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    SubjectRe: [RFC] genirq: Flush the irq thread on synchronization
    On Fri, 2 Dec 2011, Ido Yariv wrote:

    > The current implementation does not always flush the threaded handler
    > when disabling the irq. In case the irq handler was called, but the
    > threaded handler hasn't started running yet, the interrupt will be
    > flagged as pending, and the handler will not run. This implementation
    > has some issues:
    >
    > First, if the interrupt is a wake source and flagged as pending, the
    > system will not be able to suspend.
    >
    > Second, when quickly disabling and re-enabling the irq, the threaded
    > handler might continue to run after the irq is re-enabled without the
    > irq handler being called first. This might be an unexpected behavior.

    I'd wish people would stop calling disable/enable_irq() in loops and
    circles for no reason.

    > In addition, it might be counter-intuitive that the threaded handler
    > will not be called even though the irq handler was called and returned
    > IRQ_WAKE_THREAD.
    >
    > Fix this by always waiting for the threaded handler to complete in
    > synchronize_irq().

    I can see your problem, but this might lead to threads_active leaks
    under certain conditions. desc->threads_active was only meant to deal
    with shared interrupts.

    We explicitely allow a design where the primary handler can leave the
    device interrupt enabled and allow further interrupts to occur while
    the handler is running. We only have a single bit to note that the
    thread should run, but your wakeup would up the threads_active count
    in that scenario several times w/o a counterpart which decrements it.

    The solution for this is to keep the current threads_active semantics
    and make the wait function different. Instead of waiting for
    threads_active to become 0 it should wait for threads_active == 0 and
    the IRQTF_RUNTHREAD for all actions to be cleared. To avoid looping
    over the actions, we can take a similar approach as we take with the
    desc->threads_oneshot bitfield.

    Thanks,

    tglx




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