choke_skb_cb {
133	u8			keys_valid;
134	struct			flow_keys_digest keys;
135};
136
137static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
138{
139	qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
140	return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
141}
142
143/*
144 * Compare flow of two packets
145 *  Returns true only if source and destination address and port match.
146 *          false for special cases
147 */
148static bool choke_match_flow(struct sk_buff *skb1,
149			     struct sk_buff *skb2)
150{
151	struct flow_keys temp;
152
153	if (skb1->protocol != skb2->protocol)
154		return false;
155
156	if (!choke_skb_cb(skb1)->keys_valid) {
157		choke_skb_cb(skb1)->keys_valid = 1;
158		skb_flow_dissect_flow_keys(skb1, &temp, 0);
159		make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
160	}
161
162	if (!choke_skb_cb(skb2)->keys_valid) {
163		choke_skb_cb(skb2)->keys_valid = 1;
164		skb_flow_dissect_flow_keys(skb2, &temp, 0);
165		make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
166	}
167
168	return !memcmp(&choke_skb_cb(skb1)->keys,
169		       &choke_skb_cb(skb2)->keys,
170		       sizeof(choke_skb_cb(skb1)->keys));
171}
172
173/*
174 * Select a packet at random from queue
175 * HACK: since queue can have holes from previous deletion; retry several
176 *   times to find a random skb but then just give up and return the head
177 * Will return NULL if queue is empty (q->head == q->tail)
178 */
179static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
180					 unsigned int *pidx)
181{
182	struct sk_buff *skb;
183	int retrys = 3;
184
185	do {
186		*pidx = (q->head + get_random_u32_below(choke_len(q))) & q->tab_mask;
187		skb = q->tab[*pidx];
188		if (skb)
189			return skb;
190	} while (--retrys > 0);
191
192	return q->tab[*pidx = q->head];
193}
194
195/*
196 * Compare new packet with random packet in queue
197 * returns true if matched and sets *pidx
198 */
199static bool choke_match_random(const struct choke_sched_data *q,
200			       struct sk_buff *nskb,
201			       unsigned int *pidx)
202{
203	struct sk_buff *oskb;
204
205	if (q->head == q->tail)
206		return false;
207
208	oskb = choke_peek_random(q, pidx);
209	return choke_match_flow(oskb, nskb);
210}
211
212static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
213			 struct sk_buff **to_free)
214{
215	struct choke_sched_data *q = qdisc_priv(sch);
216	const struct red_parms *p = &q->parms;
217
218	choke_skb_cb(skb)->keys_valid = 0;
219	/* Compute average queue usage (see RED) */
220	q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
221	if (red_is_idling(&q->vars))
222		red_end_of_idle_period(&q->vars);
223
224	/* Is queue small? */
225	if (q->vars.qavg <= p->qth_min)
226		q->vars.qcount = -1;
227	else {
228		unsigned int idx;
229
230		/* Draw a packet at random from queue and compare flow */
231		if (choke_match_random(q, skb, &idx)) {
232			q->stats.matched++;
233			choke_drop_by_idx(sch, idx, to_free);
234			goto congestion_drop;
235		}
236
237		/* Queue is large, always mark/drop */
238		if (q->vars.qavg > p->qth_max) {
239			q->vars.qcount = -1;
240
241			qdisc_qstats_overlimit(sch);
242			if (use_harddrop(q) || !use_ecn(q) ||
243			    !INET_ECN_set_ce(skb)) {
244				q->stats.forced_drop++;
245				goto congestion_drop;
246			}
247
248			q->stats.forced_mark++;
249		} else if (++q->vars.qcount) {
250			if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
251				q->vars.qcount = 0;
252				q->vars.qR = red_random(p);
253
254				qdisc_qstats_overlimit(sch);
255				if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
256					q->stats.prob_drop++;
257					goto congestion_drop;
258				}
259
260				q->stats.prob_mark++;
261			}
262		} else
263			q->vars.qR = red_random(p);
264	}
265
266	/* Admit new packet */
267	if (sch->q.qlen < q->limit) {
268		q->tab[q->tail] = skb;
269		q->tail = (q->tail + 1) & q->tab_mask;
270		++sch->q.qlen;
271		qdisc_qstats_backlog_inc(sch, skb);
272		return NET_XMIT_SUCCESS;
273	}
274
275	q->stats.pdrop++;
276	return qdisc_drop(skb, sch, to_free);
277
278congestion_drop:
279	qdisc_drop(skb, sch, to_free);
280	return NET_XMIT_CN;
281}
282
283static struct sk_buff *choke_dequeue(struct Qdisc *sch)
284{
285	struct choke_sched_data *q = qdisc_priv(sch);
286	struct sk_buff *skb;
287
288	if (q->head == q->tail) {
289		if (!red_is_idling(&q->vars))
290			red_start_of_idle_period(&q->vars);
291		return NULL;
292	}
293
294	skb = q->tab[q->head];
295	q->tab[q->head] = NULL;
296	choke_zap_head_holes(q);
297	--sch->q.qlen;
298	qdisc_qstats_backlog_dec(sch, skb);
299	qdisc_bstats_update(sch, skb);
300
301	return skb;
302}
303
304static void choke_reset(struct Qdisc *sch)
305{
306	struct choke_sched_data *q = qdisc_priv(sch);
307
308	while (q->head != q->tail) {
309		struct sk_buff *skb = q->tab[q->head];
310
311		q->head = (q->head + 1) & q->tab_mask;
312		if (!skb)
313			continue;
314		rtnl_qdisc_drop(skb, sch);
315	}
316
317	if (q->tab)
318		memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
319	q->head = q->tail = 0;
320	red_restart(&q->vars);
321}
322
323static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
324	[TCA_CHOKE_PARMS]	= { .len = sizeof(struct tc_red_qopt) },
325	[TCA_CHOKE_STAB]	= { .len = RED_STAB_SIZE },
326	[TCA_CHOKE_MAX_P]	= { .type = NLA_U32 },
327};
328
329
330static void choke_free(void *addr)
331{
332	kvfree(addr);
333}
334
335static int choke_change(struct Qdisc *sch, struct nlattr *opt,
336			struct netlink_ext_ack *extack)
337{
338	struct choke_sched_data *q = qdisc_priv(sch);
339	struct nlattr *tb[TCA_CHOKE_MAX + 1];
340	const struct tc_red_qopt *ctl;
341	int err;
342	struct sk_buff **old = NULL;
343	unsigned int mask;
344	u32 max_P;
345	u8 *stab;
346
347	if (opt == NULL)
348		return -EINVAL;
349
350	err = nla_parse_nested_deprecated(tb, TCA_CHOKE_MAX, opt,
351					  choke_policy, NULL);
352	if (err < 0)
353		return err;
354
355	if (tb[TCA_CHOKE_PARMS] == NULL ||
356	    tb[TCA_CHOKE_STAB] == NULL)
357		return -EINVAL;
358
359	max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
360
361	ctl = nla_data(tb[TCA_CHOKE_PARMS]);
362	stab = nla_data(tb[TCA_CHOKE_STAB]);
363	if (!red_check_params(ctl->qth_min, ctl->qth_max, ctl->Wlog, ctl->Scell_log, stab))
364		return -EINVAL;
365
366	if (ctl->limit > CHOKE_MAX_QUEUE)
367		return -EINVAL;
368
369	mask = roundup_pow_of_two(ctl->limit + 1) - 1;
370	if (mask != q->tab_mask) {
371		struct sk_buff **ntab;
372
373		ntab = kvcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
374		if (!ntab)
375			return -ENOMEM;
376
377		sch_tree_lock(sch);
378		old = q->tab;
379		if (old) {
380			unsigned int oqlen = sch->q.qlen, tail = 0;
381			unsigned dropped = 0;
382
383			while (q->head != q->tail) {
384				struct sk_buff *skb = q->tab[q->head];
385
386				q->head = (q->head + 1) & q->tab_mask;
387				if (!skb)
388					continue;
389				if (tail < mask) {
390					ntab[tail++] = skb;
391					continue;
392				}
393				dropped += qdisc_pkt_len(skb);
394				qdisc_qstats_backlog_dec(sch, skb);
395				--sch->q.qlen;
396				rtnl_qdisc_drop(skb, sch);
397			}
398			qdisc_tree_reduce_backlog(sch, oqlen - sch->q.qlen, dropped);
399			q->head = 0;
400			q->tail = tail;
401		}
402
403		q->tab_mask = mask;
404		q->tab = ntab;
405	} else
406		sch_tree_lock(sch);
407
408	q->flags = ctl->flags;
409	q->limit = ctl->limit;
410
411	red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
412		      ctl->Plog, ctl->Scell_log,
413		      stab,
414		      max_P);
415	red_set_vars(&q->vars);
416
417	if (q->head == q->tail)
418		red_end_of_idle_period(&q->vars);
419
420	sch_tree_unlock(sch);
421	choke_free(old);
422	return 0;
423}
424
425static int choke_init(struct Qdisc *sch, struct nlattr *opt,
426		      struct netlink_ext_ack *extack)
427{
428	return choke_change(sch, opt, extack);
429}
430
431static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
432{
433	struct choke_sched_data *q = qdisc_priv(sch);
434	struct nlattr *opts = NULL;
435	struct tc_red_qopt opt = {
436		.limit		= q->limit,
437		.flags		= q->flags,
438		.qth_min	= q->parms.qth_min >> q->parms.Wlog,
439		.qth_max	= q->parms.qth_max >> q->parms.Wlog,
440		.Wlog		= q->parms.Wlog,
441		.Plog		= q->parms.Plog,
442		.Scell_log	= q->parms.Scell_log,
443	};
444
445	opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
446	if (opts == NULL)
447		goto nla_put_failure;
448
449	if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
450	    nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
451		goto nla_put_failure;
452	return nla_nest_end(skb, opts);
453
454nla_put_failure:
455	nla_nest_cancel(skb, opts);
456	return -EMSGSIZE;
457}
458
459static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
460{
461	struct choke_sched_data *q = qdisc_priv(sch);
462	struct tc_choke_xstats st = {
463		.early	= q->stats.prob_drop + q->stats.forced_drop,
464		.marked	= q->stats.prob_mark + q->stats.forced_mark,
465		.pdrop	= q->stats.pdrop,
466		.matched = q->stats.matched,
467	};
468
469	return gnet_stats_copy_app(d, &st, sizeof(st));
470}
471
472static void choke_destroy(struct Qdisc *sch)
473{
474	struct choke_sched_data *q = qdisc_priv(sch);
475
476	choke_free(q->tab);
477}
478
479static struct sk_buff *choke_peek_head(struct Qdisc *sch)
480{
481	struct choke_sched_data *q = qdisc_priv(sch);
482
483	return (q->head != q->tail) ? q->tab[q->head] : NULL;
484}
485
486static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
487	.id		=	"choke",
488	.priv_size	=	sizeof(struct choke_sched_data),
489
490	.enqueue	=	choke_enqueue,
491	.dequeue	=	choke_dequeue,
492	.peek		=	choke_peek_head,
493	.init		=	choke_init,
494	.destroy	=	choke_destroy,
495	.reset		=	choke_reset,
496	.change		=	choke_change,
497	.dump		=	choke_dump,
498	.dump_stats	=	choke_dump_stats,
499	.owner		=	THIS_MODULE,
500};
501MODULE_ALIAS_NET_SCH("choke");
502
503static int __init choke_module_init(void)
504{
505	return register_qdisc(&choke_qdisc_ops);
506}
507
508static void __exit choke_module_exit(void)
509{
510	unregister_qdisc(&choke_qdisc_ops);
511}
512
513module_init(choke_module_init)
514module_exit(choke_module_exit)
515
516MODULE_LICENSE("GPL");
517MODULE_DESCRIPTION("Choose and keep responsive flows scheduler");
518