linux-kernel - Re: [PATCH 05/15] drivers/char: minor irq handler cleanups

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Date:	Tue, 22 Apr 2008 18:05:40 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Rogier Wolff <R.E.Wolff@...Wizard.nl>
Cc:	Jeff Garzik <jeff@...zik.org>, alan@...hat.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/15] drivers/char: minor irq handler cleanups


On Sat, 2008-04-19 at 08:00 +0200, Rogier Wolff wrote:
> 
> You added a "XXX Using free_irq in the interrupt is not wise!". When I
> wrote that code, I didn't know about this. These lines triggered when
> the level-triggered PCI interrupt stuck "active" this would mean that
> NO userspace code would get executed anymore: Hard lock up. Difficult
> to debug. This happend a few times during development when the code
> behind the "if (!polled)": "tell the hardware we've seen the
> interrupt" didn't work. On the other hand, some failures in the field
> have triggered this. So I think it's wise to keep it in. Disabling the
> interrupt on the card is not an option, because that's exactly what
> this is supposed to catch: We're unable to make the card stop
> interrupting the CPU.
> 
> Note that it also doesn't work (i.e. hard lock of the machine) if some
> other driver is using the same interupt.

You should let the kernel generic code deal with the runaway interrupt,
it should be capable of doing so nowadays pretty reliably.

free_irq() is definitely not going to be happy when it start messing
with /proc from an interrupt... It will at least give you a WARN_ON.

Ben.


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