Re: [RFC][PATCH -rt] irqd starvation on SMP by a single process?

Ingo Molnar
2006-05-12T08:11:32Z

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 12 May 2006, Ingo Molnar wrote:
>
> > ah. This actually uncovered a real bug. We were calling __do_softirq()
> > with interrupts enabled (and being preemptible) - which is certainly
> > bad.
>
> Hmm, I wonder if this is also affecting Mark's problem.
>
> But since I showed that if hardirqs_disabled and running PREEMPT not
> PREEMPT_RT, disable_irq can call schedule. This is done in
> drivers/net/3c59x.c. It has a watchdog timeout calling disable_irq,
> which calls synchronize_irq which might schedule:
>
> void synchronize_irq(unsigned int irq)
> {
> struct irq_desc *desc = irq_desc + irq;
>
> if (irq >= NR_IRQS)
> return;
>
> if (hardirq_preemption && !(desc->status & IRQ_NODELAY))
> wait_event(desc->wait_for_handler,
> !(desc->status & IRQ_INPROGRESS));
> else
> while (desc->status & IRQ_INPROGRESS)
> cpu_relax();
> }
>
> -- Steve
>
> >
> > this was hidden before because the smp_processor_id() debugging code
> > handles tasks bound to a single CPU as per-cpu-safe.
> >
> > could you check the (totally untested) patch below and see if that fixes
> > things for you? I've also added your affinity change.
> >