On Friday, August 09, 2013 04:16:56 PM Toshi Kani wrote: > On Fri, 2013-08-09 at 15:28 +0800, Tang Chen wrote: > > On 08/07/2013 12:56 AM, Toshi Kani wrote: > > > On Tue, 2013-08-06 at 19:11 +0900, Yasuaki Ishimatsu wrote: > > >> try_offline_node() checks that all cpus related with removed node have been > > >> removed by using cpu_present_bits. If all cpus related with removed node have > > >> been removed, try_offline_node() clears the node information. > > >> > > >> But try_offline_node() called from acpi_processor_remove() never clears > > >> the node information. For disabling cpu_present_bits, acpi_unmap_lsapic() > > >> need be called. But acpi_unmap_lsapic() is called after try_offline_node() > > >> runs. So when try_offline_node() runs, the cpu's cpu_present_bits is always > > >> set. > > >> > > >> This patch moves try_offline_node() after acpi_unmap_lsapic(). > > >> > > >> Signed-off-by: Yasuaki Ishimatsu<isimatu.yasuaki@xxxxxxxxxxxxxx> > > > > > > The change looks good to me. > > > > > > Acked-by: Toshi Kani<toshi.kani@xxxxxx> > > > > > > BTW, do you know why try_offline_node() has to use stop_machine()? > > > > try_offline_node() is used to check if the node could be hot-removed > > after each memory or cpu hot-remove operation. > > > > In memory hot-remove path, we have lock_memory_hotplug() to series all > > the memory hot-remove options. > > > > But when doing cpu hot-remove, > > > > acpi_processor_remove() > > |->try_offline_node() > > > > There is no lock to protect it. I think, when we are going to hot-remove > > a node, others should not do any memory or cpu hotplug operation. In memory > > hotplug path, we have lock_memory_hotplug(). But in cpu hotplug path, I > > didn't find any lock. So we used stop_machine() to call check_cpu_on_node(). > > If we find any cpu still present, we return and do not remove the node. > > CPU/Memory hotplug operations and sysfs eject are serialized with > acpi_os_hotplug_execute(). CPU online/offline is protected by > cpu_hotplug_[begin|done]() and [get|put]_online_cpus(). But, yes, > online/offline and hotplug operations are not serialized. I tried to > serialize them before, but that framework was not well received. What about lock_device_hotplug()? It is taken by both online/offline and the ACPI hotplug code, isn't it? > Anyway, it looks to me that cpu_up()->mem_online_node() path can race > with try_offline_node(). It can in principle, but I'm not sure if there's a way to trigger that race. Do you have an example? Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
