xref: /openbmc/linux/kernel/smp.c (revision b6dcefde)
1 /*
2  * Generic helpers for smp ipi calls
3  *
4  * (C) Jens Axboe <jens.axboe@oracle.com> 2008
5  */
6 #include <linux/rcupdate.h>
7 #include <linux/rculist.h>
8 #include <linux/kernel.h>
9 #include <linux/module.h>
10 #include <linux/percpu.h>
11 #include <linux/init.h>
12 #include <linux/smp.h>
13 #include <linux/cpu.h>
14 
15 static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
16 
17 static struct {
18 	struct list_head	queue;
19 	raw_spinlock_t		lock;
20 } call_function __cacheline_aligned_in_smp =
21 	{
22 		.queue		= LIST_HEAD_INIT(call_function.queue),
23 		.lock		= __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),
24 	};
25 
26 enum {
27 	CSD_FLAG_LOCK		= 0x01,
28 };
29 
30 struct call_function_data {
31 	struct call_single_data	csd;
32 	atomic_t		refs;
33 	cpumask_var_t		cpumask;
34 };
35 
36 struct call_single_queue {
37 	struct list_head	list;
38 	raw_spinlock_t		lock;
39 };
40 
41 static DEFINE_PER_CPU(struct call_function_data, cfd_data);
42 
43 static int
44 hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
45 {
46 	long cpu = (long)hcpu;
47 	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
48 
49 	switch (action) {
50 	case CPU_UP_PREPARE:
51 	case CPU_UP_PREPARE_FROZEN:
52 		if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
53 				cpu_to_node(cpu)))
54 			return NOTIFY_BAD;
55 		break;
56 
57 #ifdef CONFIG_HOTPLUG_CPU
58 	case CPU_UP_CANCELED:
59 	case CPU_UP_CANCELED_FROZEN:
60 
61 	case CPU_DEAD:
62 	case CPU_DEAD_FROZEN:
63 		free_cpumask_var(cfd->cpumask);
64 		break;
65 #endif
66 	};
67 
68 	return NOTIFY_OK;
69 }
70 
71 static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
72 	.notifier_call		= hotplug_cfd,
73 };
74 
75 static int __cpuinit init_call_single_data(void)
76 {
77 	void *cpu = (void *)(long)smp_processor_id();
78 	int i;
79 
80 	for_each_possible_cpu(i) {
81 		struct call_single_queue *q = &per_cpu(call_single_queue, i);
82 
83 		raw_spin_lock_init(&q->lock);
84 		INIT_LIST_HEAD(&q->list);
85 	}
86 
87 	hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
88 	register_cpu_notifier(&hotplug_cfd_notifier);
89 
90 	return 0;
91 }
92 early_initcall(init_call_single_data);
93 
94 /*
95  * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
96  *
97  * For non-synchronous ipi calls the csd can still be in use by the
98  * previous function call. For multi-cpu calls its even more interesting
99  * as we'll have to ensure no other cpu is observing our csd.
100  */
101 static void csd_lock_wait(struct call_single_data *data)
102 {
103 	while (data->flags & CSD_FLAG_LOCK)
104 		cpu_relax();
105 }
106 
107 static void csd_lock(struct call_single_data *data)
108 {
109 	csd_lock_wait(data);
110 	data->flags = CSD_FLAG_LOCK;
111 
112 	/*
113 	 * prevent CPU from reordering the above assignment
114 	 * to ->flags with any subsequent assignments to other
115 	 * fields of the specified call_single_data structure:
116 	 */
117 	smp_mb();
118 }
119 
120 static void csd_unlock(struct call_single_data *data)
121 {
122 	WARN_ON(!(data->flags & CSD_FLAG_LOCK));
123 
124 	/*
125 	 * ensure we're all done before releasing data:
126 	 */
127 	smp_mb();
128 
129 	data->flags &= ~CSD_FLAG_LOCK;
130 }
131 
132 /*
133  * Insert a previously allocated call_single_data element
134  * for execution on the given CPU. data must already have
135  * ->func, ->info, and ->flags set.
136  */
137 static
138 void generic_exec_single(int cpu, struct call_single_data *data, int wait)
139 {
140 	struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
141 	unsigned long flags;
142 	int ipi;
143 
144 	raw_spin_lock_irqsave(&dst->lock, flags);
145 	ipi = list_empty(&dst->list);
146 	list_add_tail(&data->list, &dst->list);
147 	raw_spin_unlock_irqrestore(&dst->lock, flags);
148 
149 	/*
150 	 * The list addition should be visible before sending the IPI
151 	 * handler locks the list to pull the entry off it because of
152 	 * normal cache coherency rules implied by spinlocks.
153 	 *
154 	 * If IPIs can go out of order to the cache coherency protocol
155 	 * in an architecture, sufficient synchronisation should be added
156 	 * to arch code to make it appear to obey cache coherency WRT
157 	 * locking and barrier primitives. Generic code isn't really
158 	 * equipped to do the right thing...
159 	 */
160 	if (ipi)
161 		arch_send_call_function_single_ipi(cpu);
162 
163 	if (wait)
164 		csd_lock_wait(data);
165 }
166 
167 /*
168  * Invoked by arch to handle an IPI for call function. Must be called with
169  * interrupts disabled.
170  */
171 void generic_smp_call_function_interrupt(void)
172 {
173 	struct call_function_data *data;
174 	int cpu = smp_processor_id();
175 
176 	/*
177 	 * Shouldn't receive this interrupt on a cpu that is not yet online.
178 	 */
179 	WARN_ON_ONCE(!cpu_online(cpu));
180 
181 	/*
182 	 * Ensure entry is visible on call_function_queue after we have
183 	 * entered the IPI. See comment in smp_call_function_many.
184 	 * If we don't have this, then we may miss an entry on the list
185 	 * and never get another IPI to process it.
186 	 */
187 	smp_mb();
188 
189 	/*
190 	 * It's ok to use list_for_each_rcu() here even though we may
191 	 * delete 'pos', since list_del_rcu() doesn't clear ->next
192 	 */
193 	list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
194 		int refs;
195 
196 		if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
197 			continue;
198 
199 		data->csd.func(data->csd.info);
200 
201 		refs = atomic_dec_return(&data->refs);
202 		WARN_ON(refs < 0);
203 		if (!refs) {
204 			raw_spin_lock(&call_function.lock);
205 			list_del_rcu(&data->csd.list);
206 			raw_spin_unlock(&call_function.lock);
207 		}
208 
209 		if (refs)
210 			continue;
211 
212 		csd_unlock(&data->csd);
213 	}
214 
215 }
216 
217 /*
218  * Invoked by arch to handle an IPI for call function single. Must be
219  * called from the arch with interrupts disabled.
220  */
221 void generic_smp_call_function_single_interrupt(void)
222 {
223 	struct call_single_queue *q = &__get_cpu_var(call_single_queue);
224 	unsigned int data_flags;
225 	LIST_HEAD(list);
226 
227 	/*
228 	 * Shouldn't receive this interrupt on a cpu that is not yet online.
229 	 */
230 	WARN_ON_ONCE(!cpu_online(smp_processor_id()));
231 
232 	raw_spin_lock(&q->lock);
233 	list_replace_init(&q->list, &list);
234 	raw_spin_unlock(&q->lock);
235 
236 	while (!list_empty(&list)) {
237 		struct call_single_data *data;
238 
239 		data = list_entry(list.next, struct call_single_data, list);
240 		list_del(&data->list);
241 
242 		/*
243 		 * 'data' can be invalid after this call if flags == 0
244 		 * (when called through generic_exec_single()),
245 		 * so save them away before making the call:
246 		 */
247 		data_flags = data->flags;
248 
249 		data->func(data->info);
250 
251 		/*
252 		 * Unlocked CSDs are valid through generic_exec_single():
253 		 */
254 		if (data_flags & CSD_FLAG_LOCK)
255 			csd_unlock(data);
256 	}
257 }
258 
259 static DEFINE_PER_CPU(struct call_single_data, csd_data);
260 
261 /*
262  * smp_call_function_single - Run a function on a specific CPU
263  * @func: The function to run. This must be fast and non-blocking.
264  * @info: An arbitrary pointer to pass to the function.
265  * @wait: If true, wait until function has completed on other CPUs.
266  *
267  * Returns 0 on success, else a negative status code.
268  */
269 int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
270 			     int wait)
271 {
272 	struct call_single_data d = {
273 		.flags = 0,
274 	};
275 	unsigned long flags;
276 	int this_cpu;
277 	int err = 0;
278 
279 	/*
280 	 * prevent preemption and reschedule on another processor,
281 	 * as well as CPU removal
282 	 */
283 	this_cpu = get_cpu();
284 
285 	/*
286 	 * Can deadlock when called with interrupts disabled.
287 	 * We allow cpu's that are not yet online though, as no one else can
288 	 * send smp call function interrupt to this cpu and as such deadlocks
289 	 * can't happen.
290 	 */
291 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
292 		     && !oops_in_progress);
293 
294 	if (cpu == this_cpu) {
295 		local_irq_save(flags);
296 		func(info);
297 		local_irq_restore(flags);
298 	} else {
299 		if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
300 			struct call_single_data *data = &d;
301 
302 			if (!wait)
303 				data = &__get_cpu_var(csd_data);
304 
305 			csd_lock(data);
306 
307 			data->func = func;
308 			data->info = info;
309 			generic_exec_single(cpu, data, wait);
310 		} else {
311 			err = -ENXIO;	/* CPU not online */
312 		}
313 	}
314 
315 	put_cpu();
316 
317 	return err;
318 }
319 EXPORT_SYMBOL(smp_call_function_single);
320 
321 /*
322  * smp_call_function_any - Run a function on any of the given cpus
323  * @mask: The mask of cpus it can run on.
324  * @func: The function to run. This must be fast and non-blocking.
325  * @info: An arbitrary pointer to pass to the function.
326  * @wait: If true, wait until function has completed.
327  *
328  * Returns 0 on success, else a negative status code (if no cpus were online).
329  * Note that @wait will be implicitly turned on in case of allocation failures,
330  * since we fall back to on-stack allocation.
331  *
332  * Selection preference:
333  *	1) current cpu if in @mask
334  *	2) any cpu of current node if in @mask
335  *	3) any other online cpu in @mask
336  */
337 int smp_call_function_any(const struct cpumask *mask,
338 			  void (*func)(void *info), void *info, int wait)
339 {
340 	unsigned int cpu;
341 	const struct cpumask *nodemask;
342 	int ret;
343 
344 	/* Try for same CPU (cheapest) */
345 	cpu = get_cpu();
346 	if (cpumask_test_cpu(cpu, mask))
347 		goto call;
348 
349 	/* Try for same node. */
350 	nodemask = cpumask_of_node(cpu_to_node(cpu));
351 	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
352 	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
353 		if (cpu_online(cpu))
354 			goto call;
355 	}
356 
357 	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
358 	cpu = cpumask_any_and(mask, cpu_online_mask);
359 call:
360 	ret = smp_call_function_single(cpu, func, info, wait);
361 	put_cpu();
362 	return ret;
363 }
364 EXPORT_SYMBOL_GPL(smp_call_function_any);
365 
366 /**
367  * __smp_call_function_single(): Run a function on another CPU
368  * @cpu: The CPU to run on.
369  * @data: Pre-allocated and setup data structure
370  *
371  * Like smp_call_function_single(), but allow caller to pass in a
372  * pre-allocated data structure. Useful for embedding @data inside
373  * other structures, for instance.
374  */
375 void __smp_call_function_single(int cpu, struct call_single_data *data,
376 				int wait)
377 {
378 	csd_lock(data);
379 
380 	/*
381 	 * Can deadlock when called with interrupts disabled.
382 	 * We allow cpu's that are not yet online though, as no one else can
383 	 * send smp call function interrupt to this cpu and as such deadlocks
384 	 * can't happen.
385 	 */
386 	WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
387 		     && !oops_in_progress);
388 
389 	generic_exec_single(cpu, data, wait);
390 }
391 
392 /**
393  * smp_call_function_many(): Run a function on a set of other CPUs.
394  * @mask: The set of cpus to run on (only runs on online subset).
395  * @func: The function to run. This must be fast and non-blocking.
396  * @info: An arbitrary pointer to pass to the function.
397  * @wait: If true, wait (atomically) until function has completed
398  *        on other CPUs.
399  *
400  * If @wait is true, then returns once @func has returned.
401  *
402  * You must not call this function with disabled interrupts or from a
403  * hardware interrupt handler or from a bottom half handler. Preemption
404  * must be disabled when calling this function.
405  */
406 void smp_call_function_many(const struct cpumask *mask,
407 			    void (*func)(void *), void *info, bool wait)
408 {
409 	struct call_function_data *data;
410 	unsigned long flags;
411 	int cpu, next_cpu, this_cpu = smp_processor_id();
412 
413 	/*
414 	 * Can deadlock when called with interrupts disabled.
415 	 * We allow cpu's that are not yet online though, as no one else can
416 	 * send smp call function interrupt to this cpu and as such deadlocks
417 	 * can't happen.
418 	 */
419 	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
420 		     && !oops_in_progress);
421 
422 	/* So, what's a CPU they want? Ignoring this one. */
423 	cpu = cpumask_first_and(mask, cpu_online_mask);
424 	if (cpu == this_cpu)
425 		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
426 
427 	/* No online cpus?  We're done. */
428 	if (cpu >= nr_cpu_ids)
429 		return;
430 
431 	/* Do we have another CPU which isn't us? */
432 	next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
433 	if (next_cpu == this_cpu)
434 		next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
435 
436 	/* Fastpath: do that cpu by itself. */
437 	if (next_cpu >= nr_cpu_ids) {
438 		smp_call_function_single(cpu, func, info, wait);
439 		return;
440 	}
441 
442 	data = &__get_cpu_var(cfd_data);
443 	csd_lock(&data->csd);
444 
445 	data->csd.func = func;
446 	data->csd.info = info;
447 	cpumask_and(data->cpumask, mask, cpu_online_mask);
448 	cpumask_clear_cpu(this_cpu, data->cpumask);
449 	atomic_set(&data->refs, cpumask_weight(data->cpumask));
450 
451 	raw_spin_lock_irqsave(&call_function.lock, flags);
452 	/*
453 	 * Place entry at the _HEAD_ of the list, so that any cpu still
454 	 * observing the entry in generic_smp_call_function_interrupt()
455 	 * will not miss any other list entries:
456 	 */
457 	list_add_rcu(&data->csd.list, &call_function.queue);
458 	raw_spin_unlock_irqrestore(&call_function.lock, flags);
459 
460 	/*
461 	 * Make the list addition visible before sending the ipi.
462 	 * (IPIs must obey or appear to obey normal Linux cache
463 	 * coherency rules -- see comment in generic_exec_single).
464 	 */
465 	smp_mb();
466 
467 	/* Send a message to all CPUs in the map */
468 	arch_send_call_function_ipi_mask(data->cpumask);
469 
470 	/* Optionally wait for the CPUs to complete */
471 	if (wait)
472 		csd_lock_wait(&data->csd);
473 }
474 EXPORT_SYMBOL(smp_call_function_many);
475 
476 /**
477  * smp_call_function(): Run a function on all other CPUs.
478  * @func: The function to run. This must be fast and non-blocking.
479  * @info: An arbitrary pointer to pass to the function.
480  * @wait: If true, wait (atomically) until function has completed
481  *        on other CPUs.
482  *
483  * Returns 0.
484  *
485  * If @wait is true, then returns once @func has returned; otherwise
486  * it returns just before the target cpu calls @func.
487  *
488  * You must not call this function with disabled interrupts or from a
489  * hardware interrupt handler or from a bottom half handler.
490  */
491 int smp_call_function(void (*func)(void *), void *info, int wait)
492 {
493 	preempt_disable();
494 	smp_call_function_many(cpu_online_mask, func, info, wait);
495 	preempt_enable();
496 
497 	return 0;
498 }
499 EXPORT_SYMBOL(smp_call_function);
500 
501 void ipi_call_lock(void)
502 {
503 	raw_spin_lock(&call_function.lock);
504 }
505 
506 void ipi_call_unlock(void)
507 {
508 	raw_spin_unlock(&call_function.lock);
509 }
510 
511 void ipi_call_lock_irq(void)
512 {
513 	raw_spin_lock_irq(&call_function.lock);
514 }
515 
516 void ipi_call_unlock_irq(void)
517 {
518 	raw_spin_unlock_irq(&call_function.lock);
519 }
520