Re: [Xenomai-help] Strange segmentation fault

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

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Ignacio García Pérez wrote:
> Hi,
> 
> I'm experiencing an strange segmentation fault problem. I've boiled down
> the code to the simplest possible program that causes the segfault:
> 
> 1- Set the timer in oneshot mode.
> 2- Create a task.
> 3- Start the task.
> 
> At the task function:
> 
> 1- Make the task periodic (1s).
> 2- Issue a fprintf.
> 
> That's all. The code segfaults. If I remove the fprintf, it won't
> segfault. If I change it for a printf, it won't segfault.
> 
> If I use fprintf but print just "TICK" instead of "TICK %u", it won't
> segfault while the task is running, but it will when the program is
> interrupted (not shown here, but I tried this with a signal handler in
> place that properly deleted the task, though I think this is not
> absolutely necessary).
> 
> I'm totally confused.
> 
> I know I can use fprintf as long as I assume that the RT task will go
> into "secondary" mode at this point because it'll be using linux
> services, and that it will go back to "primary" RT mode on the next call
> to rt_task_wait_period.
> 
> Also, I know that it would be best to use periodic instead of oneshot
> mode, but my program is obviously more complex than this boiled down
> example and really needs oneshot mode.
> 
> Any ideas about what could be the problem?
> 
> Thanks.
> 
> P.S: This is the same problem I described earlier inthe list as caused
> by inb. I though that inb was the cause because removing it avoided the
> segfault, however, it turns out that removing the inb was causing
> another piece of code containing the fprintf not to execute.
> 
> //===========================================================================
> 
> 
> #include <sys/types.h>
> #include <sys/mman.h>
> #include <sys/io.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> 
> #include <native/task.h>
> 
> #include "main.h"
> 
> 
> 
> static RT_TASK    _io_task;
> 
> static void _io_proc (void *arg) {
> 
>    u_long overrun;
> 
>    rt_task_set_periodic(&_io_task, TM_NOW,
> rt_timer_ns2ticks(1000000000LL));
> 
>    for (;;) {
> 
>        rt_task_wait_period(&overrun);
> 
>        fprintf(stderr, "TICK %u\n", 1);
>    }
> }
> 
> 
> 
> static void _cleanup (void) {
>    rt_task_delete(&_io_task);
> }
> 
> 
> 
> static int _init (void) {
> 
>    int r;
> 
>    r = rt_timer_set_mode(TM_ONESHOT);
>    if (r < 0) {
>        fprintf(stderr, "ERROR %i initializing RT\n", r);
>        _cleanup(); return r;
>    }
> 
>    r = rt_task_create(&_io_task, "rtcore_io_task", 0x1000, 10, T_FPU);

Try PTHREAD_STACK_MIN instead of 0x1000 - or, better, leave it 0 and let
Xenomai pick a value for you. Unless you need more than the default
stack (PTHREAD_STACK_MIN * 4) or you are *sure* to get a way with
PTHREAD_STACK_MIN, you should avoid touching this value.

>    if (r < 0) {
>        fprintf(stderr, "ERROR %i creating task\n", r);
>        _cleanup(); return r;
>    }
> 
>    r = rt_task_start(&_io_task, &_io_proc, NULL);
>    if (r < 0) {
>        fprintf(stderr, "ERROR %i starting task\n", r);
>        _cleanup(); return r;
>    }
> 
>    return 0;
> }
> 
> 
> 
> int main (int argc, char **argv) {
> 
>    iopl(3);
>    mlockall(MCL_CURRENT | MCL_FUTURE);
> 
>    if ( _init() < 0) return 1;
> 
>    for (;;) sleep(1);
> 
>    _cleanup();
> 
>    return 0;
> }
> 

Jan


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