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Merge up to 2.6.5

/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/kmod.h>		/* for hotplug_path */
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <asm/semaphore.h>

/* This protects CPUs going up and down... */
DECLARE_MUTEX(cpucontrol);

static struct notifier_block *cpu_chain;

/* Need to know about CPUs going up/down? */
int register_cpu_notifier(struct notifier_block *nb)
{
	int ret;

	if ((ret = down_interruptible(&cpucontrol)) != 0)
		return ret;
	ret = notifier_chain_register(&cpu_chain, nb);
	up(&cpucontrol);
	return ret;
}
EXPORT_SYMBOL(register_cpu_notifier);

void unregister_cpu_notifier(struct notifier_block *nb)
{
	down(&cpucontrol);
	notifier_chain_unregister(&cpu_chain, nb);
	up(&cpucontrol);
}
EXPORT_SYMBOL(unregister_cpu_notifier);

#ifdef CONFIG_HOTPLUG_CPU
static inline void check_for_tasks(int cpu, struct task_struct *k)
{
	struct task_struct *p;

	write_lock_irq(&tasklist_lock);
	for_each_process(p) {
		if (task_cpu(p) == cpu && p != k)
			printk(KERN_WARNING "Task %s is on cpu %d\n",
				p->comm, cpu);
	}
	write_unlock_irq(&tasklist_lock);
}

/* Notify userspace when a cpu event occurs, by running '/sbin/hotplug
 * cpu' with certain environment variables set.  */
static int cpu_run_sbin_hotplug(unsigned int cpu, const char *action)
{
	char *argv[3], *envp[5], cpu_str[12], action_str[32];
	int i;

	sprintf(cpu_str, "CPU=%d", cpu);
	sprintf(action_str, "ACTION=%s", action);
	/* FIXME: Add DEVPATH. --RR */

	i = 0;
	argv[i++] = hotplug_path;
	argv[i++] = "cpu";
	argv[i] = NULL;

	i = 0;
	/* minimal command environment */
	envp[i++] = "HOME=/";
	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
	envp[i++] = cpu_str;
	envp[i++] = action_str;
	envp[i] = NULL;

	return call_usermodehelper(argv[0], argv, envp, 0);
}

/* Take this CPU down. */
static int take_cpu_down(void *unused)
{
	int err;

	/* Take offline: makes arch_cpu_down somewhat easier. */
	cpu_clear(smp_processor_id(), cpu_online_map);

	/* Ensure this CPU doesn't handle any more interrupts. */
	err = __cpu_disable();
	if (err < 0)
		cpu_set(smp_processor_id(), cpu_online_map);
	else
		/* Everyone else gets kicked off. */
		migrate_all_tasks();

	return err;
}

int cpu_down(unsigned int cpu)
{
	int err;
	struct task_struct *p;

	if ((err = lock_cpu_hotplug_interruptible()) != 0)
		return err;

	if (num_online_cpus() == 1) {
		err = -EBUSY;
		goto out;
	}

	if (!cpu_online(cpu)) {
		err = -EINVAL;
		goto out;
	}

	p = __stop_machine_run(take_cpu_down, NULL, cpu);
	if (IS_ERR(p)) {
		err = PTR_ERR(p);
		goto out;
	}

	if (cpu_online(cpu))
		goto out_thread;

	check_for_tasks(cpu, p);

	/* Wait for it to sleep (leaving idle task). */
	while (!idle_cpu(cpu))
		yield();

	/* This actually kills the CPU. */
	__cpu_die(cpu);

	/* Move it here so it can run. */
	kthread_bind(p, smp_processor_id());

	/* CPU is completely dead: tell everyone.  Too late to complain. */
	if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
	    == NOTIFY_BAD)
		BUG();

	cpu_run_sbin_hotplug(cpu, "offline");

out_thread:
	err = kthread_stop(p);
out:
	unlock_cpu_hotplug();
	return err;
}
#else
static inline int cpu_run_sbin_hotplug(unsigned int cpu, const char *action)
{
	return 0;
}
#endif /*CONFIG_HOTPLUG_CPU*/

int __devinit cpu_up(unsigned int cpu)
{
	int ret;
	void *hcpu = (void *)(long)cpu;

	if ((ret = down_interruptible(&cpucontrol)) != 0)
		return ret;

	if (cpu_online(cpu)) {
		ret = -EINVAL;
		goto out;
	}
	ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
	if (ret == NOTIFY_BAD) {
		printk("%s: attempt to bring up CPU %u failed\n",
				__FUNCTION__, cpu);
		ret = -EINVAL;
		goto out_notify;
	}

	/* Arch-specific enabling code. */
	ret = __cpu_up(cpu);
	if (ret != 0)
		goto out_notify;
	if (!cpu_online(cpu))
		BUG();

	/* Now call notifier in preparation. */
	notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);

out_notify:
	if (ret != 0)
		notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
out:
	up(&cpucontrol);
	return ret;
}