linux-kernel - Re: Threaded interrupt handlers broken?

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Message-Id: <200908161951.13988.mb@bu3sch.de>
Date:	Sun, 16 Aug 2009 19:51:13 +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 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

> > > So you wake when the thread counter is != 0 after the decrement.
> > > 
> > >  #define atomic_dec_and_test(v) (atomic_sub_return(1, (v)) == 0)
> > 
> > Yeah, isn't that what we want to do? I read the test as "wake other threads,
> > if there are other threads" or something like that.
> 
> No, it's for synchronize_irq(). When there are threaded handlers in
> progress, then sychronize_irq() waits on the waitqueue until they are
> finished. So we wake the queue when the last threaded handler of this
> irq line returns from thread_fn.

Ok, I understand.

-- 
Greetings, Michael.
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