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
30 static struct plist_head test_head;
31
plist_check_prev_next(struct list_head * t,struct list_head * p,struct list_head * n)32 static 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
plist_check_list(struct list_head * top)44 static 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
plist_check_head(struct plist_head * head)56 static 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 */
plist_add(struct plist_node * node,struct plist_head * head)73 void 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(&node->prio_list, &iter->prio_list);
110 ins_node:
111 list_add_tail(&node->node_list, 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 */
plist_del(struct plist_node * node,struct plist_head * head)122 void plist_del(struct plist_node *node, struct plist_head *head)
123 {
124 plist_check_head(head);
125
126 if (!list_empty(&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(&next->prio_list))
135 list_add(&next->prio_list, &node->prio_list);
136 }
137 list_del_init(&node->prio_list);
138 }
139
140 list_del_init(&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 */
plist_requeue(struct plist_node * node,struct plist_head * head)155 void 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 plist_for_each_continue(iter, head) {
175 if (node->prio != iter->prio) {
176 node_next = &iter->node_list;
177 break;
178 }
179 }
180 list_add_tail(&node->node_list, node_next);
181
182 plist_check_head(head);
183 }
184
185 #ifdef CONFIG_DEBUG_PLIST
186 #include <linux/sched.h>
187 #include <linux/sched/clock.h>
188 #include <linux/module.h>
189 #include <linux/init.h>
190
191 static struct plist_node __initdata test_node[241];
192
plist_test_check(int nr_expect)193 static void __init plist_test_check(int nr_expect)
194 {
195 struct plist_node *first, *prio_pos, *node_pos;
196
197 if (plist_head_empty(&test_head)) {
198 BUG_ON(nr_expect != 0);
199 return;
200 }
201
202 prio_pos = first = plist_first(&test_head);
203 plist_for_each(node_pos, &test_head) {
204 if (nr_expect-- < 0)
205 break;
206 if (node_pos == first)
207 continue;
208 if (node_pos->prio == prio_pos->prio) {
209 BUG_ON(!list_empty(&node_pos->prio_list));
210 continue;
211 }
212
213 BUG_ON(prio_pos->prio > node_pos->prio);
214 BUG_ON(prio_pos->prio_list.next != &node_pos->prio_list);
215 prio_pos = node_pos;
216 }
217
218 BUG_ON(nr_expect != 0);
219 BUG_ON(prio_pos->prio_list.next != &first->prio_list);
220 }
221
plist_test_requeue(struct plist_node * node)222 static void __init plist_test_requeue(struct plist_node *node)
223 {
224 plist_requeue(node, &test_head);
225
226 if (node != plist_last(&test_head))
227 BUG_ON(node->prio == plist_next(node)->prio);
228 }
229
plist_test(void)230 static int __init plist_test(void)
231 {
232 int nr_expect = 0, i, loop;
233 unsigned int r = local_clock();
234
235 printk(KERN_DEBUG "start plist test\n");
236 plist_head_init(&test_head);
237 for (i = 0; i < ARRAY_SIZE(test_node); i++)
238 plist_node_init(test_node + i, 0);
239
240 for (loop = 0; loop < 1000; loop++) {
241 r = r * 193939 % 47629;
242 i = r % ARRAY_SIZE(test_node);
243 if (plist_node_empty(test_node + i)) {
244 r = r * 193939 % 47629;
245 test_node[i].prio = r % 99;
246 plist_add(test_node + i, &test_head);
247 nr_expect++;
248 } else {
249 plist_del(test_node + i, &test_head);
250 nr_expect--;
251 }
252 plist_test_check(nr_expect);
253 if (!plist_node_empty(test_node + i)) {
254 plist_test_requeue(test_node + i);
255 plist_test_check(nr_expect);
256 }
257 }
258
259 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
260 if (plist_node_empty(test_node + i))
261 continue;
262 plist_del(test_node + i, &test_head);
263 nr_expect--;
264 plist_test_check(nr_expect);
265 }
266
267 printk(KERN_DEBUG "end plist test\n");
268
269 /* Worst case test for plist_add() */
270 unsigned int test_data[241];
271
272 for (i = 0; i < ARRAY_SIZE(test_data); i++)
273 test_data[i] = i;
274
275 ktime_t start, end, time_elapsed = 0;
276
277 plist_head_init(&test_head);
278
279 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
280 plist_node_init(test_node + i, 0);
281 test_node[i].prio = test_data[i];
282 }
283
284 for (i = 0; i < ARRAY_SIZE(test_node); i++) {
285 if (plist_node_empty(test_node + i)) {
286 start = ktime_get();
287 plist_add(test_node + i, &test_head);
288 end = ktime_get();
289 time_elapsed += (end - start);
290 }
291 }
292
293 pr_debug("plist_add worst case test time elapsed %lld\n", time_elapsed);
294 return 0;
295 }
296
297 module_init(plist_test);
298
299 #endif
300