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


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