1 files changed, 83 insertions, 1 deletions

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 6dae6a3d2d59..ed1576981801 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -1,14 +1,96 @@
 /*
  * Common SMP CPU bringup/teardown functions
  */
+#include <linux/err.h>
+#include <linux/smp.h>
 #include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/percpu.h>
+#include <linux/workqueue.h>
 
 #include "smpboot.h"
 
+#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
+struct create_idle {
+	struct work_struct	work;
+	struct task_struct	*idle;
+	struct completion	done;
+	unsigned int cpu;
+};
+
+static void __cpuinit do_fork_idle(struct work_struct *work)
+{
+	struct create_idle *c = container_of(work, struct create_idle, work);
+
+	c->idle = fork_idle(c->cpu);
+	complete(&c->done);
+}
+
+static struct task_struct * __cpuinit idle_thread_create(unsigned int cpu)
+{
+	struct create_idle c_idle = {
+		.cpu	= cpu,
+		.done	= COMPLETION_INITIALIZER_ONSTACK(c_idle.done),
+	};
+
+	INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
+	schedule_work(&c_idle.work);
+	wait_for_completion(&c_idle.done);
+	destroy_work_on_stack(&c_idle.work);
+	return c_idle.idle;
+}
+
+/*
+ * For the hotplug case we keep the task structs around and reuse
+ * them.
+ */
+static DEFINE_PER_CPU(struct task_struct *, idle_threads);
+
+static inline struct task_struct *get_idle_for_cpu(unsigned int cpu)
+{
+	struct task_struct *tsk = per_cpu(idle_threads, cpu);
+
+	if (!tsk)
+		return idle_thread_create(cpu);
+	init_idle(tsk, cpu);
+	return tsk;
+}
+
+struct task_struct * __cpuinit idle_thread_get(unsigned int cpu)
+{
+	return per_cpu(idle_threads, cpu);
+}
+
+void __init idle_thread_set_boot_cpu(void)
+{
+	per_cpu(idle_threads, smp_processor_id()) = current;
+}
+
+/**
+ * idle_thread_init - Initialize the idle thread for a cpu
+ * @cpu:	The cpu for which the idle thread should be initialized
+ *
+ * Creates the thread if it does not exist.
+ */
+static int __cpuinit idle_thread_init(unsigned int cpu)
+{
+	struct task_struct *idle = get_idle_for_cpu(cpu);
+
+	if (IS_ERR(idle)) {
+		printk(KERN_ERR "failed fork for CPU %u\n", cpu);
+		return PTR_ERR(idle);
+	}
+	per_cpu(idle_threads, cpu) = idle;
+	return 0;
+}
+#else
+static inline int idle_thread_init(unsigned int cpu) { return 0; }
+#endif
+
 /**
  * smpboot_prepare - generic smpboot preparation
  */
 int __cpuinit smpboot_prepare(unsigned int cpu)
 {
-	return 0;
+	return idle_thread_init(cpu);
 }