Re: User mode drivers: part 1, interrupt handling (patch for 2.6.11)

From: Peter Chubb
Date: Sun Mar 13 2005 - 19:03:22 EST

On Gwe, 2005-03-11 at 03:36, Peter Chubb wrote:
> +static irqreturn_t irq_proc_irq_handler(int irq, void *vidp, struct pt_regs *regs)
> +{
> + struct irq_proc *idp = (struct irq_proc *)vidp;
> +
> + BUG_ON(idp->irq != irq);
> + disable_irq_nosync(irq);
> + atomic_inc(&idp->count);
> + wake_up(&idp->q);
> + return IRQ_HANDLED;

Alan> You just deadlocked the machine in many configurations. You can't use
Alan> disable_irq for this trick you have to tell the kernel how to handle it.

Can you elaborate, please? In particular, why doesn't essentially the
same action (disabling an interrupt before the EOI) in
note_interrupt() not lock up the machine?

I can see there'd be problems if the code allowed shared interrupts,
but it doesn't.

Dr Peter Chubb peterc AT
The technical we do immediately, the political takes *forever*
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