projects/linux·blob uaccess-cleanups · refs

353 lines · 7.8 KiB

1// SPDX-License-Identifier: LGPL-2.1
2#define _GNU_SOURCE
3#include <assert.h>
4#include <pthread.h>
5#include <sched.h>
6#include <stdint.h>
7#include <stdio.h>
8#include <stdlib.h>
9#include <string.h>
10#include <stddef.h>
11
12#include "kselftest.h"
13#include "rseq.h"
14
15#ifdef BUILDOPT_RSEQ_PERCPU_MM_CID
16# define RSEQ_PERCPU RSEQ_PERCPU_MM_CID
17static
18int get_current_cpu_id(void)
19{
20 return rseq_current_mm_cid();
21}
22static
23bool rseq_validate_cpu_id(void)
24{
25 return rseq_mm_cid_available();
26}
27static
28bool rseq_use_cpu_index(void)
29{
30 return false; /* Use mm_cid */
31}
32#else
33# define RSEQ_PERCPU RSEQ_PERCPU_CPU_ID
34static
35int get_current_cpu_id(void)
36{
37 return rseq_cpu_start();
38}
39static
40bool rseq_validate_cpu_id(void)
41{
42 return rseq_current_cpu_raw() >= 0;
43}
44static
45bool rseq_use_cpu_index(void)
46{
47 return true; /* Use cpu_id as index. */
48}
49#endif
50
51struct percpu_lock_entry {
52 intptr_t v;
53} __attribute__((aligned(128)));
54
55struct percpu_lock {
56 struct percpu_lock_entry c[CPU_SETSIZE];
57};
58
59struct test_data_entry {
60 intptr_t count;
61} __attribute__((aligned(128)));
62
63struct spinlock_test_data {
64 struct percpu_lock lock;
65 struct test_data_entry c[CPU_SETSIZE];
66 int reps;
67};
68
69struct percpu_list_node {
70 intptr_t data;
71 struct percpu_list_node *next;
72};
73
74struct percpu_list_entry {
75 struct percpu_list_node *head;
76} __attribute__((aligned(128)));
77
78struct percpu_list {
79 struct percpu_list_entry c[CPU_SETSIZE];
80};
81
82/* A simple percpu spinlock. Returns the cpu lock was acquired on. */
83int rseq_this_cpu_lock(struct percpu_lock *lock)
84{
85 int cpu;
86
87 for (;;) {
88 int ret;
89
90 cpu = get_current_cpu_id();
91 ret = rseq_cmpeqv_storev(RSEQ_MO_RELAXED, RSEQ_PERCPU,
92 &lock->c[cpu].v, 0, 1, cpu);
93 if (rseq_likely(!ret))
94 break;
95 /* Retry if comparison fails or rseq aborts. */
96 }
97 /*
98 * Acquire semantic when taking lock after control dependency.
99 * Matches rseq_smp_store_release().
100 */
101 rseq_smp_acquire__after_ctrl_dep();
102 return cpu;
103}
104
105void rseq_percpu_unlock(struct percpu_lock *lock, int cpu)
106{
107 assert(lock->c[cpu].v == 1);
108 /*
109 * Release lock, with release semantic. Matches
110 * rseq_smp_acquire__after_ctrl_dep().
111 */
112 rseq_smp_store_release(&lock->c[cpu].v, 0);
113}
114
115void *test_percpu_spinlock_thread(void *arg)
116{
117 struct spinlock_test_data *data = arg;
118 int i, cpu;
119
120 if (rseq_register_current_thread()) {
121 fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
122 errno, strerror(errno));
123 abort();
124 }
125 for (i = 0; i < data->reps; i++) {
126 cpu = rseq_this_cpu_lock(&data->lock);
127 data->c[cpu].count++;
128 rseq_percpu_unlock(&data->lock, cpu);
129 }
130 if (rseq_unregister_current_thread()) {
131 fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
132 errno, strerror(errno));
133 abort();
134 }
135
136 return NULL;
137}
138
139/*
140 * A simple test which implements a sharded counter using a per-cpu
141 * lock. Obviously real applications might prefer to simply use a
142 * per-cpu increment; however, this is reasonable for a test and the
143 * lock can be extended to synchronize more complicated operations.
144 */
145void test_percpu_spinlock(void)
146{
147 const int num_threads = 200;
148 int i;
149 uint64_t sum;
150 pthread_t test_threads[num_threads];
151 struct spinlock_test_data data;
152
153 memset(&data, 0, sizeof(data));
154 data.reps = 5000;
155
156 for (i = 0; i < num_threads; i++)
157 pthread_create(&test_threads[i], NULL,
158 test_percpu_spinlock_thread, &data);
159
160 for (i = 0; i < num_threads; i++)
161 pthread_join(test_threads[i], NULL);
162
163 sum = 0;
164 for (i = 0; i < CPU_SETSIZE; i++)
165 sum += data.c[i].count;
166
167 assert(sum == (uint64_t)data.reps * num_threads);
168}
169
170void this_cpu_list_push(struct percpu_list *list,
171 struct percpu_list_node *node,
172 int *_cpu)
173{
174 int cpu;
175
176 for (;;) {
177 intptr_t *targetptr, newval, expect;
178 int ret;
179
180 cpu = get_current_cpu_id();
181 /* Load list->c[cpu].head with single-copy atomicity. */
182 expect = (intptr_t)RSEQ_READ_ONCE(list->c[cpu].head);
183 newval = (intptr_t)node;
184 targetptr = (intptr_t *)&list->c[cpu].head;
185 node->next = (struct percpu_list_node *)expect;
186 ret = rseq_cmpeqv_storev(RSEQ_MO_RELAXED, RSEQ_PERCPU,
187 targetptr, expect, newval, cpu);
188 if (rseq_likely(!ret))
189 break;
190 /* Retry if comparison fails or rseq aborts. */
191 }
192 if (_cpu)
193 *_cpu = cpu;
194}
195
196/*
197 * Unlike a traditional lock-less linked list; the availability of a
198 * rseq primitive allows us to implement pop without concerns over
199 * ABA-type races.
200 */
201struct percpu_list_node *this_cpu_list_pop(struct percpu_list *list,
202 int *_cpu)
203{
204 for (;;) {
205 struct percpu_list_node *head;
206 intptr_t *targetptr, expectnot, *load;
207 long offset;
208 int ret, cpu;
209
210 cpu = get_current_cpu_id();
211 targetptr = (intptr_t *)&list->c[cpu].head;
212 expectnot = (intptr_t)NULL;
213 offset = offsetof(struct percpu_list_node, next);
214 load = (intptr_t *)&head;
215 ret = rseq_cmpnev_storeoffp_load(RSEQ_MO_RELAXED, RSEQ_PERCPU,
216 targetptr, expectnot,
217 offset, load, cpu);
218 if (rseq_likely(!ret)) {
219 if (_cpu)
220 *_cpu = cpu;
221 return head;
222 }
223 if (ret > 0)
224 return NULL;
225 /* Retry if rseq aborts. */
226 }
227}
228
229/*
230 * __percpu_list_pop is not safe against concurrent accesses. Should
231 * only be used on lists that are not concurrently modified.
232 */
233struct percpu_list_node *__percpu_list_pop(struct percpu_list *list, int cpu)
234{
235 struct percpu_list_node *node;
236
237 node = list->c[cpu].head;
238 if (!node)
239 return NULL;
240 list->c[cpu].head = node->next;
241 return node;
242}
243
244void *test_percpu_list_thread(void *arg)
245{
246 int i;
247 struct percpu_list *list = (struct percpu_list *)arg;
248
249 if (rseq_register_current_thread()) {
250 fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
251 errno, strerror(errno));
252 abort();
253 }
254
255 for (i = 0; i < 100000; i++) {
256 struct percpu_list_node *node;
257
258 node = this_cpu_list_pop(list, NULL);
259 sched_yield(); /* encourage shuffling */
260 if (node)
261 this_cpu_list_push(list, node, NULL);
262 }
263
264 if (rseq_unregister_current_thread()) {
265 fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
266 errno, strerror(errno));
267 abort();
268 }
269
270 return NULL;
271}
272
273/* Simultaneous modification to a per-cpu linked list from many threads. */
274void test_percpu_list(void)
275{
276 int i, j;
277 uint64_t sum = 0, expected_sum = 0;
278 struct percpu_list list;
279 pthread_t test_threads[200];
280 cpu_set_t allowed_cpus;
281
282 memset(&list, 0, sizeof(list));
283
284 /* Generate list entries for every usable cpu. */
285 sched_getaffinity(0, sizeof(allowed_cpus), &allowed_cpus);
286 for (i = 0; i < CPU_SETSIZE; i++) {
287 if (rseq_use_cpu_index() && !CPU_ISSET(i, &allowed_cpus))
288 continue;
289 for (j = 1; j <= 100; j++) {
290 struct percpu_list_node *node;
291
292 expected_sum += j;
293
294 node = malloc(sizeof(*node));
295 assert(node);
296 node->data = j;
297 node->next = list.c[i].head;
298 list.c[i].head = node;
299 }
300 }
301
302 for (i = 0; i < 200; i++)
303 pthread_create(&test_threads[i], NULL,
304 test_percpu_list_thread, &list);
305
306 for (i = 0; i < 200; i++)
307 pthread_join(test_threads[i], NULL);
308
309 for (i = 0; i < CPU_SETSIZE; i++) {
310 struct percpu_list_node *node;
311
312 if (rseq_use_cpu_index() && !CPU_ISSET(i, &allowed_cpus))
313 continue;
314
315 while ((node = __percpu_list_pop(&list, i))) {
316 sum += node->data;
317 free(node);
318 }
319 }
320
321 /*
322 * All entries should now be accounted for (unless some external
323 * actor is interfering with our allowed affinity while this
324 * test is running).
325 */
326 assert(sum == expected_sum);
327}
328
329int main(int argc, char **argv)
330{
331 if (rseq_register_current_thread()) {
332 fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
333 errno, strerror(errno));
334 goto error;
335 }
336 if (!rseq_validate_cpu_id()) {
337 fprintf(stderr, "Error: cpu id getter unavailable\n");
338 goto error;
339 }
340 printf("spinlock\n");
341 test_percpu_spinlock();
342 printf("percpu_list\n");
343 test_percpu_list();
344 if (rseq_unregister_current_thread()) {
345 fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
346 errno, strerror(errno));
347 goto error;
348 }
349 return 0;
350
351error:
352 return -1;
353}