[Xenomai] RTDM !xnpod_unblockable_p() question

Philippe Gerum rpm at xenomai.org
Wed Aug 13 14:52:45 CEST 2014

On 08/13/2014 02:28 PM, Michael Smith wrote:
> Hi
> I have been struggling with this problem for days on end, but there is just
> not enough information in the code
> or documentation for me to solve it.
> I am calling rtdm_mutex_lock() inside a device driver module. It is called
> by my PCI probe function as
> the driver is initializing.
> I keep on getting the error message:
> Xenomai: assertion failed at kernel/xenomai/skins/rtdm/drvlib.c:1534
> (!xnpod_unblockable_p())
> And the resultant -EPERM error message from the return of the function.
> I know these checks were inserted to stop any call from an incorrect
> context. But as far as the documentation states
> it can be called from a kernel module.

The doc (2.6) reads:

 * This service can be called from:
 * - Kernel-based task
 * - User-space task (RT)

The generic "kernel module" context is not mentioned. You get -EPERM
because you cannot call this from a probe() routine, which runs in
secondary/pure linux mode. Acquiring a RTDM mutex requires the caller to
run in real-time mode.

> Also as the mail form March 2006 states
> http://www.xenomai.org/pipermail/xenomai/2006-March/003116.html
> !xnpod_unblockable_p():
> - allows blockable RT-context (kernel and user threads)
> - rejects user threads in secondary mode
> - rejects Linux threads
> Is there something I'm missing with regards to the calling context?
> Are there any other situations this could also produce this return?
> Because as far as I can see it should fine being called in a kernel module.
> Thanks
> Michael Smith
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