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