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

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Message-ID: <20080703195538.GC3197@local>
Date:	Thu, 3 Jul 2008 21:55:38 +0200
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	"Hans J. Koch" <hjk@...utronix.de>,
	Uwe Kleine-K??nig <Uwe.Kleine-Koenig@...i.com>,
	Magnus Damm <magnus.damm@...il.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 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 ;-)
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.

> 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.

Thanks,
Hans

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