linux-kernel - Re: [PATCH v1 2/2] mm/ksm: Test case for prctl fork/exec workflow

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Date:   Wed, 20 Sep 2023 11:57:27 -0700
From:   Stefan Roesch <shr@...kernel.io>
To:     David Hildenbrand <david@...hat.com>
Cc:     kernel-team@...com, akpm@...ux-foundation.org, hannes@...xchg.org,
        riel@...riel.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 2/2] mm/ksm: Test case for prctl fork/exec workflow


David Hildenbrand <david@...hat.com> writes:

> On 19.09.23 22:51, Stefan Roesch wrote:
>> This adds a new test case to the ksm functional tests to make sure that
>> the KSM setting is inherited by the child process when doing a
>> fork/exec.
>> Signed-off-by: Stefan Roesch <shr@...kernel.io>
>> ---
>>   tools/testing/selftests/mm/Makefile           |  2 +
>>   .../selftests/mm/ksm_fork_exec_child.c        |  9 ++++
>>   .../selftests/mm/ksm_functional_tests.c       | 50 ++++++++++++++++++-
>>   3 files changed, 60 insertions(+), 1 deletion(-)
>>   create mode 100644 tools/testing/selftests/mm/ksm_fork_exec_child.c
>> diff --git a/tools/testing/selftests/mm/Makefile
>> b/tools/testing/selftests/mm/Makefile
>> index 6a9fc5693145..9ab6aa402544 100644
>> --- a/tools/testing/selftests/mm/Makefile
>> +++ b/tools/testing/selftests/mm/Makefile
>> @@ -73,6 +73,8 @@ ifneq ($(ARCH),arm64)
>>   TEST_GEN_PROGS += soft-dirty
>>   endif
>>   +TEST_GEN_PROGS += ksm_fork_exec_child
>
> It's not a test itself, so it shouldn't be run when running all tests. See
> below.
>
>> +
>>   ifeq ($(ARCH),x86_64)
>>   CAN_BUILD_I386 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_32bit_program.c -m32)
>>   CAN_BUILD_X86_64 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_64bit_program.c)
>> diff --git a/tools/testing/selftests/mm/ksm_fork_exec_child.c b/tools/testing/selftests/mm/ksm_fork_exec_child.c
>> new file mode 100644
>> index 000000000000..298439f0d55f
>> --- /dev/null
>> +++ b/tools/testing/selftests/mm/ksm_fork_exec_child.c
>> @@ -0,0 +1,9 @@
>> +#include <sys/prctl.h>
>> +#include <stdlib.h>
>> +
>> +int main()
>> +{
>> +	/* Test if KSM is enabled for the process. */
>> +	int ksm = prctl(68, 0, 0, 0, 0);
>
> Can we use the define from a header? (PR_SET_MEMORY_MERGE)
>

I changed it.

> I was wondering if we could simply exec() ourself (same binary), but pass a
> special cmdline argument. Then you don't have to build a separate binary.
>

I'm execing the same executable with an additional parameter.

> Just special-case in main() on that argument and perform this check.
>

I added a check in main and invoke a new function for the child.

>> +	exit(ksm == 1 ? 0 : 1);
>> +}
>> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
>> index 901e950f9138..4dc0bb522c07 100644
>> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
>> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
>> @@ -479,6 +479,53 @@ static void test_prctl_fork(void)
>>   	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
>>   }
>>   +static void test_prctl_fork_exec(void)
>> +{
>> +	int ret, status;
>> +	pid_t child_pid;
>> +
>> +	ksft_print_msg("[RUN] %s\n", __func__);
>> +
>> +	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
>> +	if (ret < 0 && errno == EINVAL) {
>> +		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
>> +		return;
>> +	} else if (ret) {
>> +		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
>> +		return;
>> +	}
>> +
>> +	child_pid = fork();
>> +	if (child_pid == -1) {
>> +		ksft_test_result_skip("fork() failed\n");
>> +		return;
>> +	} else if (child_pid == 0) {
>> +		char *filename = "./ksm_fork_exec_child";
>> +		char *argv_for_program[] = { filename, NULL };
>> +
>> +		execv(filename, argv_for_program);;
>
> s/;;/;/
>

Fixed.

> Add a return; so you can simplify the code below (no need for the "else")
>

Done.


>> +	} else {
>> +		if (waitpid(child_pid, &status, 0) > 0) {
>> +			if (WIFEXITED(status)) {
>> +				status = WEXITSTATUS(status);
>> +				if (status) {
>> +					ksft_test_result_fail("KSM not enabled\n");
>> +					return;
>> +				}
>> +
>> +			} else {
>> +				ksft_test_result_fail("program didn't terminate normally\n");
>> +				return;
>> +			}
>> +		} else {
>> +			ksft_test_result_fail("waitpid() failed\n");
>> +			return;
>> +		}
>> +	}
>> +
>> +	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
>
> It's probably the cleanest to disable PR_SET_MEMORY_MERGE again when returning
> form this function, so the other tests have a clean slate.

In the next version it is disabled at the end.