diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
new file mode 100644
index 0000000..c39ed70
--- /dev/null
+++ b/kernel/stop_machine.c
@@ -0,0 +1,212 @@
+#include <linux/stop_machine.h>
+#include <linux/kthread.h>
+#include <linux/sched.h>
+#include <linux/cpu.h>
+#include <linux/err.h>
+#include <linux/syscalls.h>
+#include <asm/atomic.h>
+#include <asm/semaphore.h>
+#include <asm/uaccess.h>
+
+/* Since we effect priority and affinity (both of which are visible
+ * to, and settable by outside processes) we do indirection via a
+ * kthread. */
+
+/* Thread to stop each CPU in user context. */
+enum stopmachine_state {
+	STOPMACHINE_WAIT,
+	STOPMACHINE_PREPARE,
+	STOPMACHINE_DISABLE_IRQ,
+	STOPMACHINE_EXIT,
+};
+
+static enum stopmachine_state stopmachine_state;
+static unsigned int stopmachine_num_threads;
+static atomic_t stopmachine_thread_ack;
+static DECLARE_MUTEX(stopmachine_mutex);
+
+static int stopmachine(void *cpu)
+{
+	int irqs_disabled = 0;
+	int prepared = 0;
+
+	set_cpus_allowed(current, cpumask_of_cpu((int)(long)cpu));
+
+	/* Ack: we are alive */
+	mb(); /* Theoretically the ack = 0 might not be on this CPU yet. */
+	atomic_inc(&stopmachine_thread_ack);
+
+	/* Simple state machine */
+	while (stopmachine_state != STOPMACHINE_EXIT) {
+		if (stopmachine_state == STOPMACHINE_DISABLE_IRQ 
+		    && !irqs_disabled) {
+			local_irq_disable();
+			irqs_disabled = 1;
+			/* Ack: irqs disabled. */
+			mb(); /* Must read state first. */
+			atomic_inc(&stopmachine_thread_ack);
+		} else if (stopmachine_state == STOPMACHINE_PREPARE
+			   && !prepared) {
+			/* Everyone is in place, hold CPU. */
+			preempt_disable();
+			prepared = 1;
+			mb(); /* Must read state first. */
+			atomic_inc(&stopmachine_thread_ack);
+		}
+		/* Yield in first stage: migration threads need to
+		 * help our sisters onto their CPUs. */
+		if (!prepared && !irqs_disabled)
+			yield();
+		else
+			cpu_relax();
+	}
+
+	/* Ack: we are exiting. */
+	mb(); /* Must read state first. */
+	atomic_inc(&stopmachine_thread_ack);
+
+	if (irqs_disabled)
+		local_irq_enable();
+	if (prepared)
+		preempt_enable();
+
+	return 0;
+}
+
+/* Change the thread state */
+static void stopmachine_set_state(enum stopmachine_state state)
+{
+	atomic_set(&stopmachine_thread_ack, 0);
+	wmb();
+	stopmachine_state = state;
+	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
+		cpu_relax();
+}
+
+static int stop_machine(void)
+{
+	int i, ret = 0;
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+	mm_segment_t old_fs = get_fs();
+
+	/* One high-prio thread per cpu.  We'll do this one. */
+	set_fs(KERNEL_DS);
+	sys_sched_setscheduler(current->pid, SCHED_FIFO,
+				(struct sched_param __user *)&param);
+	set_fs(old_fs);
+
+	atomic_set(&stopmachine_thread_ack, 0);
+	stopmachine_num_threads = 0;
+	stopmachine_state = STOPMACHINE_WAIT;
+
+	for_each_online_cpu(i) {
+		if (i == _smp_processor_id())
+			continue;
+		ret = kernel_thread(stopmachine, (void *)(long)i,CLONE_KERNEL);
+		if (ret < 0)
+			break;
+		stopmachine_num_threads++;
+	}
+
+	/* Wait for them all to come to life. */
+	while (atomic_read(&stopmachine_thread_ack) != stopmachine_num_threads)
+		yield();
+
+	/* If some failed, kill them all. */
+	if (ret < 0) {
+		stopmachine_set_state(STOPMACHINE_EXIT);
+		up(&stopmachine_mutex);
+		return ret;
+	}
+
+	/* Don't schedule us away at this point, please. */
+	local_irq_disable();
+
+	/* Now they are all started, make them hold the CPUs, ready. */
+	stopmachine_set_state(STOPMACHINE_PREPARE);
+
+	/* Make them disable irqs. */
+	stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
+
+	return 0;
+}
+
+static void restart_machine(void)
+{
+	stopmachine_set_state(STOPMACHINE_EXIT);
+	local_irq_enable();
+}
+
+struct stop_machine_data
+{
+	int (*fn)(void *);
+	void *data;
+	struct completion done;
+};
+
+static int do_stop(void *_smdata)
+{
+	struct stop_machine_data *smdata = _smdata;
+	int ret;
+
+	ret = stop_machine();
+	if (ret == 0) {
+		ret = smdata->fn(smdata->data);
+		restart_machine();
+	}
+
+	/* We're done: you can kthread_stop us now */
+	complete(&smdata->done);
+
+	/* Wait for kthread_stop */
+	set_current_state(TASK_INTERRUPTIBLE);
+	while (!kthread_should_stop()) {
+		schedule();
+		set_current_state(TASK_INTERRUPTIBLE);
+	}
+	__set_current_state(TASK_RUNNING);
+	return ret;
+}
+
+struct task_struct *__stop_machine_run(int (*fn)(void *), void *data,
+				       unsigned int cpu)
+{
+	struct stop_machine_data smdata;
+	struct task_struct *p;
+
+	smdata.fn = fn;
+	smdata.data = data;
+	init_completion(&smdata.done);
+
+	down(&stopmachine_mutex);
+
+	/* If they don't care which CPU fn runs on, bind to any online one. */
+	if (cpu == NR_CPUS)
+		cpu = _smp_processor_id();
+
+	p = kthread_create(do_stop, &smdata, "kstopmachine");
+	if (!IS_ERR(p)) {
+		kthread_bind(p, cpu);
+		wake_up_process(p);
+		wait_for_completion(&smdata.done);
+	}
+	up(&stopmachine_mutex);
+	return p;
+}
+
+int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
+{
+	struct task_struct *p;
+	int ret;
+
+	/* No CPUs can come up or down during this. */
+	lock_cpu_hotplug();
+	p = __stop_machine_run(fn, data, cpu);
+	if (!IS_ERR(p))
+		ret = kthread_stop(p);
+	else
+		ret = PTR_ERR(p);
+	unlock_cpu_hotplug();
+
+	return ret;
+}