[Xenomai-core] Re: [PATCH, RFC] nucleus:shared irq and possible ipipe problem

[Dmitry Adamushko <dmitry.adamushko@domain.hid>]

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On 31/12/05, Philippe Gerum <rpm@xenomai.org> wrote:
> ...

> 2) xnintr_irq_handler() gets a cookie which is == xnshared_irq_t* (see
> > xnintr_attach) that may already be invalid at that time or, and that's a
> > problem, become invalid during the execution of xnintr_irq_handler().
> > To prevent that, we could add a flag like IRQ_INPROGRESS but
> >
> > either we have to set/remove it on the adeos layer before the control is
> > passed to the xnintr_irq_handler() (to be sure that cookie is not
> > xnfree()'d. xnintr_detach() will do busy waiting)
> >
>
> Synchronizing the pending IRQs in ipipe_virtualize_irq() should be done
> by polling the proper irq_pending count (and _not_ the hi/lo bits which
> get cleared before the handler is run).


But irq_pending counter (pending_hits in the recent adeos patch) gets
cleared before running the isr handler too.

In ipipe_sync_stage() :
...
            if (--cpudata->irq_pending_hits[irq] == 0) {
                 __clear_bit(rank,
                         &cpudata->irq_pending_lo[level]);
                 ipipe_mark_irq_delivery(ipd,irq,cpuid);
            }
(*)

// run the corresponding isr handler

This code drops the irq_pending_hits to 0 before running the handler.

Doesn't it make the following code wrong ?

for (_cpuid = 0; _cpuid < nr_cpus; _cpuid++)
>         while (ipd->cpudata[_cpuid].irq_pending_hits[irq] > 0)
>                 cpu_relax();


as the handler still can be running / or even about to be run when
ipd->cpudata[_cpuid].irq_pending_hits[irq] is already 0.

We can remove the (*) code at the end of ipipe_sync_stage() so that
irq_pending_hits[irq] may become 0 only after the corresponding isr handler
has completed.

At the same time, the irq_pending counter can't be increased anymore since
we clear the IPIPE_HANDLE_FLAG before doing the busy waiting in
ipipe_unregister_domain() or ipipe_virtualize_irq().


--
>
> Philippe.
>

--
Best regards,
Dmitry Adamushko

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