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>
27 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
28 static DEFINE_MUTEX(cpu_add_remove_lock);
31 * The following two API's must be used when attempting
32 * to serialize the updates to cpu_online_mask, cpu_present_mask.
34 void cpu_maps_update_begin(void)
36 mutex_lock(&cpu_add_remove_lock);
39 void cpu_maps_update_done(void)
41 mutex_unlock(&cpu_add_remove_lock);
44 static RAW_NOTIFIER_HEAD(cpu_chain);
46 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
47 * Should always be manipulated under cpu_add_remove_lock
49 static int cpu_hotplug_disabled;
51 #ifdef CONFIG_HOTPLUG_CPU
54 struct task_struct *active_writer;
55 struct mutex lock; /* Synchronizes accesses to refcount, */
57 * Also blocks the new readers during
58 * an ongoing cpu hotplug operation.
62 #ifdef CONFIG_DEBUG_LOCK_ALLOC
63 struct lockdep_map dep_map;
66 .active_writer = NULL,
67 .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
69 #ifdef CONFIG_DEBUG_LOCK_ALLOC
70 .dep_map = {.name = "cpu_hotplug.lock" },
74 /* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
75 #define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
76 #define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map)
77 #define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map)
79 void get_online_cpus(void)
82 if (cpu_hotplug.active_writer == current)
84 cpuhp_lock_acquire_read();
85 mutex_lock(&cpu_hotplug.lock);
86 cpu_hotplug.refcount++;
87 mutex_unlock(&cpu_hotplug.lock);
90 EXPORT_SYMBOL_GPL(get_online_cpus);
92 void put_online_cpus(void)
94 if (cpu_hotplug.active_writer == current)
96 mutex_lock(&cpu_hotplug.lock);
98 if (WARN_ON(!cpu_hotplug.refcount))
99 cpu_hotplug.refcount++; /* try to fix things up */
101 if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
102 wake_up_process(cpu_hotplug.active_writer);
103 mutex_unlock(&cpu_hotplug.lock);
104 cpuhp_lock_release();
107 EXPORT_SYMBOL_GPL(put_online_cpus);
110 * This ensures that the hotplug operation can begin only when the
111 * refcount goes to zero.
113 * Note that during a cpu-hotplug operation, the new readers, if any,
114 * will be blocked by the cpu_hotplug.lock
116 * Since cpu_hotplug_begin() is always called after invoking
117 * cpu_maps_update_begin(), we can be sure that only one writer is active.
119 * Note that theoretically, there is a possibility of a livelock:
120 * - Refcount goes to zero, last reader wakes up the sleeping
122 * - Last reader unlocks the cpu_hotplug.lock.
123 * - A new reader arrives at this moment, bumps up the refcount.
124 * - The writer acquires the cpu_hotplug.lock finds the refcount
125 * non zero and goes to sleep again.
127 * However, this is very difficult to achieve in practice since
128 * get_online_cpus() not an api which is called all that often.
131 void cpu_hotplug_begin(void)
133 cpu_hotplug.active_writer = current;
135 cpuhp_lock_acquire();
137 mutex_lock(&cpu_hotplug.lock);
138 if (likely(!cpu_hotplug.refcount))
140 __set_current_state(TASK_UNINTERRUPTIBLE);
141 mutex_unlock(&cpu_hotplug.lock);
146 void cpu_hotplug_done(void)
148 cpu_hotplug.active_writer = NULL;
149 mutex_unlock(&cpu_hotplug.lock);
150 cpuhp_lock_release();
154 * Wait for currently running CPU hotplug operations to complete (if any) and
155 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
156 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
157 * hotplug path before performing hotplug operations. So acquiring that lock
158 * guarantees mutual exclusion from any currently running hotplug operations.
160 void cpu_hotplug_disable(void)
162 cpu_maps_update_begin();
163 cpu_hotplug_disabled = 1;
164 cpu_maps_update_done();
167 void cpu_hotplug_enable(void)
169 cpu_maps_update_begin();
170 cpu_hotplug_disabled = 0;
171 cpu_maps_update_done();
174 #endif /* CONFIG_HOTPLUG_CPU */
176 /* Need to know about CPUs going up/down? */
177 int __ref register_cpu_notifier(struct notifier_block *nb)
180 cpu_maps_update_begin();
181 ret = raw_notifier_chain_register(&cpu_chain, nb);
182 cpu_maps_update_done();
186 static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
191 ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
194 return notifier_to_errno(ret);
197 static int cpu_notify(unsigned long val, void *v)
199 return __cpu_notify(val, v, -1, NULL);
202 #ifdef CONFIG_HOTPLUG_CPU
204 static void cpu_notify_nofail(unsigned long val, void *v)
206 BUG_ON(cpu_notify(val, v));
208 EXPORT_SYMBOL(register_cpu_notifier);
210 void __ref unregister_cpu_notifier(struct notifier_block *nb)
212 cpu_maps_update_begin();
213 raw_notifier_chain_unregister(&cpu_chain, nb);
214 cpu_maps_update_done();
216 EXPORT_SYMBOL(unregister_cpu_notifier);
219 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
222 * This function walks all processes, finds a valid mm struct for each one and
223 * then clears a corresponding bit in mm's cpumask. While this all sounds
224 * trivial, there are various non-obvious corner cases, which this function
225 * tries to solve in a safe manner.
227 * Also note that the function uses a somewhat relaxed locking scheme, so it may
228 * be called only for an already offlined CPU.
230 void clear_tasks_mm_cpumask(int cpu)
232 struct task_struct *p;
235 * This function is called after the cpu is taken down and marked
236 * offline, so its not like new tasks will ever get this cpu set in
237 * their mm mask. -- Peter Zijlstra
238 * Thus, we may use rcu_read_lock() here, instead of grabbing
239 * full-fledged tasklist_lock.
241 WARN_ON(cpu_online(cpu));
243 for_each_process(p) {
244 struct task_struct *t;
247 * Main thread might exit, but other threads may still have
248 * a valid mm. Find one.
250 t = find_lock_task_mm(p);
253 cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
259 static inline void check_for_tasks(int cpu)
261 struct task_struct *p;
262 cputime_t utime, stime;
264 write_lock_irq(&tasklist_lock);
265 for_each_process(p) {
266 task_cputime(p, &utime, &stime);
267 if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
269 printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
270 "(state = %ld, flags = %x)\n",
271 p->comm, task_pid_nr(p), cpu,
274 write_unlock_irq(&tasklist_lock);
277 struct take_cpu_down_param {
282 /* Take this CPU down. */
283 static int __ref take_cpu_down(void *_param)
285 struct take_cpu_down_param *param = _param;
288 /* Ensure this CPU doesn't handle any more interrupts. */
289 err = __cpu_disable();
293 cpu_notify(CPU_DYING | param->mod, param->hcpu);
294 /* Park the stopper thread */
295 kthread_park(current);
299 /* Requires cpu_add_remove_lock to be held */
300 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
302 int err, nr_calls = 0;
303 void *hcpu = (void *)(long)cpu;
304 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
305 struct take_cpu_down_param tcd_param = {
310 if (num_online_cpus() == 1)
313 if (!cpu_online(cpu))
318 err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
321 __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
322 printk("%s: attempt to take down CPU %u failed\n",
328 * By now we've cleared cpu_active_mask, wait for all preempt-disabled
329 * and RCU users of this state to go away such that all new such users
332 * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
333 * not imply sync_sched(), so explicitly call both.
335 * Do sync before park smpboot threads to take care the rcu boost case.
337 #ifdef CONFIG_PREEMPT
342 smpboot_park_threads(cpu);
345 * So now all preempt/rcu users must observe !cpu_active().
348 err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
350 /* CPU didn't die: tell everyone. Can't complain. */
351 smpboot_unpark_threads(cpu);
352 cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
355 BUG_ON(cpu_online(cpu));
358 * The migration_call() CPU_DYING callback will have removed all
359 * runnable tasks from the cpu, there's only the idle task left now
360 * that the migration thread is done doing the stop_machine thing.
362 * Wait for the stop thread to go away.
364 while (!idle_cpu(cpu))
367 /* This actually kills the CPU. */
370 /* CPU is completely dead: tell everyone. Too late to complain. */
371 cpu_notify_nofail(CPU_DEAD | mod, hcpu);
373 check_for_tasks(cpu);
378 cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
382 int __ref cpu_down(unsigned int cpu)
386 cpu_maps_update_begin();
388 if (cpu_hotplug_disabled) {
393 err = _cpu_down(cpu, 0);
396 cpu_maps_update_done();
399 EXPORT_SYMBOL(cpu_down);
400 #endif /*CONFIG_HOTPLUG_CPU*/
402 /* Requires cpu_add_remove_lock to be held */
403 static int _cpu_up(unsigned int cpu, int tasks_frozen)
405 int ret, nr_calls = 0;
406 void *hcpu = (void *)(long)cpu;
407 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
408 struct task_struct *idle;
412 if (cpu_online(cpu) || !cpu_present(cpu)) {
417 idle = idle_thread_get(cpu);
423 ret = smpboot_create_threads(cpu);
427 ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
430 printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
435 /* Arch-specific enabling code. */
436 ret = __cpu_up(cpu, idle);
439 BUG_ON(!cpu_online(cpu));
441 /* Wake the per cpu threads */
442 smpboot_unpark_threads(cpu);
444 /* Now call notifier in preparation. */
445 cpu_notify(CPU_ONLINE | mod, hcpu);
449 __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
456 int cpu_up(unsigned int cpu)
460 if (!cpu_possible(cpu)) {
461 printk(KERN_ERR "can't online cpu %d because it is not "
462 "configured as may-hotadd at boot time\n", cpu);
463 #if defined(CONFIG_IA64)
464 printk(KERN_ERR "please check additional_cpus= boot "
470 err = try_online_node(cpu_to_node(cpu));
474 cpu_maps_update_begin();
476 if (cpu_hotplug_disabled) {
481 err = _cpu_up(cpu, 0);
484 cpu_maps_update_done();
487 EXPORT_SYMBOL_GPL(cpu_up);
489 #ifdef CONFIG_PM_SLEEP_SMP
490 static cpumask_var_t frozen_cpus;
492 int disable_nonboot_cpus(void)
494 int cpu, first_cpu, error = 0;
496 cpu_maps_update_begin();
497 first_cpu = cpumask_first(cpu_online_mask);
499 * We take down all of the non-boot CPUs in one shot to avoid races
500 * with the userspace trying to use the CPU hotplug at the same time
502 cpumask_clear(frozen_cpus);
504 printk("Disabling non-boot CPUs ...\n");
505 for_each_online_cpu(cpu) {
506 if (cpu == first_cpu)
508 error = _cpu_down(cpu, 1);
510 cpumask_set_cpu(cpu, frozen_cpus);
512 printk(KERN_ERR "Error taking CPU%d down: %d\n",
519 BUG_ON(num_online_cpus() > 1);
520 /* Make sure the CPUs won't be enabled by someone else */
521 cpu_hotplug_disabled = 1;
523 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
525 cpu_maps_update_done();
529 void __weak arch_enable_nonboot_cpus_begin(void)
533 void __weak arch_enable_nonboot_cpus_end(void)
537 void __ref enable_nonboot_cpus(void)
541 /* Allow everyone to use the CPU hotplug again */
542 cpu_maps_update_begin();
543 cpu_hotplug_disabled = 0;
544 if (cpumask_empty(frozen_cpus))
547 printk(KERN_INFO "Enabling non-boot CPUs ...\n");
549 arch_enable_nonboot_cpus_begin();
551 for_each_cpu(cpu, frozen_cpus) {
552 error = _cpu_up(cpu, 1);
554 printk(KERN_INFO "CPU%d is up\n", cpu);
557 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
560 arch_enable_nonboot_cpus_end();
562 cpumask_clear(frozen_cpus);
564 cpu_maps_update_done();
567 static int __init alloc_frozen_cpus(void)
569 if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
573 core_initcall(alloc_frozen_cpus);
576 * When callbacks for CPU hotplug notifications are being executed, we must
577 * ensure that the state of the system with respect to the tasks being frozen
578 * or not, as reported by the notification, remains unchanged *throughout the
579 * duration* of the execution of the callbacks.
580 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
582 * This synchronization is implemented by mutually excluding regular CPU
583 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
584 * Hibernate notifications.
587 cpu_hotplug_pm_callback(struct notifier_block *nb,
588 unsigned long action, void *ptr)
592 case PM_SUSPEND_PREPARE:
593 case PM_HIBERNATION_PREPARE:
594 cpu_hotplug_disable();
597 case PM_POST_SUSPEND:
598 case PM_POST_HIBERNATION:
599 cpu_hotplug_enable();
610 static int __init cpu_hotplug_pm_sync_init(void)
613 * cpu_hotplug_pm_callback has higher priority than x86
614 * bsp_pm_callback which depends on cpu_hotplug_pm_callback
615 * to disable cpu hotplug to avoid cpu hotplug race.
617 pm_notifier(cpu_hotplug_pm_callback, 0);
620 core_initcall(cpu_hotplug_pm_sync_init);
622 #endif /* CONFIG_PM_SLEEP_SMP */
625 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
626 * @cpu: cpu that just started
628 * This function calls the cpu_chain notifiers with CPU_STARTING.
629 * It must be called by the arch code on the new cpu, before the new cpu
630 * enables interrupts and before the "boot" cpu returns from __cpu_up().
632 void notify_cpu_starting(unsigned int cpu)
634 unsigned long val = CPU_STARTING;
636 #ifdef CONFIG_PM_SLEEP_SMP
637 if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
638 val = CPU_STARTING_FROZEN;
639 #endif /* CONFIG_PM_SLEEP_SMP */
640 cpu_notify(val, (void *)(long)cpu);
643 #endif /* CONFIG_SMP */
646 * cpu_bit_bitmap[] is a special, "compressed" data structure that
647 * represents all NR_CPUS bits binary values of 1<<nr.
649 * It is used by cpumask_of() to get a constant address to a CPU
650 * mask value that has a single bit set only.
653 /* cpu_bit_bitmap[0] is empty - so we can back into it */
654 #define MASK_DECLARE_1(x) [x+1][0] = (1UL << (x))
655 #define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
656 #define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
657 #define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
659 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
661 MASK_DECLARE_8(0), MASK_DECLARE_8(8),
662 MASK_DECLARE_8(16), MASK_DECLARE_8(24),
663 #if BITS_PER_LONG > 32
664 MASK_DECLARE_8(32), MASK_DECLARE_8(40),
665 MASK_DECLARE_8(48), MASK_DECLARE_8(56),
668 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
670 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
671 EXPORT_SYMBOL(cpu_all_bits);
673 #ifdef CONFIG_INIT_ALL_POSSIBLE
674 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
677 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
679 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
680 EXPORT_SYMBOL(cpu_possible_mask);
682 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
683 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
684 EXPORT_SYMBOL(cpu_online_mask);
686 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
687 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
688 EXPORT_SYMBOL(cpu_present_mask);
690 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
691 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
692 EXPORT_SYMBOL(cpu_active_mask);
694 void set_cpu_possible(unsigned int cpu, bool possible)
697 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
699 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
702 void set_cpu_present(unsigned int cpu, bool present)
705 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
707 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
710 void set_cpu_online(unsigned int cpu, bool online)
713 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
715 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
718 void set_cpu_active(unsigned int cpu, bool active)
721 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
723 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
726 void init_cpu_present(const struct cpumask *src)
728 cpumask_copy(to_cpumask(cpu_present_bits), src);
731 void init_cpu_possible(const struct cpumask *src)
733 cpumask_copy(to_cpumask(cpu_possible_bits), src);
736 void init_cpu_online(const struct cpumask *src)
738 cpumask_copy(to_cpumask(cpu_online_bits), src);