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

From: Oleg Nesterov <oleg@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: 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,
	Dmitry Vyukov <dvyukov@google.com>,
	kasan-dev@googlegroups.com, Edward Liaw <edliaw@google.com>,
	Carlos Llamas <cmllamas@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v6 1/2] posix-timers: Prefer delivery of signals to the current thread
Date: Wed, 3 Apr 2024 17:03:43 +0200	[thread overview]
Message-ID: <20240403150343.GC31764@redhat.com> (raw)
In-Reply-To: <874jcid3f6.ffs@tglx>

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.