1 // SPDX-License-Identifier: GPL-2.0
2 #include <stdio.h>
3 #include <sys/mman.h>
4 #include <unistd.h>
5
6 #include "utils.h"
7
8 /* This must match the huge page & THP size */
9 #define SIZE (16 * 1024 * 1024)
10
11 static int test_body(void)
12 {
13 void *addr;
14 char *p;
15
16 addr = (void *)0xa0000000;
17
18 p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
19 MAP_HUGETLB | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
20 if (p != MAP_FAILED) {
21 /*
22 * Typically the mmap will fail because no huge pages are
23 * allocated on the system. But if there are huge pages
24 * allocated the mmap will succeed. That's fine too, we just
25 * munmap here before continuing. munmap() length of
26 * MAP_HUGETLB memory must be hugepage aligned.
27 */
28 if (munmap(addr, SIZE)) {
29 perror("munmap");
30 return 1;
31 }
32 }
33
34 p = mmap(addr, SIZE, PROT_READ | PROT_WRITE,
35 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
36 if (p == MAP_FAILED) {
37 printf("Mapping failed @ %p\n", addr);
38 perror("mmap");
39 return 1;
40 }
41
42 /*
43 * Either a user or kernel access is sufficient to trigger the bug.
44 * A kernel access is easier to spot & debug, as it will trigger the
45 * softlockup or RCU stall detectors, and when the system is kicked
46 * into xmon we get a backtrace in the kernel.
47 *
48 * A good option is:
49 * getcwd(p, SIZE);
50 *
51 * For the purposes of this testcase it's preferable to spin in
52 * userspace, so the harness can kill us if we get stuck. That way we
53 * see a test failure rather than a dead system.
54 */
55 *p = 0xf;
56
57 munmap(addr, SIZE);
58
59 return 0;
60 }
61
62 static int test_main(void)
63 {
64 int i;
65
66 /* 10,000 because it's a "bunch", and completes reasonably quickly */
67 for (i = 0; i < 10000; i++)
68 if (test_body())
69 return 1;
70
71 return 0;
72 }
73
74 int main(void)
75 {
76 return test_harness(test_main, "hugetlb_vs_thp");
77 }