On Wed, 15 Dec 2010, Jan Kiszka wrote: > Am 15.12.2010 14:04, Thomas Gleixner wrote: > > On Wed, 15 Dec 2010, Jan Kiszka wrote: > >> Am 14.12.2010 21:54, Thomas Gleixner wrote: > >>> On Mon, 13 Dec 2010, Jan Kiszka wrote: > >>>> @@ -943,6 +950,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id) > >>>> /* Make sure it's not being used on another CPU: */ > >>>> synchronize_irq(irq); > >>>> > >>>> + if (single_handler) > >>>> + desc->irq_data.drv_status &= ~IRQS_SHARED; > >>>> + > >>> > >>> What's the reason to clear this flag outside of the desc->lock held > >>> region. > >> > >> We need to synchronize the irq first before clearing the flag. > >> > >> The problematic scenario behind this: An IRQ started in shared mode, > >> this the line was unmasked after the hardirq. Now we clear IRQS_SHARED > >> before calling into the threaded handler. And that handler may now think > >> that the line is still masked as IRQS_SHARED is set. > > > > That should read "not set" I guess. > > Can't remember who wrote this, but that guy might have been too tired > for clear sentences: Yes, of course, we could run into troubles, if > IRQS_SHARED was _not_ set while the IRQ line is unmasked between hard > and threaded handler. > > > Hmm, needs more thoughts :( > > Be warned, might be painful. Talking about headache. Your solution above does not prevent that scenario. CPU 0 CPU 1 synchronize_irq(); hard irq comes in sees shared and unmasks clear IRQS_SHARED thread handler runs and sees !SHARED Same scenario, just moved by a few lines :) Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
