From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Wed, 31 Mar 2010 19:43:34 +0200
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-core] syscall restart issue with SIGINFO handlers
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: xenomai-core <xenomai@xenomai.org>

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Hi Gilles,
>>
>> here is a case so far uncaught by Xenomai syscall restart code:
>>
>> #include <pthread.h>
>> #include <stdio.h>
>> #include <signal.h>
>> #include <unistd.h>
>> #include <sys/mman.h>
>> #include <native/task.h>
>> #include <native/mutex.h>
>>
>> RT_MUTEX mutex;
>> pthread_t pthread;
>>
>> void sighand1(int sig)
>> {
>> 	printf("signal 1: %d\n", sig);
>> }
>>
>> void sighand2(int sig, siginfo_t *si, void *context)
>> {
>> 	printf("signal 2: %d\n", sig);
>> }
>>
>> void thread(void *arg)
>> {
>> 	int res1, res2;
>>
>> 	pthread = pthread_self();
>>
>> 	res1 = rt_mutex_acquire(&mutex, TM_INFINITE);
>>
>> 	res2 = rt_mutex_release(&mutex);
>>
>> 	printf("res = %d / %d\n", res1, res2);
>> }
>>
>> int main()
>> {
>> 	struct sigaction sa;
>> 	RT_TASK task_main, task;
>>
>> 	mlockall(MCL_CURRENT|MCL_FUTURE);
>>
>> 	signal(SIGUSR1, sighand1);
>>
>> 	sigemptyset(&sa.sa_mask);
>> 	sa.sa_sigaction = sighand2;
>> 	sa.sa_flags = SA_SIGINFO;
>> 	sigaction(SIGUSR2, &sa, NULL);
>>
>> 	rt_task_shadow(&task_main, "main", 1, 0);
>>
>> 	rt_mutex_create(&mutex, "mutex");
>> 	rt_mutex_acquire(&mutex, TM_INFINITE);
>>
>> 	rt_task_spawn(&task, "thread", 0, 2, 0, thread, 0);
>>
>> 	sleep(1);
>> 	pthread_kill(pthread, SIGUSR1);
>>
>> 	sleep(1);
>> 	pthread_kill(pthread, SIGUSR2);
>>
>> 	rt_mutex_release(&mutex);
>>
>> 	rt_task_delete(&task);
>>
>> 	return 0;
>> }
>>
>>
>> Sending SIGUSR2 will make the blocked thread see -EINTR as result of its
>> rt_mutex acquire. Some different path must be taken by libc when
>> delivering SA_SIGINFO signals and returning to the application. Can you
>> confirm this?
> 
> If you want syscalls to be automatically restarted, you should pass the
> SA_RESTART flag to sigaction. It is unrelated to SA_SIGINFO unless I
> missed something.

Oh, indeed, that works. Should explain the issue in the field, my
colleagues likely missed that too.

Thanks,
Jan

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