Messages in this thread | | | Date | Fri, 11 Jul 2008 15:15:02 +0900 | From | "Magnus Damm" <> | Subject | Re: [PATCH] uio: uio_pdrv_genirq V2 |
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On Thu, Jul 10, 2008 at 7:30 PM, Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com> wrote: > Alan Cox wrote: >> >> > > + else if (!irq_on && !priv->irq_disabled) >> > > + disable_irq(dev_info->irq); >> > I'm not sure if this is a problem on SMP. Should you use >> > disable_irq_nosync here, too? Probably it's OK. >> >> That one will also deadlock. > Can you explain why? I think irqcontrol is only called in task context. > I only see one possible deadlock and that's disable_irq being called > while the irq is IRQ_INPROGRESS on the same cpu. I'm always willing to > learn. > >> The easiest fix is probably to use test_and_set and friends for each I/O >> operation. > Actually using spinlock + irq_disabled variable is new in V2 of this > patch. Don't know why this changed, though.
Sorry for not being more clear about it. Basically, I wanted to serialize user space access somehow, but I managed to screw it up. =)
Atomic enable-and-disable operations without serialization has this problem:
irq line state task0 task1
enabled enabled write "0" if (!test_and_set_bit()) enabled disabled write "1" if (test_and_clear_bit()) enable_irq() <- ERR disable_irq()
ERR will make the interrupt depth counter underflow.
The best solution in my mind is atomic operations, disable_irq_nosync() in irq handler only, and serialize user space only - not the irq handler.
Or maybe the UIO core layer should serialization in the case of multiple tasks?
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