Re: [Xenomai-core] [Xenomai-git] Jan Kiszka : native: Improve fault tolerance /wrt multiple task deletions

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

Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> GIT version control wrote:
>>> Module: xenomai-jki
>>> Branch: for-upstream
>>> Commit: 5d2fa6c7578683e036d88bc6dbb6a7f458dfe705
>>> URL:    http://git.xenomai.org/?p=xenomai-jki.git;a=commit;h=5d2fa6c7578683e036d88bc6dbb6a7f458dfe705
>>>
>>> Author: Jan Kiszka <jan.kiszka@domain.hid>
>>> Date:   Wed Apr 28 15:08:11 2010 +0200
>>>
>>> native: Improve fault tolerance /wrt multiple task deletions
>>>
>>> As we may pass the pthread handle of an RT_TASK directly to glibc, we
>>> may trigger a SIGSEGV if the underlying thread was already terminated.
>>> Try to catch this application mistakes by clearing the handle at least
>>> in that task descriptor which successfully ran rt_task_delete or
>>> rt_task_join.
>>>
>>> Signed-off-by: Jan Kiszka <jan.kiszka@domain.hid>
>> Ok. I have tested this patch (though I could not find whether it was
>> discussed on the mailing list). And in fact, it looks to me like it
>> turns an application error into a silently working application.
> 
> Then there is probably something broken: rt_task_delete is supposed to
> return -EIDRM of the passed handle no longer exists. That's at least
> what the doc says. The point of this patch is to turn an application
> crash into a proper error return value (and that not only for
> --enable-debug).

Here is the test I used:
#include <stdio.h>
#include <native/task.h>
#include <sys/mman.h>

void task_main(void* arg)
{
        rt_task_sleep(1000000000);
}

int main(void)
{
     RT_TASK task;

     mlockall(MCL_CURRENT|MCL_FUTURE);
     rt_task_create(&task, "task", 128*1024, 99, T_FPU|T_JOINABLE);
     rt_task_start(&task, task_main, NULL);
     fprintf(stderr, "join: %d\n", rt_task_join(&task));
     fprintf(stderr, "delete: %d\n", rt_task_delete(&task));
}

it prints:
join: 0
delete: 0

This said, I like the segfault, because people probably never check the
return value of rt_task_join/rt_task_delete (which is, I guess, the
reason why phtread_cancel and pthread_join segfault themselves, because
the posix spec allows to return ESRCH in that case).

-- 
					    Gilles.