xref: /openbmc/linux/kernel/smp.c (revision c819e2cf)
1 /*
2  * Generic helpers for smp ipi calls
3  *
4  * (C) Jens Axboe <jens.axboe@oracle.com> 2008
5  */
6 #include <linux/irq_work.h>
7 #include <linux/rcupdate.h>
8 #include <linux/rculist.h>
9 #include <linux/kernel.h>
10 #include <linux/export.h>
11 #include <linux/percpu.h>
12 #include <linux/init.h>
13 #include <linux/gfp.h>
14 #include <linux/smp.h>
15 #include <linux/cpu.h>
16 #include <linux/sched.h>
17 
18 #include "smpboot.h"
19 
20 enum {
21 	CSD_FLAG_LOCK		= 0x01,
22 	CSD_FLAG_WAIT		= 0x02,
23 };
24 
25 struct call_function_data {
26 	struct call_single_data	__percpu *csd;
27 	cpumask_var_t		cpumask;
28 };
29 
30 static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
31 
32 static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);
33 
34 static void flush_smp_call_function_queue(bool warn_cpu_offline);
35 
36 static int
37 hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
38 {
39 	long cpu = (long)hcpu;
40 	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
41 
42 	switch (action) {
43 	case CPU_UP_PREPARE:
44 	case CPU_UP_PREPARE_FROZEN:
45 		if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
46 				cpu_to_node(cpu)))
47 			return notifier_from_errno(-ENOMEM);
48 		cfd->csd = alloc_percpu(struct call_single_data);
49 		if (!cfd->csd) {
50 			free_cpumask_var(cfd->cpumask);
51 			return notifier_from_errno(-ENOMEM);
52 		}
53 		break;
54 
55 #ifdef CONFIG_HOTPLUG_CPU
56 	case CPU_UP_CANCELED:
57 	case CPU_UP_CANCELED_FROZEN:
58 		/* Fall-through to the CPU_DEAD[_FROZEN] case. */
59 
60 	case CPU_DEAD:
61 	case CPU_DEAD_FROZEN:
62 		free_cpumask_var(cfd->cpumask);
63 		free_percpu(cfd->csd);
64 		break;
65 
66 	case CPU_DYING:
67 	case CPU_DYING_FROZEN:
68 		/*
69 		 * The IPIs for the smp-call-function callbacks queued by other
70 		 * CPUs might arrive late, either due to hardware latencies or
71 		 * because this CPU disabled interrupts (inside stop-machine)
72 		 * before the IPIs were sent. So flush out any pending callbacks
73 		 * explicitly (without waiting for the IPIs to arrive), to
74 		 * ensure that the outgoing CPU doesn't go offline with work
75 		 * still pending.
76 		 */
77 		flush_smp_call_function_queue(false);
78 		break;
79 #endif
80 	};
81 
82 	return NOTIFY_OK;
83 }
84 
85 static struct notifier_block hotplug_cfd_notifier = {
86 	.notifier_call		= hotplug_cfd,
87 };
88 
89 void __init call_function_init(void)
90 {
91 	void *cpu = (void *)(long)smp_processor_id();
92 	int i;
93 
94 	for_each_possible_cpu(i)
95 		init_llist_head(&per_cpu(call_single_queue, i));
96 
97 	hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
98 	register_cpu_notifier(&hotplug_cfd_notifier);
99 }
100 
101 /*
102  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
103  *
104  * For non-synchronous ipi calls the csd can still be in use by the
105  * previous function call. For multi-cpu calls its even more interesting
106  * as we'll have to ensure no other cpu is observing our csd.
107  */
108 static void csd_lock_wait(struct call_single_data *csd)
109 {
110 	while (csd->flags & CSD_FLAG_LOCK)
111 		cpu_relax();
112 }
113 
114 static void csd_lock(struct call_single_data *csd)
115 {
116 	csd_lock_wait(csd);
117 	csd->flags |= CSD_FLAG_LOCK;
118 
119 	/*
120 	 * prevent CPU from reordering the above assignment
121 	 * to ->flags with any subsequent assignments to other
122 	 * fields of the specified call_single_data structure:
123 	 */
124 	smp_mb();
125 }
126 
127 static void csd_unlock(struct call_single_data *csd)
128 {
129 	WARN_ON((csd->flags & CSD_FLAG_WAIT) && !(csd->flags & CSD_FLAG_LOCK));
130 
131 	/*
132 	 * ensure we're all done before releasing data:
133 	 */
134 	smp_mb();
135 
136 	csd->flags &= ~CSD_FLAG_LOCK;
137 }
138 
139 static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
140 
141 /*
142  * Insert a previously allocated call_single_data element
143  * for execution on the given CPU. data must already have
144  * ->func, ->info, and ->flags set.
145  */
146 static int generic_exec_single(int cpu, struct call_single_data *csd,
147 			       smp_call_func_t func, void *info, int wait)
148 {
149 	struct call_single_data csd_stack = { .flags = 0 };
150 	unsigned long flags;
151 
152 
153 	if (cpu == smp_processor_id()) {
154 		local_irq_save(flags);
155 		func(info);
156 		local_irq_restore(flags);
157 		return 0;
158 	}
159 
160 
161 	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu))
162 		return -ENXIO;
163 
164 
165 	if (!csd) {
166 		csd = &csd_stack;
167 		if (!wait)
168 			csd = this_cpu_ptr(&csd_data);
169 	}
170 
171 	csd_lock(csd);
172 
173 	csd->func = func;
174 	csd->info = info;
175 
176 	if (wait)
177 		csd->flags |= CSD_FLAG_WAIT;
178 
179 	/*
180 	 * The list addition should be visible before sending the IPI
181 	 * handler locks the list to pull the entry off it because of
182 	 * normal cache coherency rules implied by spinlocks.
183 	 *
184 	 * If IPIs can go out of order to the cache coherency protocol
185 	 * in an architecture, sufficient synchronisation should be added
186 	 * to arch code to make it appear to obey cache coherency WRT
187 	 * locking and barrier primitives. Generic code isn't really
188 	 * equipped to do the right thing...
189 	 */
190 	if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
191 		arch_send_call_function_single_ipi(cpu);
192 
193 	if (wait)
194 		csd_lock_wait(csd);
195 
196 	return 0;
197 }
198 
199 /**
200  * generic_smp_call_function_single_interrupt - Execute SMP IPI callbacks
201  *
202  * Invoked by arch to handle an IPI for call function single.
203  * Must be called with interrupts disabled.
204  */
205 void generic_smp_call_function_single_interrupt(void)
206 {
207 	flush_smp_call_function_queue(true);
208 }
209 
210 /**
211  * flush_smp_call_function_queue - Flush pending smp-call-function callbacks
212  *
213  * @warn_cpu_offline: If set to 'true', warn if callbacks were queued on an
214  *		      offline CPU. Skip this check if set to 'false'.
215  *
216  * Flush any pending smp-call-function callbacks queued on this CPU. This is
217  * invoked by the generic IPI handler, as well as by a CPU about to go offline,
218  * to ensure that all pending IPI callbacks are run before it goes completely
219  * offline.
220  *
221  * Loop through the call_single_queue and run all the queued callbacks.
222  * Must be called with interrupts disabled.
223  */
224 static void flush_smp_call_function_queue(bool warn_cpu_offline)
225 {
226 	struct llist_head *head;
227 	struct llist_node *entry;
228 	struct call_single_data *csd, *csd_next;
229 	static bool warned;
230 
231 	WARN_ON(!irqs_disabled());
232 
233 	head = this_cpu_ptr(&call_single_queue);
234 	entry = llist_del_all(head);
235 	entry = llist_reverse_order(entry);
236 
237 	/* There shouldn't be any pending callbacks on an offline CPU. */
238 	if (unlikely(warn_cpu_offline && !cpu_online(smp_processor_id()) &&
239 		     !warned && !llist_empty(head))) {
240 		warned = true;
241 		WARN(1, "IPI on offline CPU %d\n", smp_processor_id());
242 
243 		/*
244 		 * We don't have to use the _safe() variant here
245 		 * because we are not invoking the IPI handlers yet.
246 		 */
247 		llist_for_each_entry(csd, entry, llist)
248 			pr_warn("IPI callback %pS sent to offline CPU\n",
249 				csd->func);
250 	}
251 
252 	llist_for_each_entry_safe(csd, csd_next, entry, llist) {
253 		csd->func(csd->info);
254 		csd_unlock(csd);
255 	}
256 
257 	/*
258 	 * Handle irq works queued remotely by irq_work_queue_on().
259 	 * Smp functions above are typically synchronous so they
260 	 * better run first since some other CPUs may be busy waiting
261 	 * for them.
262 	 */
263 	irq_work_run();
264 }
265 
266 /*
267  * smp_call_function_single - Run a function on a specific CPU
268  * @func: The function to run. This must be fast and non-blocking.
269  * @info: An arbitrary pointer to pass to the function.
270  * @wait: If true, wait until function has completed on other CPUs.
271  *
272  * Returns 0 on success, else a negative status code.
273  */
274 int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
275 			     int wait)
276 {
277 	int this_cpu;
278 	int err;
279 
280 	/*
281 	 * prevent preemption and reschedule on another processor,
282 	 * as well as CPU removal
283 	 */
284 	this_cpu = get_cpu();
285 
286 	/*
287 	 * Can deadlock when called with interrupts disabled.
288 	 * We allow cpu's that are not yet online though, as no one else can
289 	 * send smp call function interrupt to this cpu and as such deadlocks
290 	 * can't happen.
291 	 */
292 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
293 		     && !oops_in_progress);
294 
295 	err = generic_exec_single(cpu, NULL, func, info, wait);
296 
297 	put_cpu();
298 
299 	return err;
300 }
301 EXPORT_SYMBOL(smp_call_function_single);
302 
303 /**
304  * smp_call_function_single_async(): Run an asynchronous function on a
305  * 			         specific CPU.
306  * @cpu: The CPU to run on.
307  * @csd: Pre-allocated and setup data structure
308  *
309  * Like smp_call_function_single(), but the call is asynchonous and
310  * can thus be done from contexts with disabled interrupts.
311  *
312  * The caller passes his own pre-allocated data structure
313  * (ie: embedded in an object) and is responsible for synchronizing it
314  * such that the IPIs performed on the @csd are strictly serialized.
315  *
316  * NOTE: Be careful, there is unfortunately no current debugging facility to
317  * validate the correctness of this serialization.
318  */
319 int smp_call_function_single_async(int cpu, struct call_single_data *csd)
320 {
321 	int err = 0;
322 
323 	preempt_disable();
324 	err = generic_exec_single(cpu, csd, csd->func, csd->info, 0);
325 	preempt_enable();
326 
327 	return err;
328 }
329 EXPORT_SYMBOL_GPL(smp_call_function_single_async);
330 
331 /*
332  * smp_call_function_any - Run a function on any of the given cpus
333  * @mask: The mask of cpus it can run on.
334  * @func: The function to run. This must be fast and non-blocking.
335  * @info: An arbitrary pointer to pass to the function.
336  * @wait: If true, wait until function has completed.
337  *
338  * Returns 0 on success, else a negative status code (if no cpus were online).
339  *
340  * Selection preference:
341  *	1) current cpu if in @mask
342  *	2) any cpu of current node if in @mask
343  *	3) any other online cpu in @mask
344  */
345 int smp_call_function_any(const struct cpumask *mask,
346 			  smp_call_func_t func, void *info, int wait)
347 {
348 	unsigned int cpu;
349 	const struct cpumask *nodemask;
350 	int ret;
351 
352 	/* Try for same CPU (cheapest) */
353 	cpu = get_cpu();
354 	if (cpumask_test_cpu(cpu, mask))
355 		goto call;
356 
357 	/* Try for same node. */
358 	nodemask = cpumask_of_node(cpu_to_node(cpu));
359 	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
360 	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
361 		if (cpu_online(cpu))
362 			goto call;
363 	}
364 
365 	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
366 	cpu = cpumask_any_and(mask, cpu_online_mask);
367 call:
368 	ret = smp_call_function_single(cpu, func, info, wait);
369 	put_cpu();
370 	return ret;
371 }
372 EXPORT_SYMBOL_GPL(smp_call_function_any);
373 
374 /**
375  * smp_call_function_many(): Run a function on a set of other CPUs.
376  * @mask: The set of cpus to run on (only runs on online subset).
377  * @func: The function to run. This must be fast and non-blocking.
378  * @info: An arbitrary pointer to pass to the function.
379  * @wait: If true, wait (atomically) until function has completed
380  *        on other CPUs.
381  *
382  * If @wait is true, then returns once @func has returned.
383  *
384  * You must not call this function with disabled interrupts or from a
385  * hardware interrupt handler or from a bottom half handler. Preemption
386  * must be disabled when calling this function.
387  */
388 void smp_call_function_many(const struct cpumask *mask,
389 			    smp_call_func_t func, void *info, bool wait)
390 {
391 	struct call_function_data *cfd;
392 	int cpu, next_cpu, this_cpu = smp_processor_id();
393 
394 	/*
395 	 * Can deadlock when called with interrupts disabled.
396 	 * We allow cpu's that are not yet online though, as no one else can
397 	 * send smp call function interrupt to this cpu and as such deadlocks
398 	 * can't happen.
399 	 */
400 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
401 		     && !oops_in_progress && !early_boot_irqs_disabled);
402 
403 	/* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */
404 	cpu = cpumask_first_and(mask, cpu_online_mask);
405 	if (cpu == this_cpu)
406 		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
407 
408 	/* No online cpus?  We're done. */
409 	if (cpu >= nr_cpu_ids)
410 		return;
411 
412 	/* Do we have another CPU which isn't us? */
413 	next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
414 	if (next_cpu == this_cpu)
415 		next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
416 
417 	/* Fastpath: do that cpu by itself. */
418 	if (next_cpu >= nr_cpu_ids) {
419 		smp_call_function_single(cpu, func, info, wait);
420 		return;
421 	}
422 
423 	cfd = this_cpu_ptr(&cfd_data);
424 
425 	cpumask_and(cfd->cpumask, mask, cpu_online_mask);
426 	cpumask_clear_cpu(this_cpu, cfd->cpumask);
427 
428 	/* Some callers race with other cpus changing the passed mask */
429 	if (unlikely(!cpumask_weight(cfd->cpumask)))
430 		return;
431 
432 	for_each_cpu(cpu, cfd->cpumask) {
433 		struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
434 
435 		csd_lock(csd);
436 		csd->func = func;
437 		csd->info = info;
438 		llist_add(&csd->llist, &per_cpu(call_single_queue, cpu));
439 	}
440 
441 	/* Send a message to all CPUs in the map */
442 	arch_send_call_function_ipi_mask(cfd->cpumask);
443 
444 	if (wait) {
445 		for_each_cpu(cpu, cfd->cpumask) {
446 			struct call_single_data *csd;
447 
448 			csd = per_cpu_ptr(cfd->csd, cpu);
449 			csd_lock_wait(csd);
450 		}
451 	}
452 }
453 EXPORT_SYMBOL(smp_call_function_many);
454 
455 /**
456  * smp_call_function(): Run a function on all other CPUs.
457  * @func: The function to run. This must be fast and non-blocking.
458  * @info: An arbitrary pointer to pass to the function.
459  * @wait: If true, wait (atomically) until function has completed
460  *        on other CPUs.
461  *
462  * Returns 0.
463  *
464  * If @wait is true, then returns once @func has returned; otherwise
465  * it returns just before the target cpu calls @func.
466  *
467  * You must not call this function with disabled interrupts or from a
468  * hardware interrupt handler or from a bottom half handler.
469  */
470 int smp_call_function(smp_call_func_t func, void *info, int wait)
471 {
472 	preempt_disable();
473 	smp_call_function_many(cpu_online_mask, func, info, wait);
474 	preempt_enable();
475 
476 	return 0;
477 }
478 EXPORT_SYMBOL(smp_call_function);
479 
480 /* Setup configured maximum number of CPUs to activate */
481 unsigned int setup_max_cpus = NR_CPUS;
482 EXPORT_SYMBOL(setup_max_cpus);
483 
484 
485 /*
486  * Setup routine for controlling SMP activation
487  *
488  * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
489  * activation entirely (the MPS table probe still happens, though).
490  *
491  * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
492  * greater than 0, limits the maximum number of CPUs activated in
493  * SMP mode to <NUM>.
494  */
495 
496 void __weak arch_disable_smp_support(void) { }
497 
498 static int __init nosmp(char *str)
499 {
500 	setup_max_cpus = 0;
501 	arch_disable_smp_support();
502 
503 	return 0;
504 }
505 
506 early_param("nosmp", nosmp);
507 
508 /* this is hard limit */
509 static int __init nrcpus(char *str)
510 {
511 	int nr_cpus;
512 
513 	get_option(&str, &nr_cpus);
514 	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
515 		nr_cpu_ids = nr_cpus;
516 
517 	return 0;
518 }
519 
520 early_param("nr_cpus", nrcpus);
521 
522 static int __init maxcpus(char *str)
523 {
524 	get_option(&str, &setup_max_cpus);
525 	if (setup_max_cpus == 0)
526 		arch_disable_smp_support();
527 
528 	return 0;
529 }
530 
531 early_param("maxcpus", maxcpus);
532 
533 /* Setup number of possible processor ids */
534 int nr_cpu_ids __read_mostly = NR_CPUS;
535 EXPORT_SYMBOL(nr_cpu_ids);
536 
537 /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
538 void __init setup_nr_cpu_ids(void)
539 {
540 	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
541 }
542 
543 void __weak smp_announce(void)
544 {
545 	printk(KERN_INFO "Brought up %d CPUs\n", num_online_cpus());
546 }
547 
548 /* Called by boot processor to activate the rest. */
549 void __init smp_init(void)
550 {
551 	unsigned int cpu;
552 
553 	idle_threads_init();
554 
555 	/* FIXME: This should be done in userspace --RR */
556 	for_each_present_cpu(cpu) {
557 		if (num_online_cpus() >= setup_max_cpus)
558 			break;
559 		if (!cpu_online(cpu))
560 			cpu_up(cpu);
561 	}
562 
563 	/* Any cleanup work */
564 	smp_announce();
565 	smp_cpus_done(setup_max_cpus);
566 }
567 
568 /*
569  * Call a function on all processors.  May be used during early boot while
570  * early_boot_irqs_disabled is set.  Use local_irq_save/restore() instead
571  * of local_irq_disable/enable().
572  */
573 int on_each_cpu(void (*func) (void *info), void *info, int wait)
574 {
575 	unsigned long flags;
576 	int ret = 0;
577 
578 	preempt_disable();
579 	ret = smp_call_function(func, info, wait);
580 	local_irq_save(flags);
581 	func(info);
582 	local_irq_restore(flags);
583 	preempt_enable();
584 	return ret;
585 }
586 EXPORT_SYMBOL(on_each_cpu);
587 
588 /**
589  * on_each_cpu_mask(): Run a function on processors specified by
590  * cpumask, which may include the local processor.
591  * @mask: The set of cpus to run on (only runs on online subset).
592  * @func: The function to run. This must be fast and non-blocking.
593  * @info: An arbitrary pointer to pass to the function.
594  * @wait: If true, wait (atomically) until function has completed
595  *        on other CPUs.
596  *
597  * If @wait is true, then returns once @func has returned.
598  *
599  * You must not call this function with disabled interrupts or from a
600  * hardware interrupt handler or from a bottom half handler.  The
601  * exception is that it may be used during early boot while
602  * early_boot_irqs_disabled is set.
603  */
604 void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
605 			void *info, bool wait)
606 {
607 	int cpu = get_cpu();
608 
609 	smp_call_function_many(mask, func, info, wait);
610 	if (cpumask_test_cpu(cpu, mask)) {
611 		unsigned long flags;
612 		local_irq_save(flags);
613 		func(info);
614 		local_irq_restore(flags);
615 	}
616 	put_cpu();
617 }
618 EXPORT_SYMBOL(on_each_cpu_mask);
619 
620 /*
621  * on_each_cpu_cond(): Call a function on each processor for which
622  * the supplied function cond_func returns true, optionally waiting
623  * for all the required CPUs to finish. This may include the local
624  * processor.
625  * @cond_func:	A callback function that is passed a cpu id and
626  *		the the info parameter. The function is called
627  *		with preemption disabled. The function should
628  *		return a blooean value indicating whether to IPI
629  *		the specified CPU.
630  * @func:	The function to run on all applicable CPUs.
631  *		This must be fast and non-blocking.
632  * @info:	An arbitrary pointer to pass to both functions.
633  * @wait:	If true, wait (atomically) until function has
634  *		completed on other CPUs.
635  * @gfp_flags:	GFP flags to use when allocating the cpumask
636  *		used internally by the function.
637  *
638  * The function might sleep if the GFP flags indicates a non
639  * atomic allocation is allowed.
640  *
641  * Preemption is disabled to protect against CPUs going offline but not online.
642  * CPUs going online during the call will not be seen or sent an IPI.
643  *
644  * You must not call this function with disabled interrupts or
645  * from a hardware interrupt handler or from a bottom half handler.
646  */
647 void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
648 			smp_call_func_t func, void *info, bool wait,
649 			gfp_t gfp_flags)
650 {
651 	cpumask_var_t cpus;
652 	int cpu, ret;
653 
654 	might_sleep_if(gfp_flags & __GFP_WAIT);
655 
656 	if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
657 		preempt_disable();
658 		for_each_online_cpu(cpu)
659 			if (cond_func(cpu, info))
660 				cpumask_set_cpu(cpu, cpus);
661 		on_each_cpu_mask(cpus, func, info, wait);
662 		preempt_enable();
663 		free_cpumask_var(cpus);
664 	} else {
665 		/*
666 		 * No free cpumask, bother. No matter, we'll
667 		 * just have to IPI them one by one.
668 		 */
669 		preempt_disable();
670 		for_each_online_cpu(cpu)
671 			if (cond_func(cpu, info)) {
672 				ret = smp_call_function_single(cpu, func,
673 								info, wait);
674 				WARN_ON_ONCE(ret);
675 			}
676 		preempt_enable();
677 	}
678 }
679 EXPORT_SYMBOL(on_each_cpu_cond);
680 
681 static void do_nothing(void *unused)
682 {
683 }
684 
685 /**
686  * kick_all_cpus_sync - Force all cpus out of idle
687  *
688  * Used to synchronize the update of pm_idle function pointer. It's
689  * called after the pointer is updated and returns after the dummy
690  * callback function has been executed on all cpus. The execution of
691  * the function can only happen on the remote cpus after they have
692  * left the idle function which had been called via pm_idle function
693  * pointer. So it's guaranteed that nothing uses the previous pointer
694  * anymore.
695  */
696 void kick_all_cpus_sync(void)
697 {
698 	/* Make sure the change is visible before we kick the cpus */
699 	smp_mb();
700 	smp_call_function(do_nothing, NULL, 1);
701 }
702 EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
703 
704 /**
705  * wake_up_all_idle_cpus - break all cpus out of idle
706  * wake_up_all_idle_cpus try to break all cpus which is in idle state even
707  * including idle polling cpus, for non-idle cpus, we will do nothing
708  * for them.
709  */
710 void wake_up_all_idle_cpus(void)
711 {
712 	int cpu;
713 
714 	preempt_disable();
715 	for_each_online_cpu(cpu) {
716 		if (cpu == smp_processor_id())
717 			continue;
718 
719 		wake_up_if_idle(cpu);
720 	}
721 	preempt_enable();
722 }
723 EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);
724