linux-kernel - Re: [PATCH v6 2/2] selftests/timers/posix_timers: Test delivery of signals across threads

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Date: Sat, 6 Apr 2024 23:13:13 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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
Subject: Re: [PATCH v6 2/2] selftests/timers/posix_timers: Test delivery of
 signals across threads

Muhammad,

I am sorry, but... are you aware that this patch was applied over a year ago,
and then this code was updated to use the ksft_API?

Oleg.

On 04/07, Muhammad Usama Anjum wrote:
>
> On 3/16/23 5:30 PM, Marco Elver wrote:
> > From: Dmitry Vyukov <dvyukov@...gle.com>
> > 
> > Test that POSIX timers using CLOCK_PROCESS_CPUTIME_ID eventually deliver
> > a signal to all running threads.  This effectively tests that the kernel
> > doesn't prefer any one thread (or subset of threads) for signal delivery.
> > 
> > Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
> > Signed-off-by: Marco Elver <elver@...gle.com>
> > ---
> > v6:
> > - Update wording on what the test aims to test.
> > - Fix formatting per checkpatch.pl.
> > ---
> >  tools/testing/selftests/timers/posix_timers.c | 77 +++++++++++++++++++
> >  1 file changed, 77 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c
> > index 0ba500056e63..8a17c0e8d82b 100644
> > --- a/tools/testing/selftests/timers/posix_timers.c
> > +++ b/tools/testing/selftests/timers/posix_timers.c
> > @@ -188,6 +188,80 @@ static int check_timer_create(int which)
> >  	return 0;
> >  }
> >  
> > +int remain;
> > +__thread int got_signal;
> > +
> > +static void *distribution_thread(void *arg)
> > +{
> > +	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
> > +	return NULL;
> > +}
> > +
> > +static void distribution_handler(int nr)
> > +{
> > +	if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))
> > +		__atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
> > +}
> > +
> > +/*
> > + * Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
> > + * timer signals. This primarily tests that the kernel does not favour any one.
> > + */
> > +static int check_timer_distribution(void)
> > +{
> > +	int err, i;
> > +	timer_t id;
> > +	const int nthreads = 10;
> > +	pthread_t threads[nthreads];
> > +	struct itimerspec val = {
> > +		.it_value.tv_sec = 0,
> > +		.it_value.tv_nsec = 1000 * 1000,
> > +		.it_interval.tv_sec = 0,
> > +		.it_interval.tv_nsec = 1000 * 1000,
> > +	};
> > +
> > +	printf("Check timer_create() per process signal distribution... ");
> Use APIs from kselftest.h. Use ksft_print_msg() here.
> 
> > +	fflush(stdout);
> > +
> > +	remain = nthreads + 1;  /* worker threads + this thread */
> > +	signal(SIGALRM, distribution_handler);
> > +	err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
> > +	if (err < 0) {
> > +		perror("Can't create timer\n");
> ksft_perror() here
> 
> > +		return -1;
> > +	}
> > +	err = timer_settime(id, 0, &val, NULL);
> > +	if (err < 0) {
> > +		perror("Can't set timer\n");
> > +		return -1;
> > +	}
> > +
> > +	for (i = 0; i < nthreads; i++) {
> > +		if (pthread_create(&threads[i], NULL, distribution_thread, NULL)) {
> > +			perror("Can't create thread\n");
> > +			return -1;
> > +		}
> > +	}
> > +
> > +	/* Wait for all threads to receive the signal. */
> > +	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
> > +
> > +	for (i = 0; i < nthreads; i++) {
> > +		if (pthread_join(threads[i], NULL)) {
> > +			perror("Can't join thread\n");
> > +			return -1;
> > +		}
> > +	}
> > +
> > +	if (timer_delete(id)) {
> > +		perror("Can't delete timer\n");
> > +		return -1;
> > +	}
> > +
> > +	printf("[OK]\n");
> ksft_test_result or _pass variant as needed?
> 
> > +	return 0;
> > +}
> > +
> >  int main(int argc, char **argv)
> >  {
> >  	printf("Testing posix timers. False negative may happen on CPU execution \n");
> > @@ -217,5 +291,8 @@ int main(int argc, char **argv)
> >  	if (check_timer_create(CLOCK_PROCESS_CPUTIME_ID) < 0)
> >  		return ksft_exit_fail();
> >  
> > +	if (check_timer_distribution() < 0)
> > +		return ksft_exit_fail();
> > +
> >  	return ksft_exit_pass();
> >  }
> 
> -- 
> BR,
> Muhammad Usama Anjum
>