1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * IPVS:        Round-Robin Scheduling module
4 *
5 * Authors:     Wensong Zhang <wensong@linuxvirtualserver.org>
6 *              Peter Kese <peter.kese@ijs.si>
7 *
8 * Fixes/Changes:
9 *     Wensong Zhang            :     changed the ip_vs_rr_schedule to return dest
10 *     Julian Anastasov         :     fixed the NULL pointer access bug in debugging
11 *     Wensong Zhang            :     changed some comestics things for debugging
12 *     Wensong Zhang            :     changed for the d-linked destination list
13 *     Wensong Zhang            :     added the ip_vs_rr_update_svc
14 *     Wensong Zhang            :     added any dest with weight=0 is quiesced
15 */
16
17#define KMSG_COMPONENT "IPVS"
18#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
19
20#include <linux/module.h>
21#include <linux/kernel.h>
22
23#include <net/ip_vs.h>
24
25
26static int ip_vs_rr_init_svc(struct ip_vs_service *svc)
27{
28	svc->sched_data = &svc->destinations;
29	return 0;
30}
31
32
33static int ip_vs_rr_del_dest(struct ip_vs_service *svc, struct ip_vs_dest *dest)
34{
35	struct list_head *p;
36
37	spin_lock_bh(&svc->sched_lock);
38	p = (struct list_head *) svc->sched_data;
39	/* dest is already unlinked, so p->prev is not valid but
40	 * p->next is valid, use it to reach previous entry.
41	 */
42	if (p == &dest->n_list)
43		svc->sched_data = p->next->prev;
44	spin_unlock_bh(&svc->sched_lock);
45	return 0;
46}
47
48
49/*
50 * Round-Robin Scheduling
51 */
52static struct ip_vs_dest *
53ip_vs_rr_schedule(struct ip_vs_service *svc, const struct sk_buff *skb,
54		  struct ip_vs_iphdr *iph)
55{
56	struct list_head *p;
57	struct ip_vs_dest *dest, *last;
58	int pass = 0;
59
60	IP_VS_DBG(6, "%s(): Scheduling...\n", __func__);
61
62	spin_lock_bh(&svc->sched_lock);
63	p = (struct list_head *) svc->sched_data;
64	last = dest = list_entry(p, struct ip_vs_dest, n_list);
65
66	do {
67		list_for_each_entry_continue_rcu(dest,
68						 &svc->destinations,
69						 n_list) {
70			if (!(dest->flags & IP_VS_DEST_F_OVERLOAD) &&
71			    atomic_read(&dest->weight) > 0)
72				/* HIT */
73				goto out;
74			if (dest == last)
75				goto stop;
76		}
77		pass++;
78		/* Previous dest could be unlinked, do not loop forever.
79		 * If we stay at head there is no need for 2nd pass.
80		 */
81	} while (pass < 2 && p != &svc->destinations);
82
83stop:
84	spin_unlock_bh(&svc->sched_lock);
85	ip_vs_scheduler_err(svc, "no destination available");
86	return NULL;
87
88  out:
89	svc->sched_data = &dest->n_list;
90	spin_unlock_bh(&svc->sched_lock);
91	IP_VS_DBG_BUF(6, "RR: server %s:%u "
92		      "activeconns %d refcnt %d weight %d\n",
93		      IP_VS_DBG_ADDR(dest->af, &dest->addr), ntohs(dest->port),
94		      atomic_read(&dest->activeconns),
95		      refcount_read(&dest->refcnt), atomic_read(&dest->weight));
96
97	return dest;
98}
99
100
101static struct ip_vs_scheduler ip_vs_rr_scheduler = {
102	.name =			"rr",			/* name */
103	.refcnt =		ATOMIC_INIT(0),
104	.module =		THIS_MODULE,
105	.n_list =		LIST_HEAD_INIT(ip_vs_rr_scheduler.n_list),
106	.init_service =		ip_vs_rr_init_svc,
107	.add_dest =		NULL,
108	.del_dest =		ip_vs_rr_del_dest,
109	.schedule =		ip_vs_rr_schedule,
110};
111
112static int __init ip_vs_rr_init(void)
113{
114	return register_ip_vs_scheduler(&ip_vs_rr_scheduler);
115}
116
117static void __exit ip_vs_rr_cleanup(void)
118{
119	unregister_ip_vs_scheduler(&ip_vs_rr_scheduler);
120	synchronize_rcu();
121}
122
123module_init(ip_vs_rr_init);
124module_exit(ip_vs_rr_cleanup);
125MODULE_DESCRIPTION("ipvs round-robin scheduler");
126MODULE_LICENSE("GPL");
127