From: Vivek Goyal o Kdump broke in 2.6.19-rc4-mm1 on i386 due to LAPIC timer interrupt handling changes. (clock events) o Problems happens because a pending LAPIC timer interrupt is received as soon as kernel enables interrupts first time during boot but associated clock event device has not been initialized yet and kernel crashes. o One can receive a pending LAPIC timer interrupt from previous kernel's context (as in kdump). o A pending LAPIC timer interrupt is delivedred to CPU in second kernel as soon as interrupts are enabled. Already idt vector has been set to handle LAPIC timer interrupts but actually LPAIC is setup in setup_local_APIC() much later. setup_local_APIC() also initializes LAPIC timer and in turn related clock_event_device. But here interrupts comes really early and LAPIC has not been set, associated clock_event_device structure has not been initialized hence kernel crashes in smp_apic_timer_interrupt(). o One of the possible solution is that register the LAPIC timer vector late after LAPIC has been initialized. But this would only solve the problem for boot cpu and not other cpus. o In this patch, I check for clock_event_device event handler and if handler is NULL, that interrupt is ignored as spurious one. Not the best way to handle the situation as it does not count for bugs in clock_event_device creation and registration logic, and also introduces un-necessary check in fastpath. Pleaes suggest if there is a better way to handle this. Signed-off-by: Vivek Goyal Cc: Thomas Gleixner Acked-by: Ingo Molnar Cc: "Eric W. Biederman" Cc: john stultz Signed-off-by: Andrew Morton --- arch/i386/kernel/apic.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff -puN arch/i386/kernel/apic.c~clockevents-core-check-for-clock-event-device-handler-being-non-null-before-calling-it arch/i386/kernel/apic.c --- a/arch/i386/kernel/apic.c~clockevents-core-check-for-clock-event-device-handler-being-non-null-before-calling-it +++ a/arch/i386/kernel/apic.c @@ -546,6 +546,22 @@ static fastcall void local_apic_timer_in return; } + /* Normally we should not be here till LAPIC has been initialized + * but in some cases like kdump, its possible that there is a + * pending LAPIC timer interrupt from previous kernel's context + * and is delivered in new kernel the moment interrupts are enabled. + * + * Interrupts are enabled early and LAPIC is setup much later, hence + * its possible that when we get here evt->event_handler is NULL. + * Check for event_handler being NULL and discard the interrupt + * as spurious. + */ + + if (!evt->event_handler) { + printk("Spurious LAPIC timer interrupt on cpu %d\n", cpu); + return; + } + per_cpu(irq_stat, cpu).apic_timer_irqs++; evt->event_handler(regs); _