linux-kernel - Re: Threaded interrupt handlers broken?

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Message-Id: <200908162301.21775.mb@bu3sch.de>
Date:	Sun, 16 Aug 2009 23:01:21 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Threaded interrupt handlers broken?

On Sunday 16 August 2009 22:05:59 Thomas Gleixner wrote:
> On Sun, 16 Aug 2009, Michael Buesch wrote:
> > On Sunday 16 August 2009 16:25:13 Thomas Gleixner wrote:
> > > On Sun, 16 Aug 2009, Michael Buesch wrote:
> > > > On Sunday 16 August 2009 15:22:29 Thomas Gleixner wrote:
> > > >
> > > > > > +		if (0&&unlikely(desc->status & IRQ_DISABLED)) {
> > > > > 
> > > > > So the interrupt is marked disabled. How do you setup the handler
> > > > > ?  And what does the primary handler do ? Can you post your driver
> > > > > code please?
> > > > 
> > > > This patch converts the b43 driver to threaded interrupts:
> > > > http://bu3sch.de/patches/wireless-testing/20090816-1535/patches/002-b43-threaded-irq-handler.patch
> > > 
> > > On the first glance this looks not too bad. the unlocked access to the
> > > irq status registers looks a bit scary, but that is not relevant for
> > > the problem at hand.
> > 
> > Yeah it does ;)
> > 
> > > > It kind of works with this hack applied to kernel/irq/manage.c
> > > 
> > > Hmm. Is the interrupt of the device shared ?
> > 
> > It's registered as shared, but on my machine it is not shared with anything else.
> > 
> > > If yes, what's the other 
> > > device on that interrupt line ? what puzzles me is the fact that the
> > > IRQ_DISABLED flag is set. Is there anything unusual in dmesg ?
> > 
> > Here's my current kernel log with the two patches applied:
> > http://bu3sch.de/misc/dmesg
> 
> Hmm. Nothing interesting AFAICT, but it would be really interesting to
> find out why the IRQ_DISABLED flag is set.
> 
> Can you add some debug into disable_irq() e.g. WARN_ON(irq ==
> BC43_IRQ_NR); so we can see what disables that interrupt.

I do not see a warning, if I put this into __disable_irq():
WARN_ON(irq == 52);
/proc/interrupts shows 52 as IRQ number for b43.
And dmesg shows "... irq 52 on host ... mapped to virtual irq 52".
So I guess the test is OK and the flag is added by some other means.
Maybe by some weird powerpc architecture code?

It seems a little bit weird, however, that the WARN_ON does not even trigger
on module unload, which as far as I can tell should disable the IRQ line
in the free_irq() call (no other shared devices on this IRQ).

-- 
Greetings, Michael.
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