On Tue, May 22, 2012 at 03:50:38PM +0200, Thomas Gleixner wrote:
> On Sun, 20 May 2012, Yong Zhang wrote:
> > On Sun, May 20, 2012 at 01:27:31PM +0800, Yong Zhang wrote:
> > > --- a/kernel/irq/manage.c
> > > +++ b/kernel/irq/manage.c
> > > @@ -41,6 +41,7 @@ early_param("threadirqs", setup_forced_irqthreads);
> > > void synchronize_irq(unsigned int irq)
> > > {
> > > struct irq_desc *desc = irq_to_desc(irq);
> > > + struct irqaction *action = desc->action;
> >
> > Bad time for dereferencing *action.
>
> You meant dereferencing *desc :)
Ah, yes :)
>
> > /*
> > * We made sure that no hardirq handler is running. Now verify
> > * that no threaded handlers are active.
> > + * But for theaded irq, we don't sync if current happens to be
> > + * the irq thread; otherwise we could deadlock.
> > */
> > + action = desc->action;
>
> And dereferencing action w/o being protected by desc->lock is buggy.
>
> + while (action) {
> > + if (action->thread && action->thread == current)
> > + return;
> > + action = action->next;
> > + }
> > +
>
> Aside of that I really do not like that change. It'll hide real
> deadlocks when disable_irq() is called from the interrupt handler.
>
> Also this will not cure all problems of that MMC driver on RT or with
> forced threaded interrupts.
>
> Assume that tasklet code runs from the softirq thread so it will
> schedule when desc->threads_active > 0. This will trigger a
> "scheduling while atomic" warning.
Yes.
>
> The irq_enable/disable dance in that driver is amazing. I have no time
> at the moment to grok the logic behind this, but it bet this can be
> done way simpler and less horrible.
I'll reconsider this issue and try to find the simpler way.
Thanks,
Yong
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