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

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Message-ID: <aec7e5c30807031955v7f304b03jcf7298dfcf90cfa6@mail.gmail.com>
Date:	Fri, 4 Jul 2008 11:55:08 +0900
From:	"Magnus Damm" <magnus.damm@...il.com>
To:	"Hans J. Koch" <hjk@...utronix.de>
Cc:	"Paul Mundt" <lethal@...ux-sh.org>,
	"Uwe Kleine-K??nig" <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>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH] uio: User IRQ Mode

On Fri, Jul 4, 2008 at 4:55 AM, Hans J. Koch <hjk@...utronix.de> wrote:
> On Thu, Jul 03, 2008 at 10:23:16PM +0900, Paul Mundt wrote:
>> On Thu, Jul 03, 2008 at 02:45:05PM +0200, Hans J. Koch wrote:
>> > On Thu, Jul 03, 2008 at 09:10:19AM +0200, Uwe Kleine-K??nig wrote:
>> > >     Moreover this might prevent some bugs.  (And obviously this
>> > >     function has the potential to have a buggy implementation as
>> > >     the comment by Alan Cox shows.)
>> >
>> > For me, this shows two things:
>> >
>> > - I never ever had to use disable_irq_nosync() in any UIO driver yet,
>> >   otherwise I would have noticed.
>> >
>> > - Magnus turned in a patch that he never tested.
>> >
>> Note that the deadlock in question is in relation to SMP, it's true that
>> the patch was never tested in an SMP environment and only on UP, but it
>> certainly was tested.
>
> Ok, so I take back that accusation ;-)

That's good, thank you. In the future it would be even better if you
didn't accuse to begin with, since that will only heat up the
discussion.

> Nonetheless, the patch changes a UIO core file, and everything in there
> should work in all situations on all architectures unless there is a
> _very_ good reason to do something different. This not only applies to
> SMP issues but also to the limitation to non-shared interrupts.

I will resolve the SMP issue and repost, no problem.

>> The vast majority of driver writers don't have a
>> need to use disable_irq_nosync(), so whether you've had to use it or not
>> is largely irrelevant to the conversation at hand ;-)
>
> Sure ;-) I merely wanted to point out that this is an unusual way to
> handle an interrupt.

Grep shows that there is nothing unusual about it.

damm@rx1 ~/git/linux-2.6 $ find drivers/ | xargs grep -m 1 -e
[[:blank:]]disable_irq\( -e [[:blank:]]disable_irq_nosync\( | wc -l
105

/ magnus
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