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1
2#define pr_fmt(fmt) "list_sort_test: " fmt
3
4#include <linux/kernel.h>
5#include <linux/bug.h>
6#include <linux/compiler.h>
7#include <linux/export.h>
8#include <linux/string.h>
9#include <linux/list_sort.h>
10#include <linux/list.h>
11
12#define MAX_LIST_LENGTH_BITS 20
13
14/*
15 * Returns a list organized in an intermediate format suited
16 * to chaining of merge() calls: null-terminated, no reserved or
17 * sentinel head node, "prev" links not maintained.
18 */
19static struct list_head *merge(void *priv,
20 int (*cmp)(void *priv, struct list_head *a,
21 struct list_head *b),
22 struct list_head *a, struct list_head *b)
23{
24 struct list_head head, *tail = &head;
25
26 while (a && b) {
27 /* if equal, take 'a' -- important for sort stability */
28 if ((*cmp)(priv, a, b) <= 0) {
29 tail->next = a;
30 a = a->next;
31 } else {
32 tail->next = b;
33 b = b->next;
34 }
35 tail = tail->next;
36 }
37 tail->next = a?:b;
38 return head.next;
39}
40
41/*
42 * Combine final list merge with restoration of standard doubly-linked
43 * list structure. This approach duplicates code from merge(), but
44 * runs faster than the tidier alternatives of either a separate final
45 * prev-link restoration pass, or maintaining the prev links
46 * throughout.
47 */
48static void merge_and_restore_back_links(void *priv,
49 int (*cmp)(void *priv, struct list_head *a,
50 struct list_head *b),
51 struct list_head *head,
52 struct list_head *a, struct list_head *b)
53{
54 struct list_head *tail = head;
55 u8 count = 0;
56
57 while (a && b) {
58 /* if equal, take 'a' -- important for sort stability */
59 if ((*cmp)(priv, a, b) <= 0) {
60 tail->next = a;
61 a->prev = tail;
62 a = a->next;
63 } else {
64 tail->next = b;
65 b->prev = tail;
66 b = b->next;
67 }
68 tail = tail->next;
69 }
70 tail->next = a ? : b;
71
72 do {
73 /*
74 * In worst cases this loop may run many iterations.
75 * Continue callbacks to the client even though no
76 * element comparison is needed, so the client's cmp()
77 * routine can invoke cond_resched() periodically.
78 */
79 if (unlikely(!(++count)))
80 (*cmp)(priv, tail->next, tail->next);
81
82 tail->next->prev = tail;
83 tail = tail->next;
84 } while (tail->next);
85
86 tail->next = head;
87 head->prev = tail;
88}
89
90/**
91 * list_sort - sort a list
92 * @priv: private data, opaque to list_sort(), passed to @cmp
93 * @head: the list to sort
94 * @cmp: the elements comparison function
95 *
96 * This function implements "merge sort", which has O(nlog(n))
97 * complexity.
98 *
99 * The comparison function @cmp must return a negative value if @a
100 * should sort before @b, and a positive value if @a should sort after
101 * @b. If @a and @b are equivalent, and their original relative
102 * ordering is to be preserved, @cmp must return 0.
103 */
104void list_sort(void *priv, struct list_head *head,
105 int (*cmp)(void *priv, struct list_head *a,
106 struct list_head *b))
107{
108 struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
109 -- last slot is a sentinel */
110 int lev; /* index into part[] */
111 int max_lev = 0;
112 struct list_head *list;
113
114 if (list_empty(head))
115 return;
116
117 memset(part, 0, sizeof(part));
118
119 head->prev->next = NULL;
120 list = head->next;
121
122 while (list) {
123 struct list_head *cur = list;
124 list = list->next;
125 cur->next = NULL;
126
127 for (lev = 0; part[lev]; lev++) {
128 cur = merge(priv, cmp, part[lev], cur);
129 part[lev] = NULL;
130 }
131 if (lev > max_lev) {
132 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
133 printk_once(KERN_DEBUG "list too long for efficiency\n");
134 lev--;
135 }
136 max_lev = lev;
137 }
138 part[lev] = cur;
139 }
140
141 for (lev = 0; lev < max_lev; lev++)
142 if (part[lev])
143 list = merge(priv, cmp, part[lev], list);
144
145 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
146}
147EXPORT_SYMBOL(list_sort);
148
149#ifdef CONFIG_TEST_LIST_SORT
150
151#include <linux/slab.h>
152#include <linux/random.h>
153
154/*
155 * The pattern of set bits in the list length determines which cases
156 * are hit in list_sort().
157 */
158#define TEST_LIST_LEN (512+128+2) /* not including head */
159
160#define TEST_POISON1 0xDEADBEEF
161#define TEST_POISON2 0xA324354C
162
163struct debug_el {
164 unsigned int poison1;
165 struct list_head list;
166 unsigned int poison2;
167 int value;
168 unsigned serial;
169};
170
171/* Array, containing pointers to all elements in the test list */
172static struct debug_el **elts __initdata;
173
174static int __init check(struct debug_el *ela, struct debug_el *elb)
175{
176 if (ela->serial >= TEST_LIST_LEN) {
177 pr_err("error: incorrect serial %d\n", ela->serial);
178 return -EINVAL;
179 }
180 if (elb->serial >= TEST_LIST_LEN) {
181 pr_err("error: incorrect serial %d\n", elb->serial);
182 return -EINVAL;
183 }
184 if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
185 pr_err("error: phantom element\n");
186 return -EINVAL;
187 }
188 if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
189 pr_err("error: bad poison: %#x/%#x\n",
190 ela->poison1, ela->poison2);
191 return -EINVAL;
192 }
193 if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
194 pr_err("error: bad poison: %#x/%#x\n",
195 elb->poison1, elb->poison2);
196 return -EINVAL;
197 }
198 return 0;
199}
200
201static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
202{
203 struct debug_el *ela, *elb;
204
205 ela = container_of(a, struct debug_el, list);
206 elb = container_of(b, struct debug_el, list);
207
208 check(ela, elb);
209 return ela->value - elb->value;
210}
211
212static int __init list_sort_test(void)
213{
214 int i, count = 1, err = -ENOMEM;
215 struct debug_el *el;
216 struct list_head *cur;
217 LIST_HEAD(head);
218
219 pr_debug("start testing list_sort()\n");
220
221 elts = kcalloc(TEST_LIST_LEN, sizeof(*elts), GFP_KERNEL);
222 if (!elts) {
223 pr_err("error: cannot allocate memory\n");
224 return err;
225 }
226
227 for (i = 0; i < TEST_LIST_LEN; i++) {
228 el = kmalloc(sizeof(*el), GFP_KERNEL);
229 if (!el) {
230 pr_err("error: cannot allocate memory\n");
231 goto exit;
232 }
233 /* force some equivalencies */
234 el->value = prandom_u32() % (TEST_LIST_LEN / 3);
235 el->serial = i;
236 el->poison1 = TEST_POISON1;
237 el->poison2 = TEST_POISON2;
238 elts[i] = el;
239 list_add_tail(&el->list, &head);
240 }
241
242 list_sort(NULL, &head, cmp);
243
244 err = -EINVAL;
245 for (cur = head.next; cur->next != &head; cur = cur->next) {
246 struct debug_el *el1;
247 int cmp_result;
248
249 if (cur->next->prev != cur) {
250 pr_err("error: list is corrupted\n");
251 goto exit;
252 }
253
254 cmp_result = cmp(NULL, cur, cur->next);
255 if (cmp_result > 0) {
256 pr_err("error: list is not sorted\n");
257 goto exit;
258 }
259
260 el = container_of(cur, struct debug_el, list);
261 el1 = container_of(cur->next, struct debug_el, list);
262 if (cmp_result == 0 && el->serial >= el1->serial) {
263 pr_err("error: order of equivalent elements not "
264 "preserved\n");
265 goto exit;
266 }
267
268 if (check(el, el1)) {
269 pr_err("error: element check failed\n");
270 goto exit;
271 }
272 count++;
273 }
274 if (head.prev != cur) {
275 pr_err("error: list is corrupted\n");
276 goto exit;
277 }
278
279
280 if (count != TEST_LIST_LEN) {
281 pr_err("error: bad list length %d", count);
282 goto exit;
283 }
284
285 err = 0;
286exit:
287 for (i = 0; i < TEST_LIST_LEN; i++)
288 kfree(elts[i]);
289 kfree(elts);
290 return err;
291}
292late_initcall(list_sort_test);
293#endif /* CONFIG_TEST_LIST_SORT */
1// SPDX-License-Identifier: GPL-2.0
2#include <linux/kernel.h>
3#include <linux/bug.h>
4#include <linux/compiler.h>
5#include <linux/export.h>
6#include <linux/string.h>
7#include <linux/list_sort.h>
8#include <linux/list.h>
9
10#define MAX_LIST_LENGTH_BITS 20
11
12/*
13 * Returns a list organized in an intermediate format suited
14 * to chaining of merge() calls: null-terminated, no reserved or
15 * sentinel head node, "prev" links not maintained.
16 */
17static struct list_head *merge(void *priv,
18 int (*cmp)(void *priv, struct list_head *a,
19 struct list_head *b),
20 struct list_head *a, struct list_head *b)
21{
22 struct list_head head, *tail = &head;
23
24 while (a && b) {
25 /* if equal, take 'a' -- important for sort stability */
26 if ((*cmp)(priv, a, b) <= 0) {
27 tail->next = a;
28 a = a->next;
29 } else {
30 tail->next = b;
31 b = b->next;
32 }
33 tail = tail->next;
34 }
35 tail->next = a?:b;
36 return head.next;
37}
38
39/*
40 * Combine final list merge with restoration of standard doubly-linked
41 * list structure. This approach duplicates code from merge(), but
42 * runs faster than the tidier alternatives of either a separate final
43 * prev-link restoration pass, or maintaining the prev links
44 * throughout.
45 */
46static void merge_and_restore_back_links(void *priv,
47 int (*cmp)(void *priv, struct list_head *a,
48 struct list_head *b),
49 struct list_head *head,
50 struct list_head *a, struct list_head *b)
51{
52 struct list_head *tail = head;
53 u8 count = 0;
54
55 while (a && b) {
56 /* if equal, take 'a' -- important for sort stability */
57 if ((*cmp)(priv, a, b) <= 0) {
58 tail->next = a;
59 a->prev = tail;
60 a = a->next;
61 } else {
62 tail->next = b;
63 b->prev = tail;
64 b = b->next;
65 }
66 tail = tail->next;
67 }
68 tail->next = a ? : b;
69
70 do {
71 /*
72 * In worst cases this loop may run many iterations.
73 * Continue callbacks to the client even though no
74 * element comparison is needed, so the client's cmp()
75 * routine can invoke cond_resched() periodically.
76 */
77 if (unlikely(!(++count)))
78 (*cmp)(priv, tail->next, tail->next);
79
80 tail->next->prev = tail;
81 tail = tail->next;
82 } while (tail->next);
83
84 tail->next = head;
85 head->prev = tail;
86}
87
88/**
89 * list_sort - sort a list
90 * @priv: private data, opaque to list_sort(), passed to @cmp
91 * @head: the list to sort
92 * @cmp: the elements comparison function
93 *
94 * This function implements "merge sort", which has O(nlog(n))
95 * complexity.
96 *
97 * The comparison function @cmp must return a negative value if @a
98 * should sort before @b, and a positive value if @a should sort after
99 * @b. If @a and @b are equivalent, and their original relative
100 * ordering is to be preserved, @cmp must return 0.
101 */
102void list_sort(void *priv, struct list_head *head,
103 int (*cmp)(void *priv, struct list_head *a,
104 struct list_head *b))
105{
106 struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
107 -- last slot is a sentinel */
108 int lev; /* index into part[] */
109 int max_lev = 0;
110 struct list_head *list;
111
112 if (list_empty(head))
113 return;
114
115 memset(part, 0, sizeof(part));
116
117 head->prev->next = NULL;
118 list = head->next;
119
120 while (list) {
121 struct list_head *cur = list;
122 list = list->next;
123 cur->next = NULL;
124
125 for (lev = 0; part[lev]; lev++) {
126 cur = merge(priv, cmp, part[lev], cur);
127 part[lev] = NULL;
128 }
129 if (lev > max_lev) {
130 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
131 printk_once(KERN_DEBUG "list too long for efficiency\n");
132 lev--;
133 }
134 max_lev = lev;
135 }
136 part[lev] = cur;
137 }
138
139 for (lev = 0; lev < max_lev; lev++)
140 if (part[lev])
141 list = merge(priv, cmp, part[lev], list);
142
143 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
144}
145EXPORT_SYMBOL(list_sort);