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 11:16:12 -0700
From: John Stultz <jstultz@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Oleg Nesterov <oleg@...hat.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 Wed, Apr 3, 2024 at 9:32 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> Subject: selftests/timers/posix_timers: Make signal distribution test less fragile
> From: Thomas Gleixner <tglx@...utronix.de>
>
> The signal distribution test has a tendency to hang for a long time as the
> signal delivery is not really evenly distributed. In fact it might never be
> distributed across all threads ever in the way it is written.
>
> Address this by:
>
>    1) Adding a timeout which aborts the test
>
>    2) Letting the test threads exit once they got a signal instead of
>       running continuously. That ensures that the other threads will
>       have a chance to expire the timer and get the signal.
>
>    3) Adding a detection whether all signals arrvied at the main thread,
>       which allows to run the test on older kernels and emit 'SKIP'.
>
> While at it get rid of the pointless atomic operation on a the thread local
> variable in the signal handler.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Thanks for this, Thomas!

Just FYI: testing with 6.1, the test no longer hangs, but I don't see
the SKIP behavior. It just fails:
not ok 6 check signal distribution
# Totals: pass:5 fail:1 xfail:0 xpass:0 skip:0 error:0

I've not had time yet to dig into what's going on, but let me know if
you need any further details.

thanks
-john