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  3. [PATCH v2 0/3] mm/ksm: Fix incorrect accounting of KSM counters during fork.
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[PATCH v2 2/3] selftests/mm: Added fork inheritance test for ksm_merging_pages counter

Donet Tom posted 3 patches 4 months, 3 weeks ago
There is a newer version of this series
[PATCH v2 2/3] selftests/mm: Added fork inheritance test for ksm_merging_pages counter
Posted by Donet Tom 4 months, 3 weeks ago 
Added 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.

Signed-off-by: Donet Tom <donettom@linux.ibm.com>
---
 .../selftests/mm/ksm_functional_tests.c       | 42 ++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index 712f43c87736..645cefba2126 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -602,6 +602,45 @@ 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");
+		return;
+	}
+
+	if (waitpid(child_pid, &status, 0) < 0) {
+		ksft_test_result_fail("waitpid() failed\n");
+		return;
+	}
+
+	status = WEXITSTATUS(status);
+	if (status) {
+		ksft_test_result_fail("ksm_merging_page in child: %d\n", status);
+		return;
+	}
+
+	ksft_test_result_pass("ksm_merging_pages is not inherited after fork\n");
+
+	ksm_stop();
+	munmap(map, size);
+}
+
 static void init_global_file_handles(void)
 {
 	mem_fd = open("/proc/self/mem", O_RDWR);
@@ -620,7 +659,7 @@ 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 +691,7 @@ 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)
-- 
2.51.0
Re: [PATCH v2 2/3] selftests/mm: Added fork inheritance test for ksm_merging_pages counter
Posted by David Hildenbrand 4 months, 3 weeks ago 
On 15.09.25 17:03, Donet Tom wrote:
> Added 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.
> 
> Signed-off-by: Donet Tom <donettom@linux.ibm.com>
> ---
>   .../selftests/mm/ksm_functional_tests.c       | 42 ++++++++++++++++++-
>   1 file changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 712f43c87736..645cefba2126 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -602,6 +602,45 @@ 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");
> +		return;

Probably
	goto out;

in all these fail cases

> +	}
> +
> +	if (waitpid(child_pid, &status, 0) < 0) {
> +		ksft_test_result_fail("waitpid() failed\n");
> +		return;
> +	}
> +
> +	status = WEXITSTATUS(status);
> +	if (status) {
> +		ksft_test_result_fail("ksm_merging_page in child: %d\n", status);
> +		return;
> +	}
> +
> +	ksft_test_result_pass("ksm_merging_pages is not inherited after fork\n");
> +

And have

	out:

here

With that:

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb
Re: [PATCH v2 2/3] selftests/mm: Added fork inheritance test for ksm_merging_pages counter
Posted by Donet Tom 4 months, 3 weeks ago 
On 9/17/25 6:45 PM, David Hildenbrand wrote:
> On 15.09.25 17:03, Donet Tom wrote:
>> Added 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.
>>
>> Signed-off-by: Donet Tom <donettom@linux.ibm.com>
>> ---
>>   .../selftests/mm/ksm_functional_tests.c       | 42 ++++++++++++++++++-
>>   1 file changed, 41 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c 
>> b/tools/testing/selftests/mm/ksm_functional_tests.c
>> index 712f43c87736..645cefba2126 100644
>> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
>> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
>> @@ -602,6 +602,45 @@ 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");
>> +        return;
>
> Probably
>     goto out;
>
> in all these fail cases
>
>> +    }
>> +
>> +    if (waitpid(child_pid, &status, 0) < 0) {
>> +        ksft_test_result_fail("waitpid() failed\n");
>> +        return;
>> +    }
>> +
>> +    status = WEXITSTATUS(status);
>> +    if (status) {
>> +        ksft_test_result_fail("ksm_merging_page in child: %d\n", 
>> status);
>> +        return;
>> +    }
>> +
>> +    ksft_test_result_pass("ksm_merging_pages is not inherited after 
>> fork\n");
>> +
>
> And have
>
>     out:
>
> here


Sure, I will send a v3 with this change.


>
> With that:
>
> Acked-by: David Hildenbrand <david@redhat.com>
>

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