droppable.c

 1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Copyright (C) 2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 4 */
 5
 6#include <assert.h>
 7#include <stdbool.h>
 8#include <stdint.h>
 9#include <stdio.h>
10#include <stdlib.h>
11#include <unistd.h>
12#include <signal.h>
13#include <sys/mman.h>
14#include <linux/mman.h>
15
16#include "kselftest.h"
17
18int main(int argc, char *argv[])
19{
20	size_t alloc_size = 134217728;
21	size_t page_size = getpagesize();
22	void *alloc;
23	pid_t child;
24
25	ksft_print_header();
26	ksft_set_plan(1);
27
28	alloc = mmap(0, alloc_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_DROPPABLE, -1, 0);
29	assert(alloc != MAP_FAILED);
30	memset(alloc, 'A', alloc_size);
31	for (size_t i = 0; i < alloc_size; i += page_size)
32		assert(*(uint8_t *)(alloc + i));
33
34	child = fork();
35	assert(child >= 0);
36	if (!child) {
37		for (;;)
38			*(char *)malloc(page_size) = 'B';
39	}
40
41	for (bool done = false; !done;) {
42		for (size_t i = 0; i < alloc_size; i += page_size) {
43			if (!*(uint8_t *)(alloc + i)) {
44				done = true;
45				break;
46			}
47		}
48	}
49	kill(child, SIGTERM);
50
51	ksft_test_result_pass("MAP_DROPPABLE: PASS\n");
52	exit(KSFT_PASS);
53}