This patch removes the use of stop_machine() in try_offline_node() and
adds comments to try_offline_node() and remove_memory() that
lock_device_hotplug() is required.
This patch need more verbose explanation. check_cpu_on_node() traverse cpus
and cpu hotplug seems to use cpu_hotplug_driver_lock() instead of
lock_device_hotplug().
As described:
| lock_device_hotplug() serializes hotplug & online/offline operations.
| The lock is held in common sysfs online/offline interfaces and ACPI
| hotplug code paths.
And here are their code paths.
- CPU & Mem online/offline via sysfs online
store_online()->lock_device_hotplug()
- Mem online via sysfs state:
store_mem_state()->lock_device_hotplug()
- ACPI CPU & Mem hot-add:
acpi_scan_bus_device_check()->lock_device_hotplug()
- ACPI CPU & Mem hot-delete:
acpi_scan_hot_remove()->lock_device_hotplug()
O.K.
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