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SubjectRe: The i386 and x86_64 genirq patches are wrong!
Date
Andrew Morton <akpm@osdl.org> writes:

> ebiederm@xmission.com (Eric W. Biederman) wrote:
>>
>> Ingo Molnar <mingo@elte.hu> writes:
>>
>> > here too it's hard for me to give an answer without seeing your specific
>> > changes (against whatever base is most convenient to you). MSI certainly
>> > works fine on current -mm. (at least on my box)
>>
>> Ok. Looking closer. I have found a clear functional bug.
>>
>> When CONFIG_PCI_MSI is not set.
>> move_irq expands to move_native_irq.
>>
>> ack_ioapic_vector
>> move_native_irq
>> ack_ioapic_irq
>> move_irq
>> move_native_irq
>>
>> ack_ioapic_quirk_vector
>> move_native_irq
>> ack_ioapic_quirk_irq
>> move_irq
>> move_native_irq
>>
>> So we wind up calling move_native_irq twice when MSI is disabled where
>> before your conversion we only ever called it once. Luckily in
>> the case where we have the double call vector_to_irq is a noop so
>> we only migration the same irq twice.
>>
>
> OK, but this doesn't seem to answer Ingo's request "could you please send
> that fix to me, against whatever base you have it tested on, and i'll merge
> it to genirq/irqchips [and fix up genirq if needed]. Please also include a
> description of the problem. How common is that edge retrigger problem, and
> how come this has never been seen in the past years since we had
> irqbalance?"
>
> The genirq patches are stuck in limboland until issues like this are
> resolved. I'm not planning on sending them to Linus for 2.6.18 so there's
> no huge rush on it, but it would be nice to get all these loose ends tied
> off reasonably promptly, please.

So to wrap thread up cleanly. Before I start another one.

The bug fix is only important for level triggered irqs if you change
their vector. Since we don't change their vector right now we don't
see a problem.

The two outstanding issues I have with the genirq patches are:

- On x86_64 irq migration was removed. The irq balancer there
is in user space, but we still have it, so not being able
to bind irqs to anything but cpu 0 is a regression.

- On i386 the CONFIG_PCI_MSI defined was mishandled and we attempt
to migrate an irq twice. As I mentioned above.

A new patchset follows shortly that addresses the root cause and
removes the difference in behaviour of io_apic.c present
CONFIG_PCI_MSI is defined.

Eric





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