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    Subject[KDUMP] pending interrupts problem
    Hi all,

    I'm having a problem in kdump on a Pentium 4 box when using SMP
    kernel as the second (dump capturing) kernel. Although the use
    of SMP kernel as the second kernel is discouraged in
    Documentation/kdump/kdump.txt, I hope discussing the problem
    here will benefit users in the future.

    I tracked down the problem to write a small module (attached)
    that can reproduce the problem.

    How to reproduce:

    - Configure both the first and the second kernels to be
    - Boot the first kernel with "maxcpus=1"
    - Run "insmod pending-IPI.ko" to oops the second kernel

    The module makes IPI (Inter-Processor Interrupt) pending upon a
    crash. This is done by:

    - Disable local interrupts.
    - Send IPI to CPU#0.
    - Call panic().

    What happens in the second kernel is that it receives the
    pending IPI at the first local_irq_enable() in init/main.c, and
    the IPI handler calls the uninitialized function pointer
    call_data->func in arch/i386/kernel/smp.c.

    One way to solve this problem is to implement some blocking
    mechanism in the IPI handler so that it prevents itself from
    calling the uninitialized pointer.

    But pending interrupts on other vectors may cause another
    problem. They would cause misrouted IRQs, which are now
    addressed by "irqpoll" kernel parameter. But I'm not sure this
    solves all the problems.

    So another way to solve this problem is to clear all such
    pending interrupts before booting the second kernel. This is
    more challenging because the pending status (IRR bits ON) in a
    local APIC can only be cleared by the acceptance of the
    interrupt by CPU core (See section 8.8.4 in "IA-32 Intel(R)
    Architecture Software Developer's Manual Vol.3"). That is, we
    need to enable the interrupt somewhere in a crashed kernel to
    clear the pending status.

    Any other ideas to deal with pending interrupts?


    OBATA Noboru (

    /* pending-IPI.c - Panic a kernel with IPI pending */

    #include <linux/config.h>
    #include <linux/module.h>
    #include <linux/smp.h>

    int init_module(void)

    apic_write_around(APIC_ICR2, SET_APIC_DEST_FIELD(1));
    apic_write_around(APIC_ICR, (APIC_DM_FIXED
    | APIC_DEST_LOGICAL | 0xfb));

    panic("pending-IPI: Bye-bye.");

    return 0;

    MODULE_AUTHOR("OBATA Noboru <>");
    MODULE_DESCRIPTION("Panic a kernel with IPI pending");
     \ /
      Last update: 2005-10-27 09:54    [W:0.044 / U:11.984 seconds]
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