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

[Ingo Molnar <mingo@elte.hu>]

* 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.
> >