Re: [Xenomai-help] deadlock for rtdm_mutex

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

Huan Fang wrote:
> Hi,
> 
> Sometimes I got below assertion failed:
> 
> xenomai/skins/rtdm/drvlib.c:1544 (mutex_owner != curr_thread)
> 
> Looking into the code,
> /* Redefinition to clarify XENO_ASSERT output */
> 		#define mutex_owner xnsynch_owner(&mutex->synch_base)
> 		XENO_ASSERT(RTDM, mutex_owner != curr_thread,
> 			    err = -EDEADLK; goto unlock_out;);
> 
> Does it mean if the current owner of mutex is different from the requesting thread, then a -EDEADLK error is returned?(which is not documented in RTDM api doc)

If the mutex is contended, the owner _must_ be different from the
current thread.

> In my case, if one thread tries to lock same mutex twice, the assertion is thrown out as well. Could you please explain a bit how does Xenomai detect deadlock?

Quite simple: RTDM mutexes do not support recursion, so you must not
acquire them twice in the same thread. That's a reasonable
simplification of the design you find in the mainline kernel as well e.g.

Jan

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