1
2 #define pr_fmt(fmt) "list_sort_test: " fmt
3
4 #include <linux/kernel.h>
5 #include <linux/module.h>
6 #include <linux/list_sort.h>
7 #include <linux/slab.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 */
merge(void * priv,int (* cmp)(void * priv,struct list_head * a,struct list_head * b),struct list_head * a,struct list_head * b)17 static 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 */
merge_and_restore_back_links(void * priv,int (* cmp)(void * priv,struct list_head * a,struct list_head * b),struct list_head * head,struct list_head * a,struct list_head * b)46 static 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 */
list_sort(void * priv,struct list_head * head,int (* cmp)(void * priv,struct list_head * a,struct list_head * b))102 void 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 }
145 EXPORT_SYMBOL(list_sort);
146
147 #ifdef CONFIG_TEST_LIST_SORT
148
149 #include <linux/random.h>
150
151 /*
152 * The pattern of set bits in the list length determines which cases
153 * are hit in list_sort().
154 */
155 #define TEST_LIST_LEN (512+128+2) /* not including head */
156
157 #define TEST_POISON1 0xDEADBEEF
158 #define TEST_POISON2 0xA324354C
159
160 struct debug_el {
161 unsigned int poison1;
162 struct list_head list;
163 unsigned int poison2;
164 int value;
165 unsigned serial;
166 };
167
168 /* Array, containing pointers to all elements in the test list */
169 static struct debug_el **elts __initdata;
170
check(struct debug_el * ela,struct debug_el * elb)171 static int __init check(struct debug_el *ela, struct debug_el *elb)
172 {
173 if (ela->serial >= TEST_LIST_LEN) {
174 pr_err("error: incorrect serial %d\n", ela->serial);
175 return -EINVAL;
176 }
177 if (elb->serial >= TEST_LIST_LEN) {
178 pr_err("error: incorrect serial %d\n", elb->serial);
179 return -EINVAL;
180 }
181 if (elts[ela->serial] != ela || elts[elb->serial] != elb) {
182 pr_err("error: phantom element\n");
183 return -EINVAL;
184 }
185 if (ela->poison1 != TEST_POISON1 || ela->poison2 != TEST_POISON2) {
186 pr_err("error: bad poison: %#x/%#x\n",
187 ela->poison1, ela->poison2);
188 return -EINVAL;
189 }
190 if (elb->poison1 != TEST_POISON1 || elb->poison2 != TEST_POISON2) {
191 pr_err("error: bad poison: %#x/%#x\n",
192 elb->poison1, elb->poison2);
193 return -EINVAL;
194 }
195 return 0;
196 }
197
cmp(void * priv,struct list_head * a,struct list_head * b)198 static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
199 {
200 struct debug_el *ela, *elb;
201
202 ela = container_of(a, struct debug_el, list);
203 elb = container_of(b, struct debug_el, list);
204
205 check(ela, elb);
206 return ela->value - elb->value;
207 }
208
list_sort_test(void)209 static int __init list_sort_test(void)
210 {
211 int i, count = 1, err = -ENOMEM;
212 struct debug_el *el;
213 struct list_head *cur;
214 LIST_HEAD(head);
215
216 pr_debug("start testing list_sort()\n");
217
218 elts = kcalloc(TEST_LIST_LEN, sizeof(*elts), GFP_KERNEL);
219 if (!elts) {
220 pr_err("error: cannot allocate memory\n");
221 return err;
222 }
223
224 for (i = 0; i < TEST_LIST_LEN; i++) {
225 el = kmalloc(sizeof(*el), GFP_KERNEL);
226 if (!el) {
227 pr_err("error: cannot allocate memory\n");
228 goto exit;
229 }
230 /* force some equivalencies */
231 el->value = prandom_u32() % (TEST_LIST_LEN / 3);
232 el->serial = i;
233 el->poison1 = TEST_POISON1;
234 el->poison2 = TEST_POISON2;
235 elts[i] = el;
236 list_add_tail(&el->list, &head);
237 }
238
239 list_sort(NULL, &head, cmp);
240
241 err = -EINVAL;
242 for (cur = head.next; cur->next != &head; cur = cur->next) {
243 struct debug_el *el1;
244 int cmp_result;
245
246 if (cur->next->prev != cur) {
247 pr_err("error: list is corrupted\n");
248 goto exit;
249 }
250
251 cmp_result = cmp(NULL, cur, cur->next);
252 if (cmp_result > 0) {
253 pr_err("error: list is not sorted\n");
254 goto exit;
255 }
256
257 el = container_of(cur, struct debug_el, list);
258 el1 = container_of(cur->next, struct debug_el, list);
259 if (cmp_result == 0 && el->serial >= el1->serial) {
260 pr_err("error: order of equivalent elements not "
261 "preserved\n");
262 goto exit;
263 }
264
265 if (check(el, el1)) {
266 pr_err("error: element check failed\n");
267 goto exit;
268 }
269 count++;
270 }
271 if (head.prev != cur) {
272 pr_err("error: list is corrupted\n");
273 goto exit;
274 }
275
276
277 if (count != TEST_LIST_LEN) {
278 pr_err("error: bad list length %d", count);
279 goto exit;
280 }
281
282 err = 0;
283 exit:
284 for (i = 0; i < TEST_LIST_LEN; i++)
285 kfree(elts[i]);
286 kfree(elts);
287 return err;
288 }
289 module_init(list_sort_test);
290 #endif /* CONFIG_TEST_LIST_SORT */
291