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selftests/mm: add fork inheritance test for ksm_merging_pages counter

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Add a new selftest to verify whether the `ksm_merging_pages` counter in
`mm_struct` is not inherited by a child process after fork.  This helps
ensure correctness of KSM accounting across process creation.

Link: https://lkml.kernel.org/r/e7bb17d374133bd31a3e423aa9e46e1122e74971.1758648700.git.donettom@linux.ibm.com
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Aboorva Devarajan <aboorvad@linux.ibm.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Donet Tom 2025-09-24 00:17:00 +05:30 committed by Andrew Morton
parent 4d6fc29f36
commit 08ff89b565
1 changed files with 42 additions and 1 deletions
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43
tools/testing/selftests/mm/ksm_functional_tests.c
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@ -602,6 +602,46 @@ static void test_prot_none(void)
munmap(map, size);
}
static void test_fork_ksm_merging_page_count(void)
{
const unsigned int size = 2 * MiB;
char *map;
pid_t child_pid;
int status;
ksft_print_msg("[RUN] %s\n", __func__);
map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, KSM_MERGE_MADVISE);
if (map == MAP_FAILED)
return;
child_pid = fork();
if (!child_pid) {
init_global_file_handles();
exit(ksm_get_self_merging_pages());
} else if (child_pid < 0) {
ksft_test_result_fail("fork() failed\n");
goto unmap;
}
if (waitpid(child_pid, &status, 0) < 0) {
ksft_test_result_fail("waitpid() failed\n");
goto unmap;
}
status = WEXITSTATUS(status);
if (status) {
ksft_test_result_fail("ksm_merging_page in child: %d\n", status);
goto unmap;
}
ksft_test_result_pass("ksm_merging_pages is not inherited after fork\n");
unmap:
ksm_stop();
munmap(map, size);
}
static void init_global_file_handles(void)
{
mem_fd = open("/proc/self/mem", O_RDWR);
@ -620,7 +660,7 @@ static void init_global_file_handles(void)
int main(int argc, char **argv)
{
unsigned int tests = 8;
unsigned int tests = 9;
int err;
if (argc > 1 && !strcmp(argv[1], FORK_EXEC_CHILD_PRG_NAME)) {
@ -652,6 +692,7 @@ int main(int argc, char **argv)
test_prctl_fork();
test_prctl_fork_exec();
test_prctl_unmerge();
test_fork_ksm_merging_page_count();
err = ksft_get_fail_cnt();
if (err)