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Date: Tue, 9 Apr 2024 13:10:52 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Dmitry Vyukov <dvyukov@google.com>, John Stultz <jstultz@google.com>,
	Marco Elver <elver@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
	kasan-dev@googlegroups.com, Edward Liaw <edliaw@google.com>,
	Carlos Llamas <cmllamas@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] selftests/timers/posix_timers: reimplement
 check_timer_distribution()
Message-ID: <20240409111051.GB29396@redhat.com>
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On 04/09, Thomas Gleixner wrote:
>
> The discussion started about running new tests on older kernels. As this
> is a feature and not a bug fix that obviously fails on older kernels.

OK, I see... please see below.

> So something like the uncompiled below should work.

Hmm... this patch doesn't apply to Linus's tree...

It seems that this is because in your tree check_timer_distribution() does

	if (timer_delete(id)) {
		ksft_perror("Can't delete timer");
		return 0;
	}

while in Linus's tree it returns -1 if timer_delete() fails. Nevermind.

Thomas, I am almost shy to continue this discussion and waste your time ;)
But ...

> +static bool check_kernel_version(unsigned int min_major, unsigned int min_minor)
> +{
> +	unsigned int major, minor;
> +	struct utsname info;
> +
> +	uname(&info);
> +	if (sscanf(info.release, "%u.%u.", &major, &minor) != 2)
> +		ksft_exit_fail();
> +	return major > min_major || (major == min_major && minor >= min_minor);
> +}

this looks useful regardless. Perhaps it should be moved into
tools/testing/selftests/kselftest.h as ksft_ck_kernel_version() ?

> +static int check_timer_distribution(void)
> +{
> +	const char *errmsg;
> +
> +	if (!check_kernel_version(6, 3)) {
> +		ksft_test_result_skip("check signal distribution (old kernel)\n");
>  		return 0;

..

> +	ksft_test_result(!ctd_failed, "check signal distribution\n");

Perhaps

	if (!ctd_failed)
		ksft_test_result_pass("check signal distribution\n");
	else if (check_kernel_version(6, 3))
		ksft_test_result_fail("check signal distribution\n");
	else
		ksft_test_result_skip("check signal distribution (old kernel)\n");

makes more sense?

This way it can be used on the older kernels with bcb7ee79029d backported.

Oleg.