APPLIED: x86, kdump, ioapic: Reset remote-IRR in clear_IO_APIC
On 12/08/2011 12:24 PM, Brad Figg wrote:
BugLink: http://bugs.launchpad.net/bugs/901830
In the kdump scenario mentioned below, we can have a case where
the device using level triggered interrupt will not generate any
interrupts in the kdump kernel.
1. IO-APIC sends a level triggered interrupt to the CPU's local APIC.
2. Kernel crashed before the CPU services this interrupt, leaving
the remote-IRR in the IO-APIC set.
3. kdump kernel boot sequence does clear_IO_APIC() as part of IO-APIC
initialization. But this fails to reset remote-IRR bit of the
IO-APIC RTE as the remote-IRR bit is read-only.
4. Device using that level triggered entry can't generate any
more interrupts because of the remote-IRR bit.
In clear_IO_APIC_pin(), check if the remote-IRR bit is set and if
so do an explicit attempt to clear it (by doing EOI write on
modern io-apic's and changing trigger mode to edge/level on
older io-apic's). Also before doing the explicit EOI to the
io-apic, ensure that the trigger mode is indeed set to level.
This will enable the explicit EOI to the io-apic to reset the
remote-IRR bit.
Suresh Siddha (1):
x86, kdump, ioapic: Reset remote-IRR in clear_IO_APIC
APPLIED: x86, kdump, ioapic: Reset remote-IRR in clear_IO_APIC
