Re: [Xenomai] Question about scheduling and signals

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 05/24/2014 09:05 PM, Matthias Schneider wrote:
> Hi all,
> 
> currently I am trying to make the following FreeRTOS test case run on 
> forge/mercury on linux preempt_rt:
> 
> 
> //Task 1, prio 1 / SCHED_FIFO
> for(;;) {
>   (*pulCounter)++;
>   if( *pulCounter >= priMAX_COUNT )
>      vTaskSuspend(NULL); // -> wait for signal SIGRESM
> }
> 
> //Task 2, prio 0 / SCHED_OTHER
> vTaskSuspendAll(); //-> sched_lock
> vTaskResume(xLimitedIncrementHandle); //-> sends SIGRESM
> xTaskResumeAll(); //-> sched_unlock, seems not to unlock the waiting task
>                   // right away (because signal is not yet delivered?)

At this point, task 1 wakes up, increments ulCounter again, then suspend
again, so now ulCounter == priMAX_COUNT + 1

> if (ulCounter != priMAX_COUNT)
>   raise(SIGABRT);

So this test fails, and you get a SIGABORT

I do not see how this test could do anything else than throwing a
SIGABORT. Also note that on multi-processor systems, if task 0 and task
1 are not running on the same CPU, there is a race between task 1
incrementing the counter and task 2 reading its value to compare it to
priMAX_COUNT.



-- 
                                                                Gilles.