linux-kernel - Re: [PATCH] uio: User IRQ Mode

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Date:	Thu, 3 Jul 2008 14:11:22 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
Cc:	"Uwe Kleine-König" <Uwe.Kleine-Koenig@...i.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"hjk@...utronix.de" <hjk@...utronix.de>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH] uio: User IRQ Mode

On Wed, Jul 2, 2008 at 8:31 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>> Note that the irq is disabled instead of acked.  So this should not be a
>> problem.  The userspace part then is responsible to ack (first) and
>> unmask the irq.
>
> That still doesn't make sense.
>
> If you call disable_irq in the IRQ handler you will deadlock because it
> waits until the IRQ handler has completed.

Right, the uio_userirq_handler() function should use
disable_irq_nosync() instead of disable_irq(). Otherwise we'll end up
waiting forever for IRQ_INPROGRESS to be cleared in synchronize_irq()
in the case of CONFIG_SMP.

Thanks!

/ magnus
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