Re: PCI: MSI interrupts masked using prohibited method

From: Thomas Gleixner
Date: Thu Jul 17 2008 - 13:04:50 EST

On Thu, 17 Jul 2008, Matthew Wilcox wrote:

> On Thu, Jul 17, 2008 at 05:58:26PM +0200, Thomas Gleixner wrote:
> > > This is a good thought, let's follow it through. What if we simply make
> > > ->mask a no-op for devices which don't support mask bits?
> >
> > Yep. You can also use fasteoi_handler, which just calls ->eoi() after
> > the handler.
> I think that exposes us to a race.
> CPU takes the first interrupt, calls handle_fasteoi_irq(). That
> calls handle_IRQ_event() which calls the device's interrupt handler.
> Interrupt handler reads status register to determine what to do next.
> Device generates second interrupt and changes status register. Second
> interrupt is never delivered because the ->eoi hasn't been called yet.

Yeah, I know. The question is how the hardware works; there is fasteoi
capable hardware around (not on x86) which works with edge type

> I plan to keep using the edge handler which solves this race by
> calling mask_ack(). For MSIs without mask bits, it will do nothing.

Ah, there are ones w/o a mask bit. That detail slipped through.


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