2 * (C) 2001, 2002, 2003, 2004 Rusty Russell
4 * This code is licenced under the GPL.
6 #include <linux/proc_fs.h>
8 #include <linux/init.h>
9 #include <linux/notifier.h>
10 #include <linux/sched.h>
11 #include <linux/unistd.h>
12 #include <linux/cpu.h>
13 #include <linux/oom.h>
14 #include <linux/rcupdate.h>
15 #include <linux/export.h>
16 #include <linux/bug.h>
17 #include <linux/kthread.h>
18 #include <linux/stop_machine.h>
19 #include <linux/mutex.h>
20 #include <linux/gfp.h>
21 #include <linux/suspend.h>
22 #include <linux/lockdep.h>
23 #include <linux/tick.h>
24 #include <linux/irq.h>
25 #include <trace/events/power.h>
27 #include <trace/events/sched.h>
32 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
33 static DEFINE_MUTEX(cpu_add_remove_lock);
36 * The following two APIs (cpu_maps_update_begin/done) must be used when
37 * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
38 * The APIs cpu_notifier_register_begin/done() must be used to protect CPU
39 * hotplug callback (un)registration performed using __register_cpu_notifier()
40 * or __unregister_cpu_notifier().
42 void cpu_maps_update_begin(void)
44 mutex_lock(&cpu_add_remove_lock);
46 EXPORT_SYMBOL(cpu_notifier_register_begin);
48 void cpu_maps_update_done(void)
50 mutex_unlock(&cpu_add_remove_lock);
52 EXPORT_SYMBOL(cpu_notifier_register_done);
54 static RAW_NOTIFIER_HEAD(cpu_chain);
56 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
57 * Should always be manipulated under cpu_add_remove_lock
59 static int cpu_hotplug_disabled;
61 #ifdef CONFIG_HOTPLUG_CPU
64 struct task_struct *active_writer;
65 /* wait queue to wake up the active_writer */
67 /* verifies that no writer will get active while readers are active */
70 * Also blocks the new readers during
71 * an ongoing cpu hotplug operation.
75 #ifdef CONFIG_DEBUG_LOCK_ALLOC
76 struct lockdep_map dep_map;
79 .active_writer = NULL,
80 .wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
81 .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
82 #ifdef CONFIG_DEBUG_LOCK_ALLOC
83 .dep_map = {.name = "cpu_hotplug.lock" },
87 /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
88 #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
89 #define cpuhp_lock_acquire_tryread() \
90 lock_map_acquire_tryread(&cpu_hotplug.dep_map)
91 #define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map)
92 #define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map)
95 void get_online_cpus(void)
98 if (cpu_hotplug.active_writer == current)
100 cpuhp_lock_acquire_read();
101 mutex_lock(&cpu_hotplug.lock);
102 atomic_inc(&cpu_hotplug.refcount);
103 mutex_unlock(&cpu_hotplug.lock);
105 EXPORT_SYMBOL_GPL(get_online_cpus);
107 void put_online_cpus(void)
111 if (cpu_hotplug.active_writer == current)
114 refcount = atomic_dec_return(&cpu_hotplug.refcount);
115 if (WARN_ON(refcount < 0)) /* try to fix things up */
116 atomic_inc(&cpu_hotplug.refcount);
118 if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
119 wake_up(&cpu_hotplug.wq);
121 cpuhp_lock_release();
124 EXPORT_SYMBOL_GPL(put_online_cpus);
127 * This ensures that the hotplug operation can begin only when the
128 * refcount goes to zero.
130 * Note that during a cpu-hotplug operation, the new readers, if any,
131 * will be blocked by the cpu_hotplug.lock
133 * Since cpu_hotplug_begin() is always called after invoking
134 * cpu_maps_update_begin(), we can be sure that only one writer is active.
136 * Note that theoretically, there is a possibility of a livelock:
137 * - Refcount goes to zero, last reader wakes up the sleeping
139 * - Last reader unlocks the cpu_hotplug.lock.
140 * - A new reader arrives at this moment, bumps up the refcount.
141 * - The writer acquires the cpu_hotplug.lock finds the refcount
142 * non zero and goes to sleep again.
144 * However, this is very difficult to achieve in practice since
145 * get_online_cpus() not an api which is called all that often.
148 void cpu_hotplug_begin(void)
152 cpu_hotplug.active_writer = current;
153 cpuhp_lock_acquire();
156 mutex_lock(&cpu_hotplug.lock);
157 prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
158 if (likely(!atomic_read(&cpu_hotplug.refcount)))
160 mutex_unlock(&cpu_hotplug.lock);
163 finish_wait(&cpu_hotplug.wq, &wait);
166 void cpu_hotplug_done(void)
168 cpu_hotplug.active_writer = NULL;
169 mutex_unlock(&cpu_hotplug.lock);
170 cpuhp_lock_release();
174 * Wait for currently running CPU hotplug operations to complete (if any) and
175 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
176 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
177 * hotplug path before performing hotplug operations. So acquiring that lock
178 * guarantees mutual exclusion from any currently running hotplug operations.
180 void cpu_hotplug_disable(void)
182 cpu_maps_update_begin();
183 cpu_hotplug_disabled++;
184 cpu_maps_update_done();
186 EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
188 void cpu_hotplug_enable(void)
190 cpu_maps_update_begin();
191 WARN_ON(--cpu_hotplug_disabled < 0);
192 cpu_maps_update_done();
194 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
195 #endif /* CONFIG_HOTPLUG_CPU */
197 /* Need to know about CPUs going up/down? */
198 int register_cpu_notifier(struct notifier_block *nb)
201 cpu_maps_update_begin();
202 ret = raw_notifier_chain_register(&cpu_chain, nb);
203 cpu_maps_update_done();
207 int __register_cpu_notifier(struct notifier_block *nb)
209 return raw_notifier_chain_register(&cpu_chain, nb);
212 static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
217 ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
220 return notifier_to_errno(ret);
223 static int cpu_notify(unsigned long val, void *v)
225 return __cpu_notify(val, v, -1, NULL);
228 #ifdef CONFIG_HOTPLUG_CPU
230 static void cpu_notify_nofail(unsigned long val, void *v)
232 BUG_ON(cpu_notify(val, v));
234 EXPORT_SYMBOL(register_cpu_notifier);
235 EXPORT_SYMBOL(__register_cpu_notifier);
237 void unregister_cpu_notifier(struct notifier_block *nb)
239 cpu_maps_update_begin();
240 raw_notifier_chain_unregister(&cpu_chain, nb);
241 cpu_maps_update_done();
243 EXPORT_SYMBOL(unregister_cpu_notifier);
245 void __unregister_cpu_notifier(struct notifier_block *nb)
247 raw_notifier_chain_unregister(&cpu_chain, nb);
249 EXPORT_SYMBOL(__unregister_cpu_notifier);
252 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
255 * This function walks all processes, finds a valid mm struct for each one and
256 * then clears a corresponding bit in mm's cpumask. While this all sounds
257 * trivial, there are various non-obvious corner cases, which this function
258 * tries to solve in a safe manner.
260 * Also note that the function uses a somewhat relaxed locking scheme, so it may
261 * be called only for an already offlined CPU.
263 void clear_tasks_mm_cpumask(int cpu)
265 struct task_struct *p;
268 * This function is called after the cpu is taken down and marked
269 * offline, so its not like new tasks will ever get this cpu set in
270 * their mm mask. -- Peter Zijlstra
271 * Thus, we may use rcu_read_lock() here, instead of grabbing
272 * full-fledged tasklist_lock.
274 WARN_ON(cpu_online(cpu));
276 for_each_process(p) {
277 struct task_struct *t;
280 * Main thread might exit, but other threads may still have
281 * a valid mm. Find one.
283 t = find_lock_task_mm(p);
286 cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
292 static inline void check_for_tasks(int dead_cpu)
294 struct task_struct *g, *p;
296 read_lock(&tasklist_lock);
297 for_each_process_thread(g, p) {
301 * We do the check with unlocked task_rq(p)->lock.
302 * Order the reading to do not warn about a task,
303 * which was running on this cpu in the past, and
304 * it's just been woken on another cpu.
307 if (task_cpu(p) != dead_cpu)
310 pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
311 p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
313 read_unlock(&tasklist_lock);
316 struct take_cpu_down_param {
321 /* Take this CPU down. */
322 static int take_cpu_down(void *_param)
324 struct take_cpu_down_param *param = _param;
327 /* Ensure this CPU doesn't handle any more interrupts. */
328 err = __cpu_disable();
332 cpu_notify(CPU_DYING | param->mod, param->hcpu);
333 /* Give up timekeeping duties */
334 tick_handover_do_timer();
335 /* Park the stopper thread */
336 stop_machine_park((long)param->hcpu);
340 /* Requires cpu_add_remove_lock to be held */
341 static int _cpu_down(unsigned int cpu, int tasks_frozen)
343 int err, nr_calls = 0;
344 void *hcpu = (void *)(long)cpu;
345 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
346 struct take_cpu_down_param tcd_param = {
351 if (num_online_cpus() == 1)
354 if (!cpu_online(cpu))
359 err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
362 __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
363 pr_warn("%s: attempt to take down CPU %u failed\n",
369 * By now we've cleared cpu_active_mask, wait for all preempt-disabled
370 * and RCU users of this state to go away such that all new such users
373 * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
374 * not imply sync_sched(), so wait for both.
376 * Do sync before park smpboot threads to take care the rcu boost case.
378 if (IS_ENABLED(CONFIG_PREEMPT))
379 synchronize_rcu_mult(call_rcu, call_rcu_sched);
383 smpboot_park_threads(cpu);
386 * Prevent irq alloc/free while the dying cpu reorganizes the
387 * interrupt affinities.
392 * So now all preempt/rcu users must observe !cpu_active().
394 err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
396 /* CPU didn't die: tell everyone. Can't complain. */
397 cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
401 BUG_ON(cpu_online(cpu));
404 * The migration_call() CPU_DYING callback will have removed all
405 * runnable tasks from the cpu, there's only the idle task left now
406 * that the migration thread is done doing the stop_machine thing.
408 * Wait for the stop thread to go away.
410 while (!per_cpu(cpu_dead_idle, cpu))
412 smp_mb(); /* Read from cpu_dead_idle before __cpu_die(). */
413 per_cpu(cpu_dead_idle, cpu) = false;
415 /* Interrupts are moved away from the dying cpu, reenable alloc/free */
418 hotplug_cpu__broadcast_tick_pull(cpu);
419 /* This actually kills the CPU. */
422 /* CPU is completely dead: tell everyone. Too late to complain. */
423 tick_cleanup_dead_cpu(cpu);
424 cpu_notify_nofail(CPU_DEAD | mod, hcpu);
426 check_for_tasks(cpu);
430 trace_sched_cpu_hotplug(cpu, err, 0);
432 cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
436 int cpu_down(unsigned int cpu)
440 cpu_maps_update_begin();
442 if (cpu_hotplug_disabled) {
447 err = _cpu_down(cpu, 0);
450 cpu_maps_update_done();
453 EXPORT_SYMBOL(cpu_down);
454 #endif /*CONFIG_HOTPLUG_CPU*/
457 * Unpark per-CPU smpboot kthreads at CPU-online time.
459 static int smpboot_thread_call(struct notifier_block *nfb,
460 unsigned long action, void *hcpu)
462 int cpu = (long)hcpu;
464 switch (action & ~CPU_TASKS_FROZEN) {
466 case CPU_DOWN_FAILED:
468 smpboot_unpark_threads(cpu);
478 static struct notifier_block smpboot_thread_notifier = {
479 .notifier_call = smpboot_thread_call,
480 .priority = CPU_PRI_SMPBOOT,
483 void smpboot_thread_init(void)
485 register_cpu_notifier(&smpboot_thread_notifier);
488 /* Requires cpu_add_remove_lock to be held */
489 static int _cpu_up(unsigned int cpu, int tasks_frozen)
491 int ret, nr_calls = 0;
492 void *hcpu = (void *)(long)cpu;
493 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
494 struct task_struct *idle;
498 if (cpu_online(cpu) || !cpu_present(cpu)) {
503 idle = idle_thread_get(cpu);
509 ret = smpboot_create_threads(cpu);
513 ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
516 pr_warn("%s: attempt to bring up CPU %u failed\n",
521 /* Arch-specific enabling code. */
522 ret = __cpu_up(cpu, idle);
526 BUG_ON(!cpu_online(cpu));
528 /* Now call notifier in preparation. */
529 cpu_notify(CPU_ONLINE | mod, hcpu);
533 __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
536 trace_sched_cpu_hotplug(cpu, ret, 1);
541 int cpu_up(unsigned int cpu)
545 if (!cpu_possible(cpu)) {
546 pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n",
548 #if defined(CONFIG_IA64)
549 pr_err("please check additional_cpus= boot parameter\n");
554 err = try_online_node(cpu_to_node(cpu));
558 cpu_maps_update_begin();
560 if (cpu_hotplug_disabled) {
565 err = _cpu_up(cpu, 0);
568 cpu_maps_update_done();
571 EXPORT_SYMBOL_GPL(cpu_up);
573 #ifdef CONFIG_PM_SLEEP_SMP
574 static cpumask_var_t frozen_cpus;
576 int disable_nonboot_cpus(void)
578 int cpu, first_cpu, error = 0;
580 cpu_maps_update_begin();
581 first_cpu = cpumask_first(cpu_online_mask);
583 * We take down all of the non-boot CPUs in one shot to avoid races
584 * with the userspace trying to use the CPU hotplug at the same time
586 cpumask_clear(frozen_cpus);
588 pr_info("Disabling non-boot CPUs ...\n");
589 for_each_online_cpu(cpu) {
590 if (cpu == first_cpu)
592 trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
593 error = _cpu_down(cpu, 1);
594 trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
596 cpumask_set_cpu(cpu, frozen_cpus);
598 pr_err("Error taking CPU%d down: %d\n", cpu, error);
604 BUG_ON(num_online_cpus() > 1);
606 pr_err("Non-boot CPUs are not disabled\n");
609 * Make sure the CPUs won't be enabled by someone else. We need to do
610 * this even in case of failure as all disable_nonboot_cpus() users are
611 * supposed to do enable_nonboot_cpus() on the failure path.
613 cpu_hotplug_disabled++;
615 cpu_maps_update_done();
619 void __weak arch_enable_nonboot_cpus_begin(void)
623 void __weak arch_enable_nonboot_cpus_end(void)
627 void enable_nonboot_cpus(void)
631 /* Allow everyone to use the CPU hotplug again */
632 cpu_maps_update_begin();
633 WARN_ON(--cpu_hotplug_disabled < 0);
634 if (cpumask_empty(frozen_cpus))
637 pr_info("Enabling non-boot CPUs ...\n");
639 arch_enable_nonboot_cpus_begin();
641 for_each_cpu(cpu, frozen_cpus) {
642 trace_suspend_resume(TPS("CPU_ON"), cpu, true);
643 error = _cpu_up(cpu, 1);
644 trace_suspend_resume(TPS("CPU_ON"), cpu, false);
646 pr_info("CPU%d is up\n", cpu);
649 pr_warn("Error taking CPU%d up: %d\n", cpu, error);
652 arch_enable_nonboot_cpus_end();
654 cpumask_clear(frozen_cpus);
656 cpu_maps_update_done();
659 static int __init alloc_frozen_cpus(void)
661 if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
665 core_initcall(alloc_frozen_cpus);
668 * When callbacks for CPU hotplug notifications are being executed, we must
669 * ensure that the state of the system with respect to the tasks being frozen
670 * or not, as reported by the notification, remains unchanged *throughout the
671 * duration* of the execution of the callbacks.
672 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
674 * This synchronization is implemented by mutually excluding regular CPU
675 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
676 * Hibernate notifications.
679 cpu_hotplug_pm_callback(struct notifier_block *nb,
680 unsigned long action, void *ptr)
684 case PM_SUSPEND_PREPARE:
685 case PM_HIBERNATION_PREPARE:
686 cpu_hotplug_disable();
689 case PM_POST_SUSPEND:
690 case PM_POST_HIBERNATION:
691 cpu_hotplug_enable();
702 static int __init cpu_hotplug_pm_sync_init(void)
705 * cpu_hotplug_pm_callback has higher priority than x86
706 * bsp_pm_callback which depends on cpu_hotplug_pm_callback
707 * to disable cpu hotplug to avoid cpu hotplug race.
709 pm_notifier(cpu_hotplug_pm_callback, 0);
712 core_initcall(cpu_hotplug_pm_sync_init);
714 #endif /* CONFIG_PM_SLEEP_SMP */
717 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
718 * @cpu: cpu that just started
720 * This function calls the cpu_chain notifiers with CPU_STARTING.
721 * It must be called by the arch code on the new cpu, before the new cpu
722 * enables interrupts and before the "boot" cpu returns from __cpu_up().
724 void notify_cpu_starting(unsigned int cpu)
726 unsigned long val = CPU_STARTING;
728 #ifdef CONFIG_PM_SLEEP_SMP
729 if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
730 val = CPU_STARTING_FROZEN;
731 #endif /* CONFIG_PM_SLEEP_SMP */
732 cpu_notify(val, (void *)(long)cpu);
735 #endif /* CONFIG_SMP */
738 * cpu_bit_bitmap[] is a special, "compressed" data structure that
739 * represents all NR_CPUS bits binary values of 1<<nr.
741 * It is used by cpumask_of() to get a constant address to a CPU
742 * mask value that has a single bit set only.
745 /* cpu_bit_bitmap[0] is empty - so we can back into it */
746 #define MASK_DECLARE_1(x) [x+1][0] = (1UL << (x))
747 #define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
748 #define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
749 #define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
751 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
753 MASK_DECLARE_8(0), MASK_DECLARE_8(8),
754 MASK_DECLARE_8(16), MASK_DECLARE_8(24),
755 #if BITS_PER_LONG > 32
756 MASK_DECLARE_8(32), MASK_DECLARE_8(40),
757 MASK_DECLARE_8(48), MASK_DECLARE_8(56),
760 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
762 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
763 EXPORT_SYMBOL(cpu_all_bits);
765 #ifdef CONFIG_INIT_ALL_POSSIBLE
766 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
769 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
771 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
772 EXPORT_SYMBOL(cpu_possible_mask);
774 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
775 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
776 EXPORT_SYMBOL(cpu_online_mask);
778 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
779 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
780 EXPORT_SYMBOL(cpu_present_mask);
782 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
783 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
784 EXPORT_SYMBOL(cpu_active_mask);
786 void set_cpu_possible(unsigned int cpu, bool possible)
789 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
791 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
794 void set_cpu_present(unsigned int cpu, bool present)
797 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
799 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
802 void set_cpu_online(unsigned int cpu, bool online)
805 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
806 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
808 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
812 void set_cpu_active(unsigned int cpu, bool active)
815 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
817 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
820 void init_cpu_present(const struct cpumask *src)
822 cpumask_copy(to_cpumask(cpu_present_bits), src);
825 void init_cpu_possible(const struct cpumask *src)
827 cpumask_copy(to_cpumask(cpu_possible_bits), src);
830 void init_cpu_online(const struct cpumask *src)
832 cpumask_copy(to_cpumask(cpu_online_bits), src);
835 static ATOMIC_NOTIFIER_HEAD(idle_notifier);
837 void idle_notifier_register(struct notifier_block *n)
839 atomic_notifier_chain_register(&idle_notifier, n);
841 EXPORT_SYMBOL_GPL(idle_notifier_register);
843 void idle_notifier_unregister(struct notifier_block *n)
845 atomic_notifier_chain_unregister(&idle_notifier, n);
847 EXPORT_SYMBOL_GPL(idle_notifier_unregister);
849 void idle_notifier_call_chain(unsigned long val)
851 atomic_notifier_call_chain(&idle_notifier, val, NULL);
853 EXPORT_SYMBOL_GPL(idle_notifier_call_chain);