On Tue, Nov 11, 2008 at 06:03:27PM +0100, Oleg Nesterov wrote: > 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. Indeed, some of the things I am doing as part of the hierarchical RCU implementation need to be applied to preemptable RCU. :-/ Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
