linux-kernel - Re: [PATCH v6 1/2] posix-timers: Prefer delivery of signals to the current thread

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Date: Wed, 3 Apr 2024 17:03:43 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: John Stultz <jstultz@...gle.com>, Marco Elver <elver@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
	Edward Liaw <edliaw@...gle.com>,
	Carlos Llamas <cmllamas@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v6 1/2] posix-timers: Prefer delivery of signals to the
 current thread

On 04/03, Thomas Gleixner wrote:
>
> The test if fragile as hell as there is absolutely no guarantee that the
> signal target distribution is as expected. The expectation is based on a
> statistical assumption which does not really hold.

Agreed. I too never liked this test-case.

I forgot everything about this patch and test-case, I can't really read
your patch right now (sorry), so I am sure I missed something, but

>  static void *distribution_thread(void *arg)
>  {
> -	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
> -	return NULL;
> +	while (__atomic_load_n(&remain, __ATOMIC_RELAXED) && !done) {
> +		if (got_signal)
> +			usleep(10);
> +	}
> +
> +	return (void *)got_signal;
>  }

Why distribution_thread() can't simply exit if got_signal != 0 ?

See https://lore.kernel.org/all/20230128195641.GA14906@redhat.com/

Oleg.