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    SubjectRe: [PATCH] x86, kdump: No need to disable ioapic in crash path
    On Tue, Feb 07, 2012 at 03:35:59PM -0800, Eric W. Biederman wrote:
    > Vivek Goyal <vgoyal@redhat.com> writes:
    >
    > > On Tue, Feb 07, 2012 at 04:57:41PM -0500, Don Zickus wrote:
    > >> On Thu, Feb 02, 2012 at 03:24:46PM -0800, Eric W. Biederman wrote:
    > >> > > Eric, brought up a point that because the boot code was restructured we may
    > >> > > not need to disable the io apic any more in the crash path. The original
    > >> > > concern that led to the development of disable_IO_APIC, was that the TSC
    > >> > > calibration on boot up relied on the PIT timer for reference. Access
    > >> > > to the PIT required 8259 interrupts to be working. This wouldn't work
    > >> > > if the ioapic needed to be configured. So on panic path, the ioapic was
    > >> > > reconfigured to use virtual wire mode to allow the 8259 to passthrough.
    > >> >
    > >> > A small clarification originally it was the jiffies calibration that
    > >> > would fail if we could cause the PIT to generate interrupts through the
    > >> > 8259. The boot would then hang at calibrating jiffies.
    > >>
    > >> Ok. Thanks!
    > >
    > > So now what has changed? Do we setup LAPIC and IOAPIC early enough to
    > > receive PIT interrupts in regular mode (non-virtual wire mode) or
    > > something else?
    >
    > Yes. Part of the Moorstown work required that this be done because
    > moorsetown did not support legacy mode. Last I looked the code hadn't
    > been generalized beyond Moorsetown but empirically it works now.
    >
    > Don as to what to test the only case I can think of that might be spooky
    > is a screaming interrupt during the handover. You might want to try
    > playing with lkcdtm to try some of the more exotic crash scenarios. But
    > all I expect further testing might reveal are places where we are not
    > as robust in initializing the hardware as we might be. Things that
    > might have been papered over by the ioapic shutdown.

    I ran lkdtm by panic'ing in the interrupt handle thus leaving device
    interrupt un-ack'd and the apic might have been un-ack'd too (jprobes
    hooked in at do_IRQ). 3 out 3 times the second kernel came up on my core2
    quad.

    Cheers,
    Don


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