[Oneiric] [PATCH 0/1] x86, kdump, ioapic: Reset remote-IRR in clear_IO_APIC

Brad Figg brad.figg at canonical.com
Thu Dec 8 19:24:16 UTC 2011

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

 arch/x86/kernel/apic/io_apic.c |   48 +++++++++++++++++++++++++++++++++++++++-
 1 files changed, 47 insertions(+), 1 deletions(-)


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