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// SPDX-License-Identifier: GPL-2.0
/*
* A test case that must run on a system with one and only one huge page available.
* # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
*
* During setup, the test allocates the only available page, and starts three threads:
* - thread1:
* * madvise(MADV_DONTNEED) on the allocated huge page
* - thread 2:
* * Write to the allocated huge page
* - thread 3:
* * Try to allocated an extra huge page (which must not available)
*
* The test fails if thread3 is able to allocate a page.
*
* Touching the first page after thread3's allocation will raise a SIGBUS
*
* Author: Breno Leitao <leitao@debian.org>
*/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <unistd.h>
#include "vm_util.h"
#include "../kselftest.h"
#define MMAP_SIZE (1 << 21)
#define INLOOP_ITER 100
char *huge_ptr;
/* Touch the memory while it is being madvised() */
void *touch(void *unused)
{
for (int i = 0; i < INLOOP_ITER; i++)
huge_ptr[0] = '.';
return NULL;
}
void *madv(void *unused)
{
for (int i = 0; i < INLOOP_ITER; i++)
madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);
return NULL;
}
/*
* We got here, and there must be no huge page available for mapping
* The other hugepage should be flipping from used <-> reserved, because
* of madvise(DONTNEED).
*/
void *map_extra(void *unused)
{
void *ptr;
for (int i = 0; i < INLOOP_ITER; i++) {
ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
-1, 0);
if ((long)ptr != -1) {
/* Touching the other page now will cause a SIGBUG
* huge_ptr[0] = '1';
*/
return ptr;
}
}
return NULL;
}
int main(void)
{
pthread_t thread1, thread2, thread3;
unsigned long free_hugepages;
void *ret;
/*
* On kernel 6.7, we are able to reproduce the problem with ~10
* interactions
*/
int max = 10;
free_hugepages = get_free_hugepages();
if (free_hugepages != 1) {
ksft_exit_skip("This test needs one and only one page to execute. Got %lu\n",
free_hugepages);
}
while (max--) {
huge_ptr = mmap(NULL, MMAP_SIZE, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB,
-1, 0);
if ((unsigned long)huge_ptr == -1) {
ksft_exit_skip("Failed to allocated huge page\n");
return KSFT_SKIP;
}
pthread_create(&thread1, NULL, madv, NULL);
pthread_create(&thread2, NULL, touch, NULL);
pthread_create(&thread3, NULL, map_extra, NULL);
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
pthread_join(thread3, &ret);
if (ret) {
ksft_test_result_fail("Unexpected huge page allocation\n");
return KSFT_FAIL;
}
/* Unmap and restart */
munmap(huge_ptr, MMAP_SIZE);
}
return KSFT_PASS;
}
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