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

Steven Rostedt
2006-05-12T07:59:48Z

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.
>