[Xenomai-help] Understanding rtdm_lock_get

[Xenomai-help] Understanding rtdm_lock_get

[Laurent.POYART]

Hi, 

Looking at the xenomai documentation, I saw that the rtdm_lock_get function
can be used in an interrupt service routine. 
This function seems to be base on spinlocks but in my mind, spinlock under
linux on the single CPU doesn't do anything (am I right?). Then I don't
really understand, how the lock mechanism works when there is a race
condition between the rtdm_lock_get in ISR and the rtdm_lock_get_irqsave
function used in an ioctl. Would it be possible to explain me briefly what
is doing rtdm_lock_get on the lock parameter in a single CPU context?

Complementary question:
does rtdm_lock_get_irqsave disables all interrupts?

Thanks in advance.
L.Poyart.

Re: [Xenomai-help] Understanding rtdm_lock_get

[Jan Kiszka]

Laurent.POYART@fr.thalesgroup.com wrote:
> Hi, 
> 
> Looking at the xenomai documentation, I saw that the rtdm_lock_get function
> can be used in an interrupt service routine. 
> This function seems to be base on spinlocks but in my mind, spinlock under
> linux on the single CPU doesn't do anything (am I right?). Then I don't
> really understand, how the lock mechanism works when there is a race
> condition between the rtdm_lock_get in ISR and the rtdm_lock_get_irqsave
> function used in an ioctl. Would it be possible to explain me briefly what
> is doing rtdm_lock_get on the lock parameter in a single CPU context?

On UP, rtdm_lock_get/put are void (that's in contrast to Linux where
spin_lock also disables local preemption so that you can call it from
interruptible contexts without risking deadlocks).

> 
> Complementary question:
> does rtdm_lock_get_irqsave disables all interrupts?

Yes, it does (for the local CPU, of course).

Jan

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