Re: [PATCH] warn about shared irqs requesting IRQF_DISABLED registered with setup_irq

[Jamie Lokier <jamie@shareable.org>]

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