smp.c 17.2 KB
Newer Older
1 2 3 4 5 6
/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
 */
#include <linux/rcupdate.h>
7
#include <linux/rculist.h>
8
#include <linux/kernel.h>
9
#include <linux/export.h>
I
Ingo Molnar 已提交
10 11
#include <linux/percpu.h>
#include <linux/init.h>
12
#include <linux/gfp.h>
13
#include <linux/smp.h>
P
Peter Zijlstra 已提交
14
#include <linux/cpu.h>
15

16 17
#include "smpboot.h"

18
enum {
19
	CSD_FLAG_LOCK		= 0x01,
20
	CSD_FLAG_WAIT		= 0x02,
21 22 23
};

struct call_function_data {
24
	struct call_single_data	__percpu *csd;
I
Ingo Molnar 已提交
25
	cpumask_var_t		cpumask;
26 27
};

28 29
static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);

30
static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);
P
Peter Zijlstra 已提交
31 32 33 34 35 36 37 38 39 40

static int
hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
{
	long cpu = (long)hcpu;
	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);

	switch (action) {
	case CPU_UP_PREPARE:
	case CPU_UP_PREPARE_FROZEN:
41
		if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
P
Peter Zijlstra 已提交
42
				cpu_to_node(cpu)))
43
			return notifier_from_errno(-ENOMEM);
44 45 46 47 48
		cfd->csd = alloc_percpu(struct call_single_data);
		if (!cfd->csd) {
			free_cpumask_var(cfd->cpumask);
			return notifier_from_errno(-ENOMEM);
		}
P
Peter Zijlstra 已提交
49 50
		break;

X
Xiao Guangrong 已提交
51
#ifdef CONFIG_HOTPLUG_CPU
P
Peter Zijlstra 已提交
52 53 54 55 56 57
	case CPU_UP_CANCELED:
	case CPU_UP_CANCELED_FROZEN:

	case CPU_DEAD:
	case CPU_DEAD_FROZEN:
		free_cpumask_var(cfd->cpumask);
58
		free_percpu(cfd->csd);
P
Peter Zijlstra 已提交
59 60 61 62 63 64 65
		break;
#endif
	};

	return NOTIFY_OK;
}

66
static struct notifier_block hotplug_cfd_notifier = {
I
Ingo Molnar 已提交
67
	.notifier_call		= hotplug_cfd,
P
Peter Zijlstra 已提交
68 69
};

70
void __init call_function_init(void)
71
{
P
Peter Zijlstra 已提交
72
	void *cpu = (void *)(long)smp_processor_id();
73 74
	int i;

75 76
	for_each_possible_cpu(i)
		init_llist_head(&per_cpu(call_single_queue, i));
P
Peter Zijlstra 已提交
77 78 79

	hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
	register_cpu_notifier(&hotplug_cfd_notifier);
80 81
}

P
Peter Zijlstra 已提交
82 83 84
/*
 * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
 *
I
Ingo Molnar 已提交
85 86 87
 * For non-synchronous ipi calls the csd can still be in use by the
 * previous function call. For multi-cpu calls its even more interesting
 * as we'll have to ensure no other cpu is observing our csd.
P
Peter Zijlstra 已提交
88
 */
A
Andrew Morton 已提交
89
static void csd_lock_wait(struct call_single_data *csd)
P
Peter Zijlstra 已提交
90
{
A
Andrew Morton 已提交
91
	while (csd->flags & CSD_FLAG_LOCK)
P
Peter Zijlstra 已提交
92
		cpu_relax();
93 94
}

A
Andrew Morton 已提交
95
static void csd_lock(struct call_single_data *csd)
96
{
A
Andrew Morton 已提交
97 98
	csd_lock_wait(csd);
	csd->flags |= CSD_FLAG_LOCK;
P
Peter Zijlstra 已提交
99 100

	/*
I
Ingo Molnar 已提交
101 102 103
	 * prevent CPU from reordering the above assignment
	 * to ->flags with any subsequent assignments to other
	 * fields of the specified call_single_data structure:
P
Peter Zijlstra 已提交
104 105 106 107
	 */
	smp_mb();
}

A
Andrew Morton 已提交
108
static void csd_unlock(struct call_single_data *csd)
P
Peter Zijlstra 已提交
109
{
110
	WARN_ON((csd->flags & CSD_FLAG_WAIT) && !(csd->flags & CSD_FLAG_LOCK));
I
Ingo Molnar 已提交
111

P
Peter Zijlstra 已提交
112
	/*
I
Ingo Molnar 已提交
113
	 * ensure we're all done before releasing data:
P
Peter Zijlstra 已提交
114 115
	 */
	smp_mb();
I
Ingo Molnar 已提交
116

A
Andrew Morton 已提交
117
	csd->flags &= ~CSD_FLAG_LOCK;
118 119
}

120 121
static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);

122
/*
I
Ingo Molnar 已提交
123 124 125
 * Insert a previously allocated call_single_data element
 * for execution on the given CPU. data must already have
 * ->func, ->info, and ->flags set.
126
 */
127 128
static int generic_exec_single(int cpu, struct call_single_data *csd,
			       smp_call_func_t func, void *info, int wait)
129
{
130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156
	struct call_single_data csd_stack = { .flags = 0 };
	unsigned long flags;


	if (cpu == smp_processor_id()) {
		local_irq_save(flags);
		func(info);
		local_irq_restore(flags);
		return 0;
	}


	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu))
		return -ENXIO;


	if (!csd) {
		csd = &csd_stack;
		if (!wait)
			csd = &__get_cpu_var(csd_data);
	}

	csd_lock(csd);

	csd->func = func;
	csd->info = info;

157 158 159
	if (wait)
		csd->flags |= CSD_FLAG_WAIT;

160
	/*
161 162 163 164 165 166 167
	 * The list addition should be visible before sending the IPI
	 * handler locks the list to pull the entry off it because of
	 * normal cache coherency rules implied by spinlocks.
	 *
	 * If IPIs can go out of order to the cache coherency protocol
	 * in an architecture, sufficient synchronisation should be added
	 * to arch code to make it appear to obey cache coherency WRT
I
Ingo Molnar 已提交
168 169
	 * locking and barrier primitives. Generic code isn't really
	 * equipped to do the right thing...
170
	 */
171
	if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
172 173 174
		arch_send_call_function_single_ipi(cpu);

	if (wait)
A
Andrew Morton 已提交
175
		csd_lock_wait(csd);
176 177

	return 0;
178 179 180
}

/*
I
Ingo Molnar 已提交
181 182
 * Invoked by arch to handle an IPI for call function single. Must be
 * called from the arch with interrupts disabled.
183 184 185
 */
void generic_smp_call_function_single_interrupt(void)
{
186 187
	struct llist_node *entry;
	struct call_single_data *csd, *csd_next;
188 189 190 191
	static bool warned;

	entry = llist_del_all(&__get_cpu_var(call_single_queue));
	entry = llist_reverse_order(entry);
192

193 194 195
	/*
	 * Shouldn't receive this interrupt on a cpu that is not yet online.
	 */
196 197 198 199 200 201 202 203 204 205 206 207
	if (unlikely(!cpu_online(smp_processor_id()) && !warned)) {
		warned = true;
		WARN(1, "IPI on offline CPU %d\n", smp_processor_id());

		/*
		 * We don't have to use the _safe() variant here
		 * because we are not invoking the IPI handlers yet.
		 */
		llist_for_each_entry(csd, entry, llist)
			pr_warn("IPI callback %pS sent to offline CPU\n",
				csd->func);
	}
208

209
	llist_for_each_entry_safe(csd, csd_next, entry, llist) {
A
Andrew Morton 已提交
210
		csd->func(csd->info);
211
		csd_unlock(csd);
212 213 214 215 216 217 218 219 220
	}
}

/*
 * smp_call_function_single - Run a function on a specific CPU
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait until function has completed on other CPUs.
 *
221
 * Returns 0 on success, else a negative status code.
222
 */
D
David Howells 已提交
223
int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
224
			     int wait)
225
{
I
Ingo Molnar 已提交
226
	int this_cpu;
227
	int err;
228

I
Ingo Molnar 已提交
229 230 231 232 233 234
	/*
	 * prevent preemption and reschedule on another processor,
	 * as well as CPU removal
	 */
	this_cpu = get_cpu();

235 236 237 238 239 240 241 242
	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
		     && !oops_in_progress);
243

244
	err = generic_exec_single(cpu, NULL, func, info, wait);
245 246

	put_cpu();
I
Ingo Molnar 已提交
247

248
	return err;
249 250 251
}
EXPORT_SYMBOL(smp_call_function_single);

252
/**
253 254
 * smp_call_function_single_async(): Run an asynchronous function on a
 * 			         specific CPU.
255 256 257
 * @cpu: The CPU to run on.
 * @csd: Pre-allocated and setup data structure
 *
258 259 260 261 262 263 264 265 266
 * Like smp_call_function_single(), but the call is asynchonous and
 * can thus be done from contexts with disabled interrupts.
 *
 * The caller passes his own pre-allocated data structure
 * (ie: embedded in an object) and is responsible for synchronizing it
 * such that the IPIs performed on the @csd are strictly serialized.
 *
 * NOTE: Be careful, there is unfortunately no current debugging facility to
 * validate the correctness of this serialization.
267
 */
268
int smp_call_function_single_async(int cpu, struct call_single_data *csd)
269 270 271
{
	int err = 0;

272 273 274
	preempt_disable();
	err = generic_exec_single(cpu, csd, csd->func, csd->info, 0);
	preempt_enable();
275 276 277

	return err;
}
278
EXPORT_SYMBOL_GPL(smp_call_function_single_async);
279

280 281 282 283 284 285 286 287 288 289 290 291 292 293 294
/*
 * smp_call_function_any - Run a function on any of the given cpus
 * @mask: The mask of cpus it can run on.
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait until function has completed.
 *
 * Returns 0 on success, else a negative status code (if no cpus were online).
 *
 * Selection preference:
 *	1) current cpu if in @mask
 *	2) any cpu of current node if in @mask
 *	3) any other online cpu in @mask
 */
int smp_call_function_any(const struct cpumask *mask,
D
David Howells 已提交
295
			  smp_call_func_t func, void *info, int wait)
296 297 298 299 300 301 302 303 304 305 306
{
	unsigned int cpu;
	const struct cpumask *nodemask;
	int ret;

	/* Try for same CPU (cheapest) */
	cpu = get_cpu();
	if (cpumask_test_cpu(cpu, mask))
		goto call;

	/* Try for same node. */
307
	nodemask = cpumask_of_node(cpu_to_node(cpu));
308 309 310 311 312 313 314 315 316 317 318 319 320 321 322
	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
		if (cpu_online(cpu))
			goto call;
	}

	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
	cpu = cpumask_any_and(mask, cpu_online_mask);
call:
	ret = smp_call_function_single(cpu, func, info, wait);
	put_cpu();
	return ret;
}
EXPORT_SYMBOL_GPL(smp_call_function_any);

323
/**
R
Rusty Russell 已提交
324 325
 * smp_call_function_many(): Run a function on a set of other CPUs.
 * @mask: The set of cpus to run on (only runs on online subset).
326 327
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
I
Ingo Molnar 已提交
328 329
 * @wait: If true, wait (atomically) until function has completed
 *        on other CPUs.
330
 *
331
 * If @wait is true, then returns once @func has returned.
332 333 334 335 336
 *
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler. Preemption
 * must be disabled when calling this function.
 */
R
Rusty Russell 已提交
337
void smp_call_function_many(const struct cpumask *mask,
D
David Howells 已提交
338
			    smp_call_func_t func, void *info, bool wait)
339
{
A
Andrew Morton 已提交
340
	struct call_function_data *cfd;
341
	int cpu, next_cpu, this_cpu = smp_processor_id();
342

343 344 345 346 347 348 349
	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
350
		     && !oops_in_progress && !early_boot_irqs_disabled);
351

352
	/* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */
R
Rusty Russell 已提交
353
	cpu = cpumask_first_and(mask, cpu_online_mask);
I
Ingo Molnar 已提交
354
	if (cpu == this_cpu)
R
Rusty Russell 已提交
355
		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
I
Ingo Molnar 已提交
356

R
Rusty Russell 已提交
357 358 359 360 361 362
	/* No online cpus?  We're done. */
	if (cpu >= nr_cpu_ids)
		return;

	/* Do we have another CPU which isn't us? */
	next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
I
Ingo Molnar 已提交
363
	if (next_cpu == this_cpu)
R
Rusty Russell 已提交
364 365 366 367 368 369
		next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);

	/* Fastpath: do that cpu by itself. */
	if (next_cpu >= nr_cpu_ids) {
		smp_call_function_single(cpu, func, info, wait);
		return;
370 371
	}

A
Andrew Morton 已提交
372
	cfd = &__get_cpu_var(cfd_data);
373

A
Andrew Morton 已提交
374 375
	cpumask_and(cfd->cpumask, mask, cpu_online_mask);
	cpumask_clear_cpu(this_cpu, cfd->cpumask);
376 377

	/* Some callers race with other cpus changing the passed mask */
A
Andrew Morton 已提交
378
	if (unlikely(!cpumask_weight(cfd->cpumask)))
379
		return;
380

A
Andrew Morton 已提交
381 382
	for_each_cpu(cpu, cfd->cpumask) {
		struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
383 384 385 386

		csd_lock(csd);
		csd->func = func;
		csd->info = info;
387
		llist_add(&csd->llist, &per_cpu(call_single_queue, cpu));
388
	}
389

390
	/* Send a message to all CPUs in the map */
391
	arch_send_call_function_ipi_mask(cfd->cpumask);
392

393
	if (wait) {
A
Andrew Morton 已提交
394 395 396 397
		for_each_cpu(cpu, cfd->cpumask) {
			struct call_single_data *csd;

			csd = per_cpu_ptr(cfd->csd, cpu);
398 399 400
			csd_lock_wait(csd);
		}
	}
401
}
R
Rusty Russell 已提交
402
EXPORT_SYMBOL(smp_call_function_many);
403 404 405 406 407

/**
 * smp_call_function(): Run a function on all other CPUs.
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
I
Ingo Molnar 已提交
408 409
 * @wait: If true, wait (atomically) until function has completed
 *        on other CPUs.
410
 *
R
Rusty Russell 已提交
411
 * Returns 0.
412 413
 *
 * If @wait is true, then returns once @func has returned; otherwise
414
 * it returns just before the target cpu calls @func.
415 416 417 418
 *
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler.
 */
D
David Howells 已提交
419
int smp_call_function(smp_call_func_t func, void *info, int wait)
420 421
{
	preempt_disable();
R
Rusty Russell 已提交
422
	smp_call_function_many(cpu_online_mask, func, info, wait);
423
	preempt_enable();
I
Ingo Molnar 已提交
424

R
Rusty Russell 已提交
425
	return 0;
426 427
}
EXPORT_SYMBOL(smp_call_function);
428

429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491
/* Setup configured maximum number of CPUs to activate */
unsigned int setup_max_cpus = NR_CPUS;
EXPORT_SYMBOL(setup_max_cpus);


/*
 * Setup routine for controlling SMP activation
 *
 * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 * activation entirely (the MPS table probe still happens, though).
 *
 * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 * greater than 0, limits the maximum number of CPUs activated in
 * SMP mode to <NUM>.
 */

void __weak arch_disable_smp_support(void) { }

static int __init nosmp(char *str)
{
	setup_max_cpus = 0;
	arch_disable_smp_support();

	return 0;
}

early_param("nosmp", nosmp);

/* this is hard limit */
static int __init nrcpus(char *str)
{
	int nr_cpus;

	get_option(&str, &nr_cpus);
	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
		nr_cpu_ids = nr_cpus;

	return 0;
}

early_param("nr_cpus", nrcpus);

static int __init maxcpus(char *str)
{
	get_option(&str, &setup_max_cpus);
	if (setup_max_cpus == 0)
		arch_disable_smp_support();

	return 0;
}

early_param("maxcpus", maxcpus);

/* Setup number of possible processor ids */
int nr_cpu_ids __read_mostly = NR_CPUS;
EXPORT_SYMBOL(nr_cpu_ids);

/* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
void __init setup_nr_cpu_ids(void)
{
	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
}

492 493 494 495 496
void __weak smp_announce(void)
{
	printk(KERN_INFO "Brought up %d CPUs\n", num_online_cpus());
}

497 498 499 500 501
/* Called by boot processor to activate the rest. */
void __init smp_init(void)
{
	unsigned int cpu;

502 503
	idle_threads_init();

504 505 506 507 508 509 510 511 512
	/* FIXME: This should be done in userspace --RR */
	for_each_present_cpu(cpu) {
		if (num_online_cpus() >= setup_max_cpus)
			break;
		if (!cpu_online(cpu))
			cpu_up(cpu);
	}

	/* Any cleanup work */
513
	smp_announce();
514 515 516
	smp_cpus_done(setup_max_cpus);
}

517
/*
518 519 520
 * Call a function on all processors.  May be used during early boot while
 * early_boot_irqs_disabled is set.  Use local_irq_save/restore() instead
 * of local_irq_disable/enable().
521 522 523
 */
int on_each_cpu(void (*func) (void *info), void *info, int wait)
{
524
	unsigned long flags;
525 526 527 528
	int ret = 0;

	preempt_disable();
	ret = smp_call_function(func, info, wait);
529
	local_irq_save(flags);
530
	func(info);
531
	local_irq_restore(flags);
532 533 534 535
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL(on_each_cpu);
536 537 538 539 540 541 542 543 544 545 546 547

/**
 * on_each_cpu_mask(): Run a function on processors specified by
 * cpumask, which may include the local processor.
 * @mask: The set of cpus to run on (only runs on online subset).
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait (atomically) until function has completed
 *        on other CPUs.
 *
 * If @wait is true, then returns once @func has returned.
 *
548 549 550 551
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler.  The
 * exception is that it may be used during early boot while
 * early_boot_irqs_disabled is set.
552 553 554 555 556 557 558 559
 */
void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
			void *info, bool wait)
{
	int cpu = get_cpu();

	smp_call_function_many(mask, func, info, wait);
	if (cpumask_test_cpu(cpu, mask)) {
560 561
		unsigned long flags;
		local_irq_save(flags);
562
		func(info);
563
		local_irq_restore(flags);
564 565 566 567
	}
	put_cpu();
}
EXPORT_SYMBOL(on_each_cpu_mask);
568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628

/*
 * on_each_cpu_cond(): Call a function on each processor for which
 * the supplied function cond_func returns true, optionally waiting
 * for all the required CPUs to finish. This may include the local
 * processor.
 * @cond_func:	A callback function that is passed a cpu id and
 *		the the info parameter. The function is called
 *		with preemption disabled. The function should
 *		return a blooean value indicating whether to IPI
 *		the specified CPU.
 * @func:	The function to run on all applicable CPUs.
 *		This must be fast and non-blocking.
 * @info:	An arbitrary pointer to pass to both functions.
 * @wait:	If true, wait (atomically) until function has
 *		completed on other CPUs.
 * @gfp_flags:	GFP flags to use when allocating the cpumask
 *		used internally by the function.
 *
 * The function might sleep if the GFP flags indicates a non
 * atomic allocation is allowed.
 *
 * Preemption is disabled to protect against CPUs going offline but not online.
 * CPUs going online during the call will not be seen or sent an IPI.
 *
 * You must not call this function with disabled interrupts or
 * from a hardware interrupt handler or from a bottom half handler.
 */
void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
			smp_call_func_t func, void *info, bool wait,
			gfp_t gfp_flags)
{
	cpumask_var_t cpus;
	int cpu, ret;

	might_sleep_if(gfp_flags & __GFP_WAIT);

	if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
		preempt_disable();
		for_each_online_cpu(cpu)
			if (cond_func(cpu, info))
				cpumask_set_cpu(cpu, cpus);
		on_each_cpu_mask(cpus, func, info, wait);
		preempt_enable();
		free_cpumask_var(cpus);
	} else {
		/*
		 * No free cpumask, bother. No matter, we'll
		 * just have to IPI them one by one.
		 */
		preempt_disable();
		for_each_online_cpu(cpu)
			if (cond_func(cpu, info)) {
				ret = smp_call_function_single(cpu, func,
								info, wait);
				WARN_ON_ONCE(!ret);
			}
		preempt_enable();
	}
}
EXPORT_SYMBOL(on_each_cpu_cond);
629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651

static void do_nothing(void *unused)
{
}

/**
 * kick_all_cpus_sync - Force all cpus out of idle
 *
 * Used to synchronize the update of pm_idle function pointer. It's
 * called after the pointer is updated and returns after the dummy
 * callback function has been executed on all cpus. The execution of
 * the function can only happen on the remote cpus after they have
 * left the idle function which had been called via pm_idle function
 * pointer. So it's guaranteed that nothing uses the previous pointer
 * anymore.
 */
void kick_all_cpus_sync(void)
{
	/* Make sure the change is visible before we kick the cpus */
	smp_mb();
	smp_call_function(do_nothing, NULL, 1);
}
EXPORT_SYMBOL_GPL(kick_all_cpus_sync);