+ * In theory there is a race:
+ *
+ * set_ioapic(new_vector) <-- Interrupt is raised before update
+ * is effective, i.e. it's raised on
+ * the old vector.
+ *
+ * So if the target cpu cannot handle that interrupt before
+ * the old vector is cleaned up, we get a spurious interrupt
+ * and in the worst case the ioapic irq line becomes stale.
+ *
+ * But in case of cpu hotplug this should be a non issue
+ * because if the affinity update happens right before all
+ * cpus rendevouz in stop machine, there is no way that the
+ * interrupt can be blocked on the target cpu because all cpus
+ * loops first with interrupts enabled in stop machine, so the
+ * old vector is not yet cleaned up when the interrupt fires.
+ *
+ * So the only way to run into this issue is if the delivery
+ * of the interrupt on the apic/system bus would be delayed
+ * beyond the point where the target cpu disables interrupts
+ * in stop machine. I doubt that it can happen, but at least
+ * there is a theroretical chance. Virtualization might be
+ * able to expose this, but AFAICT the IOAPIC emulation is not
+ * as stupid as the real hardware.
+ *
+ * Anyway, there is nothing we can do about that at this point
+ * w/o refactoring the whole fixup_irq() business completely.
+ * We print at least the irq number and the old vector number,
+ * so we have the necessary information when a problem in that
+ * area arises.