Re: PATCH/RFC: [kdump] fix APIC shutdown sequence

Eric W. Biederman wrote:

Ok. Later in the thread it sounds like you have retried this and
irqpoll is working now.

Yes. I'd give a lot to know what went wrong when I tried that in April.
It'd have saved me many hours of work if I had discovered this workaround
before.

Have you done any looking at moving where the kernel initalizes
io_apics? One of the todo items on the path is to leave
io_apic mode enabled and just startup the kernel in io_apic
mode.
I have tried to recover from the "IRR set" situation in several ways by
changing setup_IO_APIC_irq(). But I haven't found a way to recover from
this situation once disable_IO_APIC() had been called.

Yes. The long term goal is to remove the need for calling
disable_IO_APIC(). Because that makes the code simpler etc.

I think a lot would be gained if disable_IO_APIC() would just mask the IRQs
(like the function in my patch does), and perhaps fix the dest ID, instead of
totally clearing the registers.

Moreover, it'd be reasonable to separate out the code that restores virtual
wire mode from disable_IO_APIC().

It is quite possible. I have observed a lot of obscure bugs in the
corner cases of the state machines, although it is possible
this is correct behavior and it is just specific to level
triggered interrupts which are almost exclusively not on
the first ioapic in a system like you describe.

Even if my patch in the form in which I submitted it is unusable,
I think the basic idea that IRQs should be masked bottom-up
(IO-APIC first, then local APIC, then CPU) is correct.

Or is there any specific reason why the current code does it vice-versa?

Martin


--
Martin Wilck
PRIMERGY System Software Engineer
FSC IP ESP DE6

Fujitsu Siemens Computers GmbH
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