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

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Message-ID: <daf57da6-b22d-bdfb-c6f0-0ac07824ab72@redhat.com>
Date:   Wed, 20 Sep 2023 15:16:38 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Stefan Roesch <shr@...kernel.io>, kernel-team@...com
Cc:     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

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 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.

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

> +	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/;;/;/

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

> +	} 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.


-- 
Cheers,

David / dhildenb