linux-kernel - Re: [PATCH] warn about shared irqs requesting IRQF_DISABLED registered with setup

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Message-ID: <20091129151840.GA30813@shareable.org>
Date:	Sun, 29 Nov 2009 15:18:40 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Eric Miao <eric.y.miao@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	John Stultz <johnstul@...ibm.com>,
	Nicolas Pitre <nico@...vell.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] warn about shared irqs requesting IRQF_DISABLED registered with setup_irq

Uwe Kleine-König wrote:
> Hello,
> 
> On Sun, Nov 29, 2009 at 02:31:18AM +0000, Jamie Lokier wrote:
> > Thomas Gleixner wrote:
> > > What about analysing the code and verifying that the setup order is
> > > correct ?
> > > 
> > > Adding save/restore_irq just because you have no clue what the code
> > > does is utter nonsense.
> > 
> > Wouldn't it be quite a lot nicer if generic setup moved the
> > IRQF_DISABLED handler to be first in the list, if that actually works
> > in a useful way rather than simply being a quirk that irqs are
> > disabled for the first one?
> Hmm, what happens if an ISR runs with irqs disabled even though it
> doesn't expect it?  I wouldn't bet that nothing breaks.

Moving the IRQF_DISABLED handler to be first will run an ISR with
interrupts disabled which *does* expect it, so that's good.

According to this thread, at the moment when you have multiple
IRQF_DISABLED|IRQF_SHARED ISRs, only the first one is run with
interrupts disabled.

In fact I don't see why the kernel cannot put _all_ of the
IRQ_DISABLED handlers at the beginning of the list, traverse those
with interrupts disabled, then enable interrupts them for the
remaining handlers.

> IMHO the best is if a warning is printed or registering fails if shared
> irq actions don't agree about wanting IRQF_DISABLED.

On the hardware in question, the debug and timer interrupts share a
line, and I'm guessing only the timer interrupt should have IRQF_DISABLED.

Or we could do away with this silliness and just switch everything to
threaded interrupts with RT-priorities ;-)

-- Jamie
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