Re: [Xenomai-help] rtdm_event_timedwait hang-up

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> Philippe Gerum wrote:
> 
>>Jan Kiszka wrote:
>>
>>>Petr Cervenka wrote:
>>>
>>>
>>>>Hello,
>>>>I'm trying to port a  driver of a AD card to RTDM.
>>>>When I use rtdm_event_timedwait in IOCTL handler (called from NRT
>>>>user app), the system will hang-up immediately.
>>>>Does it have something to do with:
>>>>https://mail.gna.org/public/xenomai-help/2006-03/msg00035.html
>>>>, ie. it's not possible to call wait /caller blocking functions from
>>>>non-real-time, is it?
>>>
>>>
>>>Yep, that's exactly the point, it's an illegal usage.
>>>
>>>And the fact that this still causes a crash instead of some more
>>>graceful failure reminds me of one reason why I asked for the new
>>>XENO_ASSERT macro: adding debug checks for such mistakes to RTDM.
>>>
>>
>>It would be nice to have all potentially blocking syscalls actively
>>checking for invalid call context, so that we always get graceful
>>returns. At least, I'm in the process of adding the missing checks to
>>the traditional RTOS skins which I'm extending with a native syscall
>>interface. The good news is that it's basically a matter of grepping
>>xnsynch_sleep_on() in the codebase.
>>
>>--- skins/rtdm/drvlib.c    (revision 765)
>>+++ skins/rtdm/drvlib.c    (working copy)
>>@@ -648,6 +648,11 @@
>>     else if (!__test_and_clear_bit(0, &event->pending)) {
>>         xnthread_t  *thread = xnpod_current_thread();
>>
>>+    if (xnpod_unblockable_p()) {
>>+        err = -EPERM;
>>+        goto unlock_and_exit;
>>+    }
>>+
>>         xnsynch_sleep_on(&event->synch_base, XN_INFINITE);
>>
>>         if (!xnthread_test_flags(thread, XNRMID|XNBREAK))
>>@@ -658,6 +663,7 @@
>>             err = -EINTR;
>>     }
>>
>>+ unlock_and_exit:
>>     xnlock_put_irqrestore(&nklock, s);
>>
>>     return err;
> 
> 
> Agree, but I prefer to be able to switch those checks off when the used
> drivers have been verified for correctness.
> 
> Actually, this check is up to them: when some service is invoked from
> the "wrong" context, the driver can return -ENOSYS to let Xenomai switch
> to the right one. It can also return some other error to the user
> instead. Or it can block certain contexts by not registering related
> service handlers.

I agree; there are some RTDM specific issues, especially the adaptive calls.

> 
> As the user never invokes RTDM services directly, I see no need for
> permanent checks. The Linux kernel does such checking also on demand,
> not by default.
>

Yes, but the kernel usually don't go south when a user-level app does a 
mistake. We currently do.

> Jan
> 


-- 

Philippe.