Messages in this thread | | | Date | Tue, 11 Nov 2008 18:03:27 +0100 | From | Oleg Nesterov <> | Subject | Q: force_quiescent_state && cpu_online_map |
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I don't think this matters, but still...
force_quiescent_state:
* cpu_online_map is updated by the _cpu_down() * using __stop_machine(). Since we're in irqs disabled * section, __stop_machine() is not exectuting, hence * the cpu_online_map is stable. * * However, a cpu might have been offlined _just_ before * we disabled irqs while entering here. * And rcu subsystem might not yet have handled the CPU_DEAD * notification, leading to the offlined cpu's bit * being set in the rcp->cpumask. * * Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent * sending smp_reschedule() to an offlined CPU. */ cpus_and(cpumask, rcp->cpumask, cpu_online_map); cpu_clear(rdp->cpu, cpumask); for_each_cpu_mask_nr(cpu, cpumask) smp_send_reschedule(cpu);
However,
// called by __stop_machine take_cpu_down() arch/x86/kernel/smpboot.c:cpu_disable_common()
/* * HACK: * Allow any queued timer interrupts to get serviced * This is only a temporary solution until we cleanup * fixup_irqs as we do for IA64. */ local_irq_enable(); mdelay(1); local_irq_disable(); ... remove_cpu_from_maps(cpu);
So it is possible to send the ipi to the dying CPU. I know nothing about this low-level irq code, most probably this is harmless. We already did clear_local_APIC(), but I don't understand what it does.
Oleg.
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