Re: [Xenomai-help] Sporadic PC freeze after rt_task_start

[Jan Kiszka <jan.kiszka@domain.hid>]

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M. Koehrer wrote:
> Hi everybody,
> 
> I noticed a sporadic freeze of my PC using Xenomai 2.3.1 and kernel 2.6.20.4 on a Pentium D.
> adeos-ipipe-2.6.20-i386-1.8-01.patch.
> 
> The freeze happened sporadically on one of our systems, occasionally it took up to 6 hours  to get it.
> Using a PCI Post Code board and writing POST codes to it, I was able to locate the code that was causing
> the issue. And finally I was able to extract it to a very simple program that shows the same behaviour!!
> 
> Here is my simple test program:
> **************************************** BEGIN *****************
> #include <stdio.h>
> #include <sys/mman.h>
> 
> #include <native/task.h>
> #include <native/sem.h>
> 
> 
> RT_TASK taska_desc;
> 
> void mytaska(void *cookie)
> {
>     int i;
> 
>     for (i=0; i < 5; i++)
>     {
>         rt_task_sleep(5000000);
>     }
> }
> 
> int main(void)
> {
>     int i;
>     int j;
>     mlockall(MCL_CURRENT|MCL_FUTURE);
> 
>     for (j=0; j < 100; j++)
>         for (i=10; i < 15000; i++)
>         {
>             rt_task_create(&taska_desc, "mytaska", 0, 81, T_JOINABLE | T_FPU | T_CPU(1));
>             rt_task_start(&taska_desc, &mytaska, NULL);
>             usleep(1500);
> 
>             rt_task_join(&taska_desc);
>             if ( i % 100 == 0)
>                 printf("Loop %i\n", i);
>         }
> 
>     return 0;
> }
> *************************************** END ***********************************
> It is important to know, that I started the kernel with isolcpus=1, i.e. all non-realtime tasks
> are running on CPU 0.
> Somehow it seems to have to do with the usleep() that is following the rt_task_start.
> usleep() is executed on CPU 0 and rt_task_start starts a task on CPU 1...
> Can this be as the begin of usleep() is executed before the task is started but the end of
> usleep() is when the task has already started. Could this be a cause for a race condition?
> 
> I leave the program running for a while and somehow it freezes the PC (only reset works).
> 
> Any feedback on this is welcome!

Maybe you are seeing the same bug like this test exposes:

#include <native/task.h>
#include <sched.h>
#include <sys/mman.h>

void func(void *arg)
{
	rt_task_set_periodic(NULL, TM_NOW, 1000000000LL);
	while(1) rt_task_wait_period(NULL);
}

main()
{
	RT_TASK task;
	cpu_set_t set;

	mlockall(MCL_CURRENT|MCL_FUTURE);
	printf("rt_task_spawn=%d\n", rt_task_spawn(&task, "Receiver", 0,
	       10, 0, func, NULL));
	CPU_ZERO(&set);
	CPU_SET(1, &set);
	printf("sched_setaffinity=%d\n", sched_setaffinity(0,
	       sizeof(cpu_set_t), &set));
	sleep(1);
	printf("rt_task_delete=%d\n", rt_task_delete(&task));
}

Though, this test doesn't hard-lock, just stalls the process in some
zombie state.

This bug is already scheduled for closer examination, stay tuned.

In the meantime: Is it possible to check if
 a) my demo code happens to lock up hard for you?
 b) any behaviour changes with latest xeno-2.3.2/ipipe-1.8-05 and your
    test case?

Thanks for reporting,
Jan


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