Commit 116d5730 authored by Breno Leitao's avatar Breno Leitao Committed by Andrew Morton
Browse files

selftests/mm: add a new test for madv and hugetlb 

Create a selftest that exercises the race between page faults and
madvise(MADV_DONTNEED) in the same huge page. Do it by running two
threads that touches the huge page and madvise(MADV_DONTNEED) at the same
time.

In case of a SIGBUS coming at pagefault, the test should fail, since we
hit the bug.

The test doesn't have a signal handler, and if it fails, it fails like
the following

  ----------------------------------
  running ./hugetlb_fault_after_madv
  ----------------------------------
  ./run_vmtests.sh: line 186: 595563 Bus error    (core dumped) "$@"
  [FAIL]

This selftest goes together with the fix of the bug[1] itself.

[1] https://lore.kernel.org/all/20231001005659.2185316-1-riel@surriel.com/#r

Link: https://lkml.kernel.org/r/20231005163922.87568-3-leitao@debian.org


Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Reviewed-by: default avatarRik van Riel <riel@surriel.com>
Tested-by: default avatarRik van Riel <riel@surriel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent c8b90731

tools/testing/selftests/mm/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -69,6 +69,7 @@ TEST_GEN_FILES += split_huge_page_test 
TEST_GEN_FILES += ksm_tests

TEST_GEN_FILES += ksm_functional_tests

TEST_GEN_FILES += mdwe_test

TEST_GEN_FILES += hugetlb_fault_after_madv



ifneq ($(ARCH),arm64)

TEST_GEN_PROGS += soft-dirty

tools/testing/selftests/mm/hugetlb_fault_after_madv.c

0 → 100644
+73 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#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)

{

	char *ptr = (char *)huge_ptr;



	for (int i = 0; i < INLOOP_ITER; i++)

		ptr[0] = '.';



	return NULL;

}



void *madv(void *unused)

{

	usleep(rand() % 10);



	for (int i = 0; i < INLOOP_ITER; i++)

		madvise(huge_ptr, MMAP_SIZE, MADV_DONTNEED);



	return NULL;

}



int main(void)

{

	unsigned long free_hugepages;

	pthread_t thread1, thread2;

	/*

	 * On kernel 6.4, we are able to reproduce the problem with ~1000

	 * interactions

	 */

	int max = 10000;



	srand(getpid());



	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");



		pthread_create(&thread1, NULL, madv, NULL);

		pthread_create(&thread2, NULL, touch, NULL);



		pthread_join(thread1, NULL);

		pthread_join(thread2, NULL);

		munmap(huge_ptr, MMAP_SIZE);

	}



	return KSFT_PASS;

}

tools/testing/selftests/mm/run_vmtests.sh

+4 −0
Original line number Diff line number Diff line
@@ -223,6 +223,10 @@ CATEGORY="hugetlb" run_test ./hugepage-mremap 
CATEGORY="hugetlb" run_test ./hugepage-vmemmap

CATEGORY="hugetlb" run_test ./hugetlb-madvise



# For this test, we need one and just one huge page

echo 1 > /proc/sys/vm/nr_hugepages

CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv



if test_selected "hugetlb"; then

	echo "NOTE: These hugetlb tests provide minimal coverage.  Use"

	echo "      https://github.com/libhugetlbfs/libhugetlbfs.git for"