kernel/cpu.c - maze/linux - Git at Google

 /* 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/kthread.h>
 #include <linux/stop_machine.h>
 #include <linux/mutex.h>

 /*
  * Represents all cpu's present in the system
  * In systems capable of hotplug, this map could dynamically grow
  * as new cpu's are detected in the system via any platform specific
  * method, such as ACPI for e.g.
  */
 cpumask_t cpu_present_map __read_mostly;
 EXPORT_SYMBOL(cpu_present_map);

 #ifndef CONFIG_SMP

 /*
  * Represents all cpu's that are currently online.
  */
 cpumask_t cpu_online_map __read_mostly = CPU_MASK_ALL;
 EXPORT_SYMBOL(cpu_online_map);

 cpumask_t cpu_possible_map __read_mostly = CPU_MASK_ALL;
 EXPORT_SYMBOL(cpu_possible_map);

 #else /* CONFIG_SMP */

 /* Serializes the updates to cpu_online_map, cpu_present_map */
 static DEFINE_MUTEX(cpu_add_remove_lock);

 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);

 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  * Should always be manipulated under cpu_add_remove_lock
  */
 static int cpu_hotplug_disabled;

 static struct {
 	struct task_struct *active_writer;
 	struct mutex lock; /* Synchronizes accesses to refcount, */
 	/*
 	 * Also blocks the new readers during
 	 * an ongoing cpu hotplug operation.
 	 */
 	int refcount;
 } cpu_hotplug;

 void __init cpu_hotplug_init(void)
 {
 	cpu_hotplug.active_writer = NULL;
 	mutex_init(&cpu_hotplug.lock);
 	cpu_hotplug.refcount = 0;
 }

 cpumask_t cpu_active_map;

 #ifdef CONFIG_HOTPLUG_CPU

 void get_online_cpus(void)
 {
 	might_sleep();
 	if (cpu_hotplug.active_writer == current)
 		return;
 	mutex_lock(&cpu_hotplug.lock);
 	cpu_hotplug.refcount++;
 	mutex_unlock(&cpu_hotplug.lock);

 }
 EXPORT_SYMBOL_GPL(get_online_cpus);

 void put_online_cpus(void)
 {
 	if (cpu_hotplug.active_writer == current)
 		return;
 	mutex_lock(&cpu_hotplug.lock);
 	if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
 		wake_up_process(cpu_hotplug.active_writer);
 	mutex_unlock(&cpu_hotplug.lock);

 }
 EXPORT_SYMBOL_GPL(put_online_cpus);

 #endif	/* CONFIG_HOTPLUG_CPU */

 /*
  * The following two API's must be used when attempting
  * to serialize the updates to cpu_online_map, cpu_present_map.
  */
 void cpu_maps_update_begin(void)
 {
 	mutex_lock(&cpu_add_remove_lock);
 }

 void cpu_maps_update_done(void)
 {
 	mutex_unlock(&cpu_add_remove_lock);
 }

 /*
  * This ensures that the hotplug operation can begin only when the
  * refcount goes to zero.
  *
  * Note that during a cpu-hotplug operation, the new readers, if any,
  * will be blocked by the cpu_hotplug.lock
  *
  * Since cpu_hotplug_begin() is always called after invoking
  * cpu_maps_update_begin(), we can be sure that only one writer is active.
  *
  * Note that theoretically, there is a possibility of a livelock:
  * - Refcount goes to zero, last reader wakes up the sleeping
  *   writer.
  * - Last reader unlocks the cpu_hotplug.lock.
  * - A new reader arrives at this moment, bumps up the refcount.
  * - The writer acquires the cpu_hotplug.lock finds the refcount
  *   non zero and goes to sleep again.
  *
  * However, this is very difficult to achieve in practice since
  * get_online_cpus() not an api which is called all that often.
  *
  */
 static void cpu_hotplug_begin(void)
 {
 	cpu_hotplug.active_writer = current;

 	for (;;) {
 		mutex_lock(&cpu_hotplug.lock);
 		if (likely(!cpu_hotplug.refcount))
 			break;
 		__set_current_state(TASK_UNINTERRUPTIBLE);
 		mutex_unlock(&cpu_hotplug.lock);
 		schedule();
 	}
 }

 static void cpu_hotplug_done(void)
 {
 	cpu_hotplug.active_writer = NULL;
 	mutex_unlock(&cpu_hotplug.lock);
 }
 /* Need to know about CPUs going up/down? */
 int __ref register_cpu_notifier(struct notifier_block *nb)
 {
 	int ret;
 	cpu_maps_update_begin();
 	ret = raw_notifier_chain_register(&cpu_chain, nb);
 	cpu_maps_update_done();
 	return ret;
 }

 #ifdef CONFIG_HOTPLUG_CPU

 EXPORT_SYMBOL(register_cpu_notifier);

 void __ref unregister_cpu_notifier(struct notifier_block *nb)
 {
 	cpu_maps_update_begin();
 	raw_notifier_chain_unregister(&cpu_chain, nb);
 	cpu_maps_update_done();
 }
 EXPORT_SYMBOL(unregister_cpu_notifier);

 static inline void check_for_tasks(int cpu)
 {
 	struct task_struct *p;

 	write_lock_irq(&tasklist_lock);
 	for_each_process(p) {
 		if (task_cpu(p) == cpu &&
 		    (!cputime_eq(p->utime, cputime_zero) ||
 		     !cputime_eq(p->stime, cputime_zero)))
 			printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 				(state = %ld, flags = %x) \n",
 				 p->comm, task_pid_nr(p), cpu,
 				 p->state, p->flags);
 	}
 	write_unlock_irq(&tasklist_lock);
 }

 struct take_cpu_down_param {
 	unsigned long mod;
 	void *hcpu;
 };

 /* Take this CPU down. */
 static int __ref take_cpu_down(void *_param)
 {
 	struct take_cpu_down_param *param = _param;
 	int err;

 	raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 				param->hcpu);
 	/* Ensure this CPU doesn't handle any more interrupts. */
 	err = __cpu_disable();
 	if (err < 0)
 		return err;

 	/* Force idle task to run as soon as we yield: it should
 	   immediately notice cpu is offline and die quickly. */
 	sched_idle_next();
 	return 0;
 }

 /* Requires cpu_add_remove_lock to be held */
 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 {
 	int err, nr_calls = 0;
 	cpumask_t old_allowed, tmp;
 	void *hcpu = (void *)(long)cpu;
 	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 	struct take_cpu_down_param tcd_param = {
 		.mod = mod,
 		.hcpu = hcpu,
 	};

 	if (num_online_cpus() == 1)
 		return -EBUSY;

 	if (!cpu_online(cpu))
 		return -EINVAL;

 	cpu_hotplug_begin();
 	err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 					hcpu, -1, &nr_calls);
 	if (err == NOTIFY_BAD) {
 		nr_calls--;
 		__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 					  hcpu, nr_calls, NULL);
 		printk("%s: attempt to take down CPU %u failed\n",
 				__func__, cpu);
 		err = -EINVAL;
 		goto out_release;
 	}

 	/* Ensure that we are not runnable on dying cpu */
 	old_allowed = current->cpus_allowed;
 	cpus_setall(tmp);
 	cpu_clear(cpu, tmp);
 	set_cpus_allowed_ptr(current, &tmp);
 	tmp = cpumask_of_cpu(cpu);

 	err = __stop_machine(take_cpu_down, &tcd_param, &tmp);
 	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
 		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 					    hcpu) == NOTIFY_BAD)
 			BUG();

 		goto out_allowed;
 	}
 	BUG_ON(cpu_online(cpu));

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

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

 	/* CPU is completely dead: tell everyone.  Too late to complain. */
 	if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 				    hcpu) == NOTIFY_BAD)
 		BUG();

 	check_for_tasks(cpu);

 out_allowed:
 	set_cpus_allowed_ptr(current, &old_allowed);
 out_release:
 	cpu_hotplug_done();
 	if (!err) {
 		if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 					    hcpu) == NOTIFY_BAD)
 			BUG();
 	}
 	return err;
 }

 int __ref cpu_down(unsigned int cpu)
 {
 	int err = 0;

 	cpu_maps_update_begin();

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

 	cpu_clear(cpu, cpu_active_map);

 	/*
 	 * Make sure the all cpus did the reschedule and are not
 	 * using stale version of the cpu_active_map.
 	 * This is not strictly necessary becuase stop_machine()
 	 * that we run down the line already provides the required
 	 * synchronization. But it's really a side effect and we do not
 	 * want to depend on the innards of the stop_machine here.
 	 */
 	synchronize_sched();

 	err = _cpu_down(cpu, 0);

 	if (cpu_online(cpu))
 		cpu_set(cpu, cpu_active_map);

 out:
 	cpu_maps_update_done();
 	return err;
 }
 EXPORT_SYMBOL(cpu_down);
 #endif /*CONFIG_HOTPLUG_CPU*/

 /* Requires cpu_add_remove_lock to be held */
 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 {
 	int ret, nr_calls = 0;
 	void *hcpu = (void *)(long)cpu;
 	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;

 	if (cpu_online(cpu) || !cpu_present(cpu))
 		return -EINVAL;

 	cpu_hotplug_begin();
 	ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 							-1, &nr_calls);
 	if (ret == NOTIFY_BAD) {
 		nr_calls--;
 		printk("%s: attempt to bring up CPU %u failed\n",
 				__func__, cpu);
 		ret = -EINVAL;
 		goto out_notify;
 	}

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

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

 out_notify:
 	if (ret != 0)
 		__raw_notifier_call_chain(&cpu_chain,
 				CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 	cpu_hotplug_done();

 	return ret;
 }

 int __cpuinit cpu_up(unsigned int cpu)
 {
 	int err = 0;
 	if (!cpu_isset(cpu, cpu_possible_map)) {
 		printk(KERN_ERR "can't online cpu %d because it is not "
 			"configured as may-hotadd at boot time\n", cpu);
 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
 		printk(KERN_ERR "please check additional_cpus= boot "
 				"parameter\n");
 #endif
 		return -EINVAL;
 	}

 	cpu_maps_update_begin();

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

 	err = _cpu_up(cpu, 0);

 	if (cpu_online(cpu))
 		cpu_set(cpu, cpu_active_map);

 out:
 	cpu_maps_update_done();
 	return err;
 }

 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_t frozen_cpus;

 int disable_nonboot_cpus(void)
 {
 	int cpu, first_cpu, error = 0;

 	cpu_maps_update_begin();
 	first_cpu = first_cpu(cpu_online_map);
 	/* We take down all of the non-boot CPUs in one shot to avoid races
 	 * with the userspace trying to use the CPU hotplug at the same time
 	 */
 	cpus_clear(frozen_cpus);
 	printk("Disabling non-boot CPUs ...\n");
 	for_each_online_cpu(cpu) {
 		if (cpu == first_cpu)
 			continue;
 		error = _cpu_down(cpu, 1);
 		if (!error) {
 			cpu_set(cpu, frozen_cpus);
 			printk("CPU%d is down\n", cpu);
 		} else {
 			printk(KERN_ERR "Error taking CPU%d down: %d\n",
 				cpu, error);
 			break;
 		}
 	}
 	if (!error) {
 		BUG_ON(num_online_cpus() > 1);
 		/* Make sure the CPUs won't be enabled by someone else */
 		cpu_hotplug_disabled = 1;
 	} else {
 		printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 	}
 	cpu_maps_update_done();
 	return error;
 }

 void __ref enable_nonboot_cpus(void)
 {
 	int cpu, error;

 	/* Allow everyone to use the CPU hotplug again */
 	cpu_maps_update_begin();
 	cpu_hotplug_disabled = 0;
 	if (cpus_empty(frozen_cpus))
 		goto out;

 	printk("Enabling non-boot CPUs ...\n");
 	for_each_cpu_mask_nr(cpu, frozen_cpus) {
 		error = _cpu_up(cpu, 1);
 		if (!error) {
 			printk("CPU%d is up\n", cpu);
 			continue;
 		}
 		printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 	}
 	cpus_clear(frozen_cpus);
 out:
 	cpu_maps_update_done();
 }
 #endif /* CONFIG_PM_SLEEP_SMP */

 #endif /* CONFIG_SMP */

 /*
  * cpu_bit_bitmap[] is a special, "compressed" data structure that
  * represents all NR_CPUS bits binary values of 1<<nr.
  *
  * It is used by cpumask_of_cpu() to get a constant address to a CPU
  * mask value that has a single bit set only.
  */

 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 #define MASK_DECLARE_1(x)	[x+1][0] = 1UL << (x)
 #define MASK_DECLARE_2(x)	MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 #define MASK_DECLARE_4(x)	MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 #define MASK_DECLARE_8(x)	MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)

 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {

 	MASK_DECLARE_8(0),	MASK_DECLARE_8(8),
 	MASK_DECLARE_8(16),	MASK_DECLARE_8(24),
 #if BITS_PER_LONG > 32
 	MASK_DECLARE_8(32),	MASK_DECLARE_8(40),
 	MASK_DECLARE_8(48),	MASK_DECLARE_8(56),
 #endif
 };
 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
	/* 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/kthread.h>
	#include <linux/stop_machine.h>
	#include <linux/mutex.h>

	/*
	* Represents all cpu's present in the system
	* In systems capable of hotplug, this map could dynamically grow
	* as new cpu's are detected in the system via any platform specific
	* method, such as ACPI for e.g.
	*/
	cpumask_t cpu_present_map __read_mostly;
	EXPORT_SYMBOL(cpu_present_map);

	#ifndef CONFIG_SMP

	/*
	* Represents all cpu's that are currently online.
	*/
	cpumask_t cpu_online_map __read_mostly = CPU_MASK_ALL;
	EXPORT_SYMBOL(cpu_online_map);

	cpumask_t cpu_possible_map __read_mostly = CPU_MASK_ALL;
	EXPORT_SYMBOL(cpu_possible_map);

	#else /* CONFIG_SMP */

	/* Serializes the updates to cpu_online_map, cpu_present_map */
	static DEFINE_MUTEX(cpu_add_remove_lock);

	static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);

	/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
	* Should always be manipulated under cpu_add_remove_lock
	*/
	static int cpu_hotplug_disabled;

	static struct {
	struct task_struct *active_writer;
	struct mutex lock; /* Synchronizes accesses to refcount, */
	/*
	* Also blocks the new readers during
	* an ongoing cpu hotplug operation.
	*/
	int refcount;
	} cpu_hotplug;

	void __init cpu_hotplug_init(void)
	{
	cpu_hotplug.active_writer = NULL;
	mutex_init(&cpu_hotplug.lock);
	cpu_hotplug.refcount = 0;
	}

	cpumask_t cpu_active_map;

	#ifdef CONFIG_HOTPLUG_CPU

	void get_online_cpus(void)
	{
	might_sleep();
	if (cpu_hotplug.active_writer == current)
	return;
	mutex_lock(&cpu_hotplug.lock);
	cpu_hotplug.refcount++;
	mutex_unlock(&cpu_hotplug.lock);

	}
	EXPORT_SYMBOL_GPL(get_online_cpus);

	void put_online_cpus(void)
	{
	if (cpu_hotplug.active_writer == current)
	return;
	mutex_lock(&cpu_hotplug.lock);
	if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
	wake_up_process(cpu_hotplug.active_writer);
	mutex_unlock(&cpu_hotplug.lock);

	}
	EXPORT_SYMBOL_GPL(put_online_cpus);

	#endif /* CONFIG_HOTPLUG_CPU */

	/*
	* The following two API's must be used when attempting
	* to serialize the updates to cpu_online_map, cpu_present_map.
	*/
	void cpu_maps_update_begin(void)
	{
	mutex_lock(&cpu_add_remove_lock);
	}

	void cpu_maps_update_done(void)
	{
	mutex_unlock(&cpu_add_remove_lock);
	}

	/*
	* This ensures that the hotplug operation can begin only when the
	* refcount goes to zero.
	*
	* Note that during a cpu-hotplug operation, the new readers, if any,
	* will be blocked by the cpu_hotplug.lock
	*
	* Since cpu_hotplug_begin() is always called after invoking
	* cpu_maps_update_begin(), we can be sure that only one writer is active.
	*
	* Note that theoretically, there is a possibility of a livelock:
	* - Refcount goes to zero, last reader wakes up the sleeping
	* writer.
	* - Last reader unlocks the cpu_hotplug.lock.
	* - A new reader arrives at this moment, bumps up the refcount.
	* - The writer acquires the cpu_hotplug.lock finds the refcount
	* non zero and goes to sleep again.
	*
	* However, this is very difficult to achieve in practice since
	* get_online_cpus() not an api which is called all that often.
	*
	*/
	static void cpu_hotplug_begin(void)
	{
	cpu_hotplug.active_writer = current;

	for (;;) {
	mutex_lock(&cpu_hotplug.lock);
	if (likely(!cpu_hotplug.refcount))
	break;
	__set_current_state(TASK_UNINTERRUPTIBLE);
	mutex_unlock(&cpu_hotplug.lock);
	schedule();
	}
	}

	static void cpu_hotplug_done(void)
	{
	cpu_hotplug.active_writer = NULL;
	mutex_unlock(&cpu_hotplug.lock);
	}
	/* Need to know about CPUs going up/down? */
	int __ref register_cpu_notifier(struct notifier_block *nb)
	{
	int ret;
	cpu_maps_update_begin();
	ret = raw_notifier_chain_register(&cpu_chain, nb);
	cpu_maps_update_done();
	return ret;
	}

	#ifdef CONFIG_HOTPLUG_CPU

	EXPORT_SYMBOL(register_cpu_notifier);

	void __ref unregister_cpu_notifier(struct notifier_block *nb)
	{
	cpu_maps_update_begin();
	raw_notifier_chain_unregister(&cpu_chain, nb);
	cpu_maps_update_done();
	}
	EXPORT_SYMBOL(unregister_cpu_notifier);

	static inline void check_for_tasks(int cpu)
	{
	struct task_struct *p;

	write_lock_irq(&tasklist_lock);
	for_each_process(p) {
	if (task_cpu(p) == cpu &&
	(!cputime_eq(p->utime, cputime_zero) \|\|
	!cputime_eq(p->stime, cputime_zero)))
	printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
	(state = %ld, flags = %x) \n",
	p->comm, task_pid_nr(p), cpu,
	p->state, p->flags);
	}
	write_unlock_irq(&tasklist_lock);
	}

	struct take_cpu_down_param {
	unsigned long mod;
	void *hcpu;
	};

	/* Take this CPU down. */
	static int __ref take_cpu_down(void *_param)
	{
	struct take_cpu_down_param *param = _param;
	int err;

	raw_notifier_call_chain(&cpu_chain, CPU_DYING \| param->mod,
	param->hcpu);
	/* Ensure this CPU doesn't handle any more interrupts. */
	err = __cpu_disable();
	if (err < 0)
	return err;

	/* Force idle task to run as soon as we yield: it should
	immediately notice cpu is offline and die quickly. */
	sched_idle_next();
	return 0;
	}

	/* Requires cpu_add_remove_lock to be held */
	static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
	{
	int err, nr_calls = 0;
	cpumask_t old_allowed, tmp;
	void hcpu = (void )(long)cpu;
	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
	struct take_cpu_down_param tcd_param = {
	.mod = mod,
	.hcpu = hcpu,
	};

	if (num_online_cpus() == 1)
	return -EBUSY;

	if (!cpu_online(cpu))
	return -EINVAL;

	cpu_hotplug_begin();
	err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE \| mod,
	hcpu, -1, &nr_calls);
	if (err == NOTIFY_BAD) {
	nr_calls--;
	__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED \| mod,
	hcpu, nr_calls, NULL);
	printk("%s: attempt to take down CPU %u failed\n",
	__func__, cpu);
	err = -EINVAL;
	goto out_release;
	}

	/* Ensure that we are not runnable on dying cpu */
	old_allowed = current->cpus_allowed;
	cpus_setall(tmp);
	cpu_clear(cpu, tmp);
	set_cpus_allowed_ptr(current, &tmp);
	tmp = cpumask_of_cpu(cpu);

	err = __stop_machine(take_cpu_down, &tcd_param, &tmp);
	if (err) {
	/* CPU didn't die: tell everyone. Can't complain. */
	if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED \| mod,
	hcpu) == NOTIFY_BAD)
	BUG();

	goto out_allowed;
	}
	BUG_ON(cpu_online(cpu));

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

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

	/* CPU is completely dead: tell everyone. Too late to complain. */
	if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD \| mod,
	hcpu) == NOTIFY_BAD)
	BUG();

	check_for_tasks(cpu);

	out_allowed:
	set_cpus_allowed_ptr(current, &old_allowed);
	out_release:
	cpu_hotplug_done();
	if (!err) {
	if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD \| mod,
	hcpu) == NOTIFY_BAD)
	BUG();
	}
	return err;
	}

	int __ref cpu_down(unsigned int cpu)
	{
	int err = 0;

	cpu_maps_update_begin();

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

	cpu_clear(cpu, cpu_active_map);

	/*
	* Make sure the all cpus did the reschedule and are not
	* using stale version of the cpu_active_map.
	* This is not strictly necessary becuase stop_machine()
	* that we run down the line already provides the required
	* synchronization. But it's really a side effect and we do not
	* want to depend on the innards of the stop_machine here.
	*/
	synchronize_sched();

	err = _cpu_down(cpu, 0);

	if (cpu_online(cpu))
	cpu_set(cpu, cpu_active_map);

	out:
	cpu_maps_update_done();
	return err;
	}
	EXPORT_SYMBOL(cpu_down);
	#endif /CONFIG_HOTPLUG_CPU/

	/* Requires cpu_add_remove_lock to be held */
	static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
	{
	int ret, nr_calls = 0;
	void hcpu = (void )(long)cpu;
	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;

	if (cpu_online(cpu) \|\| !cpu_present(cpu))
	return -EINVAL;

	cpu_hotplug_begin();
	ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE \| mod, hcpu,
	-1, &nr_calls);
	if (ret == NOTIFY_BAD) {
	nr_calls--;
	printk("%s: attempt to bring up CPU %u failed\n",
	__func__, cpu);
	ret = -EINVAL;
	goto out_notify;
	}

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

	/* Now call notifier in preparation. */
	raw_notifier_call_chain(&cpu_chain, CPU_ONLINE \| mod, hcpu);

	out_notify:
	if (ret != 0)
	__raw_notifier_call_chain(&cpu_chain,
	CPU_UP_CANCELED \| mod, hcpu, nr_calls, NULL);
	cpu_hotplug_done();

	return ret;
	}

	int __cpuinit cpu_up(unsigned int cpu)
	{
	int err = 0;
	if (!cpu_isset(cpu, cpu_possible_map)) {
	printk(KERN_ERR "can't online cpu %d because it is not "
	"configured as may-hotadd at boot time\n", cpu);
	#if defined(CONFIG_IA64) \|\| defined(CONFIG_X86_64) \|\| defined(CONFIG_S390)
	printk(KERN_ERR "please check additional_cpus= boot "
	"parameter\n");
	#endif
	return -EINVAL;
	}

	cpu_maps_update_begin();

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

	err = _cpu_up(cpu, 0);

	if (cpu_online(cpu))
	cpu_set(cpu, cpu_active_map);

	out:
	cpu_maps_update_done();
	return err;
	}

	#ifdef CONFIG_PM_SLEEP_SMP
	static cpumask_t frozen_cpus;

	int disable_nonboot_cpus(void)
	{
	int cpu, first_cpu, error = 0;

	cpu_maps_update_begin();
	first_cpu = first_cpu(cpu_online_map);
	/* We take down all of the non-boot CPUs in one shot to avoid races
	* with the userspace trying to use the CPU hotplug at the same time
	*/
	cpus_clear(frozen_cpus);
	printk("Disabling non-boot CPUs ...\n");
	for_each_online_cpu(cpu) {
	if (cpu == first_cpu)
	continue;
	error = _cpu_down(cpu, 1);
	if (!error) {
	cpu_set(cpu, frozen_cpus);
	printk("CPU%d is down\n", cpu);
	} else {
	printk(KERN_ERR "Error taking CPU%d down: %d\n",
	cpu, error);
	break;
	}
	}
	if (!error) {
	BUG_ON(num_online_cpus() > 1);
	/* Make sure the CPUs won't be enabled by someone else */
	cpu_hotplug_disabled = 1;
	} else {
	printk(KERN_ERR "Non-boot CPUs are not disabled\n");
	}
	cpu_maps_update_done();
	return error;
	}

	void __ref enable_nonboot_cpus(void)
	{
	int cpu, error;

	/* Allow everyone to use the CPU hotplug again */
	cpu_maps_update_begin();
	cpu_hotplug_disabled = 0;
	if (cpus_empty(frozen_cpus))
	goto out;

	printk("Enabling non-boot CPUs ...\n");
	for_each_cpu_mask_nr(cpu, frozen_cpus) {
	error = _cpu_up(cpu, 1);
	if (!error) {
	printk("CPU%d is up\n", cpu);
	continue;
	}
	printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
	}
	cpus_clear(frozen_cpus);
	out:
	cpu_maps_update_done();
	}
	#endif /* CONFIG_PM_SLEEP_SMP */

	#endif /* CONFIG_SMP */

	/*
	* cpu_bit_bitmap[] is a special, "compressed" data structure that
	* represents all NR_CPUS bits binary values of 1<<nr.
	*
	* It is used by cpumask_of_cpu() to get a constant address to a CPU
	* mask value that has a single bit set only.
	*/

	/* cpu_bit_bitmap[0] is empty - so we can back into it */
	#define MASK_DECLARE_1(x) [x+1][0] = 1UL << (x)
	#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
	#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
	#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)

	const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {

	MASK_DECLARE_8(0), MASK_DECLARE_8(8),
	MASK_DECLARE_8(16), MASK_DECLARE_8(24),
	#if BITS_PER_LONG > 32
	MASK_DECLARE_8(32), MASK_DECLARE_8(40),
	MASK_DECLARE_8(48), MASK_DECLARE_8(56),
	#endif
	};
	EXPORT_SYMBOL_GPL(cpu_bit_bitmap);