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    SubjectRe: [PATCH v3 2/4] genirq: Inform handler about line sharing state
    Am 15.12.2010 14:04, Thomas Gleixner wrote:
    > On Wed, 15 Dec 2010, Jan Kiszka wrote:
    >> Am 14.12.2010 21:54, Thomas Gleixner wrote:
    >>> On Mon, 13 Dec 2010, Jan Kiszka wrote:
    >>>> @@ -943,6 +950,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
    >>>> /* Make sure it's not being used on another CPU: */
    >>>> synchronize_irq(irq);
    >>>> + if (single_handler)
    >>>> + desc->irq_data.drv_status &= ~IRQS_SHARED;
    >>>> +
    >>> What's the reason to clear this flag outside of the desc->lock held
    >>> region.
    >> We need to synchronize the irq first before clearing the flag.
    >> The problematic scenario behind this: An IRQ started in shared mode,
    >> this the line was unmasked after the hardirq. Now we clear IRQS_SHARED
    >> before calling into the threaded handler. And that handler may now think
    >> that the line is still masked as IRQS_SHARED is set.
    > That should read "not set" I guess.

    Can't remember who wrote this, but that guy might have been too tired
    for clear sentences: Yes, of course, we could run into troubles, if
    IRQS_SHARED was _not_ set while the IRQ line is unmasked between hard
    and threaded handler.

    > Hmm, needs more thoughts :(

    Be warned, might be painful.


    Siemens AG, Corporate Technology, CT T DE IT 1
    Corporate Competence Center Embedded Linux

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