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-rw-r--r--arch/x86/kernel/topology.c51
1 files changed, 51 insertions, 0 deletions
diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
index 0e7b4a7a7fb8..6e60b5fe2244 100644
--- a/arch/x86/kernel/topology.c
+++ b/arch/x86/kernel/topology.c
@@ -50,6 +50,57 @@ static int __init enable_cpu0_hotplug(char *str)
__setup("cpu0_hotplug", enable_cpu0_hotplug);
#endif
+#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
+/*
+ * This function offlines a CPU as early as possible and allows userspace to
+ * boot up without the CPU. The CPU can be onlined back by user after boot.
+ *
+ * This is only called for debugging CPU offline/online feature.
+ */
+int __ref _debug_hotplug_cpu(int cpu, int action)
+{
+ struct device *dev = get_cpu_device(cpu);
+ int ret;
+
+ if (!cpu_is_hotpluggable(cpu))
+ return -EINVAL;
+
+ cpu_hotplug_driver_lock();
+
+ switch (action) {
+ case 0:
+ ret = cpu_down(cpu);
+ if (!ret) {
+ pr_info("CPU %u is now offline\n", cpu);
+ kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
+ } else
+ pr_debug("Can't offline CPU%d.\n", cpu);
+ break;
+ case 1:
+ ret = cpu_up(cpu);
+ if (!ret)
+ kobject_uevent(&dev->kobj, KOBJ_ONLINE);
+ else
+ pr_debug("Can't online CPU%d.\n", cpu);
+ break;
+ default:
+ ret = -EINVAL;
+ }
+
+ cpu_hotplug_driver_unlock();
+
+ return ret;
+}
+
+static int __init debug_hotplug_cpu(void)
+{
+ _debug_hotplug_cpu(0, 0);
+ return 0;
+}
+
+late_initcall_sync(debug_hotplug_cpu);
+#endif /* CONFIG_DEBUG_HOTPLUG_CPU0 */
+
int __ref arch_register_cpu(int num)
{
struct cpuinfo_x86 *c = &cpu_data(num);