What's the source of the "never happen" comment in
arch/i386/kernel/apic.c (repeated in the printk)? It plainly *does*
happen (as Google and my own experience attest--look for
call_spurious_interrupt, though), and there's nothing in Intel's
documentation to suggest that it shouldn't, or that it's anything but
a routine (though presumably rare) occurrence.
(Note also that the documentation reference is no longer correct. In
the 2001 edition it was 7.6.13.5; in the latest edition the APIC gets
its own chapter.)
>8.9. SPURIOUS INTERRUPT
>A special situation may occur when a processor raises its task
>priority to be greater than or equal to the level of the interrupt
>for which the processor INTR signal is currently being asserted. If
>at the time the INTA cycle is issued, the interrupt that was to be
>dispensed has become masked (programmed by software), the local APIC
>will deliver a spurious-interrupt vector. Dispensing the
>spurious-interrupt vector does not affect the ISR, so the handler
>for this vector should return without an EOI.
>/*
> * This interrupt should _never_ happen with our APIC/SMP architecture
> */
>asmlinkage void smp_spurious_interrupt(void)
>{
> unsigned long v;
>
> /*
> * Check if this really is a spurious interrupt and ACK it
> * if it is a vectored one. Just in case...
> * Spurious interrupts should not be ACKed.
> */
> v = apic_read(APIC_ISR + ((SPURIOUS_APIC_VECTOR & ~0x1f) >> 1));
> if (v & (1 << (SPURIOUS_APIC_VECTOR & 0x1f)))
> ack_APIC_irq();
>
> /* see sw-dev-man vol 3, chapter 7.4.13.5 */
> printk(KERN_INFO "spurious APIC interrupt on CPU#%d, should
>never happen
>.\n",
> smp_processor_id());
>}
--
/Jonathan Lundell.