// 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 INLOOP_ITER 100

size_t mmap_size;
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);
        }

        mmap_size = default_huge_page_size();

        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_test_result_fail("Failed to allocate huge page\n");
                        return KSFT_FAIL;
                }

                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;
}