Re: lockdep and threaded IRQs (was: ...)

Ingo Molnar
2009-03-03T00:45:15Z

* David Brownell <david-b@pacbell.net> wrote:

> On Monday 02 March 2009, Ingo Molnar wrote:
> > >
> > > The significant omission is lack of support for chaining
> > > such threads.  Example, an I2C device that exposes
> > > several dozen IRQs with mask/ack/... operations that
> > > require I2C access.
> >
> > Well, those are rarely used, embedded-only constructs - the main
> > focus of IRQ threading patches are the more common patterns.
>
> Yes, mostly for embedded, where "system bus" more likely
> means I2C than PCI.
>
>
> > Since you care about them - could you please send patches on top
> > of the IRQ threading patches to add support for them?
>
> I'll look at that, and try to prepare something on top
> of the version of the threading patches that gets into
> the -next tree. I got the impression there was going
> to be a v3 of those patches soonish...

Great! We'll sort out any conflicts so dont worry about that -
you can pick up v2 just fine and post patches.

> I expect there will be two basic parts of that work:
>
> - One to cope with the upcoming change to handle_irq(),
> insisting that it live in hardirq context instead of
> just an irqs-off context (and thereby preventing use
> of standard chaining calls in irq threads, sigh).
>
> - Another to set up a chaining thread, since chain
> setup bypasses setup_irq() and friends.

If you mean to push the chaining bits into the IRQ thread too, i
think the chaining bits actually should never be threaded. Is
there a good reason to do that? It's not like they will really
be preemptible (preempting a chaining thread would mean the
whole demuxing chain is held up => bad).

> That latter might touch what the v2 patches added,
> since I'd want it to share code.

Sure.

>
> - Dave
>
> p.s. Note that those changes would still leave the
> lockdep bug around ... it will still be breaking
> various drivers that use normal IRQs, by forcibly
> enabling IRQF_DISABLED.

it's not a bug - and i think Peter explained that already. It's
not really breaking things either - we've had this for more than
2 years.

Ingo