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    SubjectRe: 2.6.19-rc5: known regressions :SMP kernel can not generate ISA irq
    Date
    Ingo Molnar <mingo@redhat.com> writes:

    > On Mon, 2006-11-13 at 10:11 -0700, Eric W. Biederman wrote:
    >> > So when you "mask" an edge-triggered IRQ, you can't really mask it
    >> at all,
    >> > because if you did that, you'd lose it forever if the IRQ comes in
    >> while
    >> > you masked it. Instead, we're supposed to leave it active, and set a
    >> flag,
    >> > and IF the IRQ comes in, we just remember it, and mask it at that
    >> point
    >> > instead, and then on unmasking, we have to replay it by sending a
    >> > self-IPI.
    >> >
    >> > Maybe that part got broken by some of the IRQ changes by Eric.
    >>
    >> Hmm. The other possibility is that this is a genirq migration issue.
    >>
    >> Yep. That looks like it. In the genirq migration the edge and
    >> level triggered cases got merged and previously disable_edge_ioapic
    >> was a noop. Ouch.
    >
    > hm, that should be solved by the generic edge-triggered flow handler as
    > well: we never mask an IRQ first time around, we only mask it if
    > we /already/ have the 'soft' IRQ_PENDING flag set. (in that case the
    > lost edge is not an issue because we have the information already - and
    > the masking will prevent a screaming edge source)
    >
    > but maybe this concept has not been pushed through to the disable/enable
    > irq logic itself? (it's only present in the flow handler) Thomas, do you
    > concur?

    I just looked. I think the logic is actually in there as well.
    I keep forgetting disable != mask.

    I looks like what is really missing is that we aren't setting
    IRQ_DELAYED_DISABLE.

    So I think what we really need to do is just set IRQ_DELAYED_DISABLE.
    Does the patch below look right?


    Eric


    diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
    index 41bfc49..14654e6 100644
    --- a/arch/x86_64/kernel/io_apic.c
    +++ b/arch/x86_64/kernel/io_apic.c
    @@ -790,9 +790,11 @@ static void ioapic_register_intr(int irq
    trigger == IOAPIC_LEVEL)
    set_irq_chip_and_handler_name(irq, &ioapic_chip,
    handle_fasteoi_irq, "fasteoi");
    - else
    + else {
    + irq_desc[irq].status |= IRQ_DELAYED_DISABLE;
    set_irq_chip_and_handler_name(irq, &ioapic_chip,
    handle_edge_irq, "edge");
    + }
    }

    static void __init setup_IO_APIC_irqs(void)
    -
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      Last update: 2006-11-13 22:15    [W:0.024 / U:2.124 seconds]
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