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 
test_body(void)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 
test_main(void)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 
main(void)74 int main(void)
75 {
76 	return test_harness(test_main, "hugetlb_vs_thp");
77 }
78