linux-kernel - Re: [PATCH v2 2/2] mm/ksm: Test case for prctl fork/exec workflow

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Date:   Thu, 21 Sep 2023 13:44:08 +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 v2 2/2] mm/ksm: Test case for prctl fork/exec workflow

On 20.09.23 21:01, 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>
> ---
>   .../selftests/mm/ksm_functional_tests.c       | 67 ++++++++++++++++++-
>   1 file changed, 66 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
> index 901e950f9138..40b86c9caf3a 100644
> --- a/tools/testing/selftests/mm/ksm_functional_tests.c
> +++ b/tools/testing/selftests/mm/ksm_functional_tests.c
> @@ -26,6 +26,7 @@
>   
>   #define KiB 1024u
>   #define MiB (1024 * KiB)
> +#define FORK_EXEC_CHILD_PRG_NAME "ksm_fork_exec_child"
>   
>   static int mem_fd;
>   static int ksm_fd;
> @@ -479,6 +480,65 @@ static void test_prctl_fork(void)
>   	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
>   }
>   
> +static int ksm_fork_exec_child(void)
> +{
> +	/* Test if KSM is enabled for the process. */
> +	int ksm = prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);
> +	return ksm == 1;

You can simply do "return prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0) == 1;"

Or maybe even "return prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);" and 
adjust the comparison below in the caller.

> +}
> +
> +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 *prg_name = "./ksm_functional_tests";
> +		char *argv_for_program[] = { prg_name, FORK_EXEC_CHILD_PRG_NAME };
> +

I'd simply have used the magic number "1" or so. But this works as well.

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb