Re: [Xenomai-core] Spinlock question.

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

[-- Attachment #1: Type: text/plain, Size: 1261 bytes --]

Gilles Chanteperdrix wrote:
> Hi,
> 
> I am porting a network driver from Linux to RTnet, and I have a sudden
> doubt about what I am doing: is it safe to call a function like
> wake_up_interruptible, from a non real-time context, with CONFIG_PREEMPT
> enabled, while holding an rthal spinlock ? Do not I risk a rescheduling
> with the spinlock locked ?

Mmh, doesn't stalling the primary domain (what rthal_spin_lock_irqsave
surely does) also make the root domain think it is running in interrupt
context, thus will prevent any Linux reschedule?

However, there is one big fat issue with this approach:
wake_up_interruptible takes some Linux spin lock. So you must never call
it from primary context on UP to avoid corruption. And an SMP, you
create a nice source for priority inversion: CPU2 holds wait_queue lock,
gets preempted by Xenomai and runs some longer low-prio RT job.
Meanwhile CPU1 tries to acquire wait_queue as well with IRQs disabled,
blocking any RT task on that CPU.

Better defer the Linux wake-up via a rtdm_nrtsig. Alternatively, make
the Linux waiter also a Xenomai task and use a rtdm_event e.g. (mmh,
maybe we should discuss the auto-shadow-any-Linux-task-on-demand feature
for Xenomai once again...).

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]