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

Thomas Gleixner
2009-03-01T09:44:25Z

On Sat, 28 Feb 2009, David Brownell wrote:
> That seems to presume a hardirq-to-taskirq handoff. But the
> problem case is taskirq-to-taskirq chaining, through e.g.
> what set_irq_chip_and_handler() provided. (Details not very
> amenable to brief emails, just UTSL.)
>
> Thing is, I'm not sure a per-IRQ thread can work easily with
> that chaining. The chained IRQs can need to be handled before
> the top-level IRQ gets re-enabled. That's why the twl4030-irq
> code uses just one taskirq thread for all incoming events.

This can be solved by a completion as well.

> (Which of course is rarely more than one at a time, so there's
> little reason not to share that task between the demuxing code
> and the events being demuxed. Interrupts that need processing
> via I2C/SPI/etc are more or less by definition not frequent or
> performance-critical.)

Then all we need to provide in the generic code is a function which
does not go through the handle_IRQ_event() logic and calls the action
handler directly. Not rocket science to do that and better than using
a facility which is designed to run in hardirq context and expect that
it works in thread context without complaints.

Thanks,

tglx