1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * A test case that must run on a system with one and only one huge page available.
4 * # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
5 *
6 * During setup, the test allocates the only available page, and starts three threads:
7 * - thread1:
8 * * madvise(MADV_DONTNEED) on the allocated huge page
9 * - thread 2:
10 * * Write to the allocated huge page
11 * - thread 3:
12 * * Try to allocated an extra huge page (which must not available)
13 *
14 * The test fails if thread3 is able to allocate a page.
15 *
16 * Touching the first page after thread3's allocation will raise a SIGBUS
17 *
18 * Author: Breno Leitao <leitao@debian.org>
19 */
20 #include <pthread.h>
21 #include <stdio.h>
22 #include <stdlib.h>
23 #include <sys/mman.h>
24 #include <sys/types.h>
25 #include <unistd.h>
26
27 #include "vm_util.h"
28 #include "../kselftest.h"
29
30 #define INLOOP_ITER 100
31
32 size_t mmap_size;
33 char *huge_ptr;
34
35 /* Touch the memory while it is being madvised() */
36 void *touch(void *unused)
37 {
38 for (int i = 0; i < INLOOP_ITER; i++)
39 huge_ptr[0] = '.';
40
41 return NULL;
42 }
43
44 void *madv(void *unused)
45 {
46 for (int i = 0; i < INLOOP_ITER; i++)
47 madvise(huge_ptr, mmap_size, MADV_DONTNEED);
48
49 return NULL;
50 }
51
52 /*
53 * We got here, and there must be no huge page available for mapping
54 * The other hugepage should be flipping from used <-> reserved, because
55 * of madvise(DONTNEED).
56 */
57 void *map_extra(void *unused)
58 {
59 void *ptr;
60
61 for (int i = 0; i < INLOOP_ITER; i++) {
62 ptr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
63 MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
64 -1, 0);
65
66 if ((long)ptr != -1) {
67 /* Touching the other page now will cause a SIGBUG
68 * huge_ptr[0] = '1';
69 */
70 return ptr;
71 }
72 }
73
74 return NULL;
75 }
76
77 int main(void)
78 {
79 pthread_t thread1, thread2, thread3;
80 unsigned long free_hugepages;
81 void *ret;
82
83 /*
84 * On kernel 6.7, we are able to reproduce the problem with ~10
85 * interactions
86 */
87 int max = 10;
88
89 free_hugepages = get_free_hugepages();
90
91 if (free_hugepages != 1) {
92 ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
93 free_hugepages);
94 }
95
96 mmap_size = default_huge_page_size();
97
98 while (max--) {
99 huge_ptr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
100 MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
101 -1, 0);
102
103 if ((unsigned long)huge_ptr == -1) {
104 ksft_test_result_fail("Failed to allocate huge page\n");
105 return KSFT_FAIL;
106 }
107
108 pthread_create(&thread1, NULL, madv, NULL);
109 pthread_create(&thread2, NULL, touch, NULL);
110 pthread_create(&thread3, NULL, map_extra, NULL);
111
112 pthread_join(thread1, NULL);
113 pthread_join(thread2, NULL);
114 pthread_join(thread3, &ret);
115
116 if (ret) {
117 ksft_test_result_fail("Unexpected huge page allocation\n");
118 return KSFT_FAIL;
119 }
120
121 /* Unmap and restart */
122 munmap(huge_ptr, mmap_size);
123 }
124
125 return KSFT_PASS;
126 }
127
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