1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * lib/plist.c
4 *
5 * Descending-priority-sorted double-linked list
6 *
7 * (C) 2002-2003 Intel Corp
8 * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>.
9 *
10 * 2001-2005 (c) MontaVista Software, Inc.
11 * Daniel Walker <dwalker@mvista.com>
12 *
13 * (C) 2005 Thomas Gleixner <tglx@linutronix.de>
14 *
15 * Simplifications of the original code by
16 * Oleg Nesterov <oleg@tv-sign.ru>
17 *
18 * Based on simple lists (include/linux/list.h).
19 *
20 * This file contains the add / del functions which are considered to
21 * be too large to inline. See include/linux/plist.h for further
22 * information.
23 */
24
25#include <linux/bug.h>
26#include <linux/plist.h>
27
28#ifdef CONFIG_DEBUG_PLIST
29
30static struct plist_head test_head;
31
32static void plist_check_prev_next(struct list_head *t, struct list_head *p,
33 struct list_head *n)
34{
35 WARN(n->prev != p || p->next != n,
36 "top: %p, n: %p, p: %p\n"
37 "prev: %p, n: %p, p: %p\n"
38 "next: %p, n: %p, p: %p\n",
39 t, t->next, t->prev,
40 p, p->next, p->prev,
41 n, n->next, n->prev);
42}
43
44static void plist_check_list(struct list_head *top)
45{
46 struct list_head *prev = top, *next = top->next;
47
48 plist_check_prev_next(top, prev, next);
49 while (next != top) {
50 WRITE_ONCE(prev, next);
51 WRITE_ONCE(next, prev->next);
52 plist_check_prev_next(top, prev, next);
53 }
54}
55
56static void plist_check_head(struct plist_head *head)
57{
58 if (!plist_head_empty(head))
59 plist_check_list(&plist_first(head)->prio_list);
60 plist_check_list(&head->node_list);
61}
62
63#else
64# define plist_check_head(h) do { } while (0)
65#endif
66
67/**
68 * plist_add - add @node to @head
69 *
70 * @node: &struct plist_node pointer
71 * @head: &struct plist_head pointer
72 */
73void plist_add(struct plist_node *node, struct plist_head *head)
74{
75 struct plist_node *first, *iter, *prev = NULL, *last, *reverse_iter;
76 struct list_head *node_next = &head->node_list;
77
78 plist_check_head(head);
79 WARN_ON(!plist_node_empty(node));
80 WARN_ON(!list_empty(&node->prio_list));
81
82 if (plist_head_empty(head))
83 goto ins_node;
84
85 first = iter = plist_first(head);
86 last = reverse_iter = list_entry(first->prio_list.prev, struct plist_node, prio_list);
87
88 do {
89 if (node->prio < iter->prio) {
90 node_next = &iter->node_list;
91 break;
92 } else if (node->prio >= reverse_iter->prio) {
93 prev = reverse_iter;
94 iter = list_entry(reverse_iter->prio_list.next,
95 struct plist_node, prio_list);
96 if (likely(reverse_iter != last))
97 node_next = &iter->node_list;
98 break;
99 }
100
101 prev = iter;
102 iter = list_entry(iter->prio_list.next,
103 struct plist_node, prio_list);
104 reverse_iter = list_entry(reverse_iter->prio_list.prev,
105 struct plist_node, prio_list);
106 } while (iter != first);
107
108 if (!prev || prev->prio != node->prio)
109 list_add_tail(new: &node->prio_list, head: &iter->prio_list);
110ins_node:
111 list_add_tail(new: &node->node_list, head: node_next);
112
113 plist_check_head(head);
114}
115
116/**
117 * plist_del - Remove a @node from plist.
118 *
119 * @node: &struct plist_node pointer - entry to be removed
120 * @head: &struct plist_head pointer - list head
121 */
122void plist_del(struct plist_node *node, struct plist_head *head)
123{
124 plist_check_head(head);
125
126 if (!list_empty(head: &node->prio_list)) {
127 if (node->node_list.next != &head->node_list) {
128 struct plist_node *next;
129
130 next = list_entry(node->node_list.next,
131 struct plist_node, node_list);
132
133 /* add the next plist_node into prio_list */
134 if (list_empty(head: &next->prio_list))
135 list_add(new: &next->prio_list, head: &node->prio_list);
136 }
137 list_del_init(entry: &node->prio_list);
138 }
139
140 list_del_init(entry: &node->node_list);
141
142 plist_check_head(head);
143}
144
145/**
146 * plist_requeue - Requeue @node at end of same-prio entries.
147 *
148 * This is essentially an optimized plist_del() followed by
149 * plist_add(). It moves an entry already in the plist to
150 * after any other same-priority entries.
151 *
152 * @node: &struct plist_node pointer - entry to be moved
153 * @head: &struct plist_head pointer - list head
154 */
155void plist_requeue(struct plist_node *node, struct plist_head *head)
156{
157 struct plist_node *iter;
158 struct list_head *node_next = &head->node_list;
159
160 plist_check_head(head);
161 BUG_ON(plist_head_empty(head));
162 BUG_ON(plist_node_empty(node));
163
164 if (node == plist_last(head))
165 return;
166
167 iter = plist_next(node);
168
169 if (node->prio != iter->prio)
170 return;
171
172 plist_del(node, head);
173
174 /*
175 * After plist_del(), iter is the replacement of the node. If the node
176 * was on prio_list, take shortcut to find node_next instead of looping.
177 */
178 if (!list_empty(head: &iter->prio_list)) {
179 iter = list_entry(iter->prio_list.next, struct plist_node,
180 prio_list);
181 node_next = &iter->node_list;
182 goto queue;
183 }
184
185 plist_for_each_continue(iter, head) {
186 if (node->prio != iter->prio) {
187 node_next = &iter->node_list;
188 break;
189 }
190 }
191queue:
192 list_add_tail(new: &node->node_list, head: node_next);
193
194 plist_check_head(head);
195}
196
197#ifdef CONFIG_DEBUG_PLIST
198#include <linux/sched.h>
199#include <linux/sched/clock.h>
200#include <linux/module.h>
201#include <linux/init.h>
202
203static struct plist_node __initdata test_node[241];
204
205static void __init plist_test_check(int nr_expect)
206{
207 struct plist_node *first, *prio_pos, *node_pos;
208
209 if (plist_head_empty(&test_head)) {
210 BUG_ON(nr_expect != 0);
211 return;
212 }
213
214 prio_pos = first = plist_first(&test_head);
215 plist_for_each(node_pos, &test_head) {
216 if (nr_expect-- < 0)
217 break;
218 if (node_pos == first)
219 continue;
220 if (node_pos->prio == prio_pos->prio) {
221 BUG_ON(!list_empty(&node_pos->prio_list));
222 continue;
223 }
224
225 BUG_ON(prio_pos->prio > node_pos->prio);
226 BUG_ON(prio_pos->prio_list.next != &node_pos->prio_list);
227 prio_pos = node_pos;
228 }
229
230 BUG_ON(nr_expect != 0);
231 BUG_ON(prio_pos->prio_list.next != &first->prio_list);
232}
233
234static void __init plist_test_requeue(struct plist_node *node)
235{
236 plist_requeue(node, &test_head);
237
238 if (node != plist_last(&test_head))
239 BUG_ON(node->prio == plist_next(node)->prio);
240}
241
242static int __init plist_test(void)
243{
244 int nr_expect = 0, i, loop;
245 unsigned int r = local_clock();
246
247 printk(KERN_DEBUG "start plist test\n");
248 plist_head_init(&test_head);
249 for (i = 0; i < ARRAY_SIZE(test_node); i++)
250 plist_node_init(test_node + i, 0);
251
252 for (loop = 0; loop < 1000; loop++) {
253 r = r * 193939 % 47629;
254 i = r % ARRAY_SIZE(test_node);
255 if (plist_node_empty(test_node + i)) {
256 r = r * 193939 % 47629;
257 test_node[i].prio = r % 99;
258 plist_add(test_node + i, &test_head);
259 nr_expect++;
260 } else {
261 plist_del(test_node + i, &test_head);
262 nr_expect--;
263 }
264 plist_test_check(nr_expect);
265 if (!plist_node_empty(test_node + i)) {
266 plist_test_requeue(test_node + i);
267 plist_test_check(nr_expect);
268 }
269 }
270
271 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
272 if (plist_node_empty(test_node + i))
273 continue;
274 plist_del(test_node + i, &test_head);
275 nr_expect--;
276 plist_test_check(nr_expect);
277 }
278
279 printk(KERN_DEBUG "end plist test\n");
280
281 /* Worst case test for plist_add() */
282 unsigned int test_data[241];
283
284 for (i = 0; i < ARRAY_SIZE(test_data); i++)
285 test_data[i] = i;
286
287 ktime_t start, end, time_elapsed = 0;
288
289 plist_head_init(&test_head);
290
291 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
292 plist_node_init(test_node + i, 0);
293 test_node[i].prio = test_data[i];
294 }
295
296 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
297 if (plist_node_empty(test_node + i)) {
298 start = ktime_get();
299 plist_add(test_node + i, &test_head);
300 end = ktime_get();
301 time_elapsed += (end - start);
302 }
303 }
304
305 pr_debug("plist_add worst case test time elapsed %lld\n", time_elapsed);
306 return 0;
307}
308
309module_init(plist_test);
310
311#endif
312