Root/kernel/smp.c

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/gfp.h>
13#include <linux/smp.h>
14#include <linux/cpu.h>
15
16static struct {
17    struct list_head queue;
18    raw_spinlock_t lock;
19} call_function __cacheline_aligned_in_smp =
20    {
21        .queue = LIST_HEAD_INIT(call_function.queue),
22        .lock = __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),
23    };
24
25enum {
26    CSD_FLAG_LOCK = 0x01,
27};
28
29struct call_function_data {
30    struct call_single_data csd;
31    atomic_t refs;
32    cpumask_var_t cpumask;
33};
34
35static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
36
37struct call_single_queue {
38    struct list_head list;
39    raw_spinlock_t lock;
40};
41
42static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);
43
44static int
45hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
46{
47    long cpu = (long)hcpu;
48    struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
49
50    switch (action) {
51    case CPU_UP_PREPARE:
52    case CPU_UP_PREPARE_FROZEN:
53        if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
54                cpu_to_node(cpu)))
55            return notifier_from_errno(-ENOMEM);
56        break;
57
58#ifdef CONFIG_HOTPLUG_CPU
59    case CPU_UP_CANCELED:
60    case CPU_UP_CANCELED_FROZEN:
61
62    case CPU_DEAD:
63    case CPU_DEAD_FROZEN:
64        free_cpumask_var(cfd->cpumask);
65        break;
66#endif
67    };
68
69    return NOTIFY_OK;
70}
71
72static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
73    .notifier_call = hotplug_cfd,
74};
75
76static int __cpuinit init_call_single_data(void)
77{
78    void *cpu = (void *)(long)smp_processor_id();
79    int i;
80
81    for_each_possible_cpu(i) {
82        struct call_single_queue *q = &per_cpu(call_single_queue, i);
83
84        raw_spin_lock_init(&q->lock);
85        INIT_LIST_HEAD(&q->list);
86    }
87
88    hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
89    register_cpu_notifier(&hotplug_cfd_notifier);
90
91    return 0;
92}
93early_initcall(init_call_single_data);
94
95/*
96 * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
97 *
98 * For non-synchronous ipi calls the csd can still be in use by the
99 * previous function call. For multi-cpu calls its even more interesting
100 * as we'll have to ensure no other cpu is observing our csd.
101 */
102static void csd_lock_wait(struct call_single_data *data)
103{
104    while (data->flags & CSD_FLAG_LOCK)
105        cpu_relax();
106}
107
108static void csd_lock(struct call_single_data *data)
109{
110    csd_lock_wait(data);
111    data->flags = CSD_FLAG_LOCK;
112
113    /*
114     * prevent CPU from reordering the above assignment
115     * to ->flags with any subsequent assignments to other
116     * fields of the specified call_single_data structure:
117     */
118    smp_mb();
119}
120
121static void csd_unlock(struct call_single_data *data)
122{
123    WARN_ON(!(data->flags & CSD_FLAG_LOCK));
124
125    /*
126     * ensure we're all done before releasing data:
127     */
128    smp_mb();
129
130    data->flags &= ~CSD_FLAG_LOCK;
131}
132
133/*
134 * Insert a previously allocated call_single_data element
135 * for execution on the given CPU. data must already have
136 * ->func, ->info, and ->flags set.
137 */
138static
139void generic_exec_single(int cpu, struct call_single_data *data, int wait)
140{
141    struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
142    unsigned long flags;
143    int ipi;
144
145    raw_spin_lock_irqsave(&dst->lock, flags);
146    ipi = list_empty(&dst->list);
147    list_add_tail(&data->list, &dst->list);
148    raw_spin_unlock_irqrestore(&dst->lock, flags);
149
150    /*
151     * The list addition should be visible before sending the IPI
152     * handler locks the list to pull the entry off it because of
153     * normal cache coherency rules implied by spinlocks.
154     *
155     * If IPIs can go out of order to the cache coherency protocol
156     * in an architecture, sufficient synchronisation should be added
157     * to arch code to make it appear to obey cache coherency WRT
158     * locking and barrier primitives. Generic code isn't really
159     * equipped to do the right thing...
160     */
161    if (ipi)
162        arch_send_call_function_single_ipi(cpu);
163
164    if (wait)
165        csd_lock_wait(data);
166}
167
168/*
169 * Invoked by arch to handle an IPI for call function. Must be called with
170 * interrupts disabled.
171 */
172void generic_smp_call_function_interrupt(void)
173{
174    struct call_function_data *data;
175    int cpu = smp_processor_id();
176
177    /*
178     * Shouldn't receive this interrupt on a cpu that is not yet online.
179     */
180    WARN_ON_ONCE(!cpu_online(cpu));
181
182    /*
183     * Ensure entry is visible on call_function_queue after we have
184     * entered the IPI. See comment in smp_call_function_many.
185     * If we don't have this, then we may miss an entry on the list
186     * and never get another IPI to process it.
187     */
188    smp_mb();
189
190    /*
191     * It's ok to use list_for_each_rcu() here even though we may
192     * delete 'pos', since list_del_rcu() doesn't clear ->next
193     */
194    list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
195        int refs;
196
197        if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
198            continue;
199
200        data->csd.func(data->csd.info);
201
202        refs = atomic_dec_return(&data->refs);
203        WARN_ON(refs < 0);
204        if (!refs) {
205            raw_spin_lock(&call_function.lock);
206            list_del_rcu(&data->csd.list);
207            raw_spin_unlock(&call_function.lock);
208        }
209
210        if (refs)
211            continue;
212
213        csd_unlock(&data->csd);
214    }
215
216}
217
218/*
219 * Invoked by arch to handle an IPI for call function single. Must be
220 * called from the arch with interrupts disabled.
221 */
222void generic_smp_call_function_single_interrupt(void)
223{
224    struct call_single_queue *q = &__get_cpu_var(call_single_queue);
225    unsigned int data_flags;
226    LIST_HEAD(list);
227
228    /*
229     * Shouldn't receive this interrupt on a cpu that is not yet online.
230     */
231    WARN_ON_ONCE(!cpu_online(smp_processor_id()));
232
233    raw_spin_lock(&q->lock);
234    list_replace_init(&q->list, &list);
235    raw_spin_unlock(&q->lock);
236
237    while (!list_empty(&list)) {
238        struct call_single_data *data;
239
240        data = list_entry(list.next, struct call_single_data, list);
241        list_del(&data->list);
242
243        /*
244         * 'data' can be invalid after this call if flags == 0
245         * (when called through generic_exec_single()),
246         * so save them away before making the call:
247         */
248        data_flags = data->flags;
249
250        data->func(data->info);
251
252        /*
253         * Unlocked CSDs are valid through generic_exec_single():
254         */
255        if (data_flags & CSD_FLAG_LOCK)
256            csd_unlock(data);
257    }
258}
259
260static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
261
262/*
263 * smp_call_function_single - Run a function on a specific CPU
264 * @func: The function to run. This must be fast and non-blocking.
265 * @info: An arbitrary pointer to pass to the function.
266 * @wait: If true, wait until function has completed on other CPUs.
267 *
268 * Returns 0 on success, else a negative status code.
269 */
270int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
271                 int wait)
272{
273    struct call_single_data d = {
274        .flags = 0,
275    };
276    unsigned long flags;
277    int this_cpu;
278    int err = 0;
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    if (cpu == this_cpu) {
296        local_irq_save(flags);
297        func(info);
298        local_irq_restore(flags);
299    } else {
300        if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
301            struct call_single_data *data = &d;
302
303            if (!wait)
304                data = &__get_cpu_var(csd_data);
305
306            csd_lock(data);
307
308            data->func = func;
309            data->info = info;
310            generic_exec_single(cpu, data, wait);
311        } else {
312            err = -ENXIO; /* CPU not online */
313        }
314    }
315
316    put_cpu();
317
318    return err;
319}
320EXPORT_SYMBOL(smp_call_function_single);
321
322/*
323 * smp_call_function_any - Run a function on any of the given cpus
324 * @mask: The mask of cpus it can run on.
325 * @func: The function to run. This must be fast and non-blocking.
326 * @info: An arbitrary pointer to pass to the function.
327 * @wait: If true, wait until function has completed.
328 *
329 * Returns 0 on success, else a negative status code (if no cpus were online).
330 * Note that @wait will be implicitly turned on in case of allocation failures,
331 * since we fall back to on-stack allocation.
332 *
333 * Selection preference:
334 * 1) current cpu if in @mask
335 * 2) any cpu of current node if in @mask
336 * 3) any other online cpu in @mask
337 */
338int smp_call_function_any(const struct cpumask *mask,
339              void (*func)(void *info), void *info, int wait)
340{
341    unsigned int cpu;
342    const struct cpumask *nodemask;
343    int ret;
344
345    /* Try for same CPU (cheapest) */
346    cpu = get_cpu();
347    if (cpumask_test_cpu(cpu, mask))
348        goto call;
349
350    /* Try for same node. */
351    nodemask = cpumask_of_node(cpu_to_node(cpu));
352    for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
353         cpu = cpumask_next_and(cpu, nodemask, mask)) {
354        if (cpu_online(cpu))
355            goto call;
356    }
357
358    /* Any online will do: smp_call_function_single handles nr_cpu_ids. */
359    cpu = cpumask_any_and(mask, cpu_online_mask);
360call:
361    ret = smp_call_function_single(cpu, func, info, wait);
362    put_cpu();
363    return ret;
364}
365EXPORT_SYMBOL_GPL(smp_call_function_any);
366
367/**
368 * __smp_call_function_single(): Run a function on a specific CPU
369 * @cpu: The CPU to run on.
370 * @data: Pre-allocated and setup data structure
371 * @wait: If true, wait until function has completed on specified CPU.
372 *
373 * Like smp_call_function_single(), but allow caller to pass in a
374 * pre-allocated data structure. Useful for embedding @data inside
375 * other structures, for instance.
376 */
377void __smp_call_function_single(int cpu, struct call_single_data *data,
378                int wait)
379{
380    unsigned int this_cpu;
381    unsigned long flags;
382
383    this_cpu = get_cpu();
384    /*
385     * Can deadlock when called with interrupts disabled.
386     * We allow cpu's that are not yet online though, as no one else can
387     * send smp call function interrupt to this cpu and as such deadlocks
388     * can't happen.
389     */
390    WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
391             && !oops_in_progress);
392
393    if (cpu == this_cpu) {
394        local_irq_save(flags);
395        data->func(data->info);
396        local_irq_restore(flags);
397    } else {
398        csd_lock(data);
399        generic_exec_single(cpu, data, wait);
400    }
401    put_cpu();
402}
403
404/**
405 * smp_call_function_many(): Run a function on a set of other CPUs.
406 * @mask: The set of cpus to run on (only runs on online subset).
407 * @func: The function to run. This must be fast and non-blocking.
408 * @info: An arbitrary pointer to pass to the function.
409 * @wait: If true, wait (atomically) until function has completed
410 * on other CPUs.
411 *
412 * If @wait is true, then returns once @func has returned.
413 *
414 * You must not call this function with disabled interrupts or from a
415 * hardware interrupt handler or from a bottom half handler. Preemption
416 * must be disabled when calling this function.
417 */
418void smp_call_function_many(const struct cpumask *mask,
419                void (*func)(void *), void *info, bool wait)
420{
421    struct call_function_data *data;
422    unsigned long flags;
423    int cpu, next_cpu, this_cpu = smp_processor_id();
424
425    /*
426     * Can deadlock when called with interrupts disabled.
427     * We allow cpu's that are not yet online though, as no one else can
428     * send smp call function interrupt to this cpu and as such deadlocks
429     * can't happen.
430     */
431    WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
432             && !oops_in_progress);
433
434    /* So, what's a CPU they want? Ignoring this one. */
435    cpu = cpumask_first_and(mask, cpu_online_mask);
436    if (cpu == this_cpu)
437        cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
438
439    /* No online cpus? We're done. */
440    if (cpu >= nr_cpu_ids)
441        return;
442
443    /* Do we have another CPU which isn't us? */
444    next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
445    if (next_cpu == this_cpu)
446        next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
447
448    /* Fastpath: do that cpu by itself. */
449    if (next_cpu >= nr_cpu_ids) {
450        smp_call_function_single(cpu, func, info, wait);
451        return;
452    }
453
454    data = &__get_cpu_var(cfd_data);
455    csd_lock(&data->csd);
456
457    data->csd.func = func;
458    data->csd.info = info;
459    cpumask_and(data->cpumask, mask, cpu_online_mask);
460    cpumask_clear_cpu(this_cpu, data->cpumask);
461    atomic_set(&data->refs, cpumask_weight(data->cpumask));
462
463    raw_spin_lock_irqsave(&call_function.lock, flags);
464    /*
465     * Place entry at the _HEAD_ of the list, so that any cpu still
466     * observing the entry in generic_smp_call_function_interrupt()
467     * will not miss any other list entries:
468     */
469    list_add_rcu(&data->csd.list, &call_function.queue);
470    raw_spin_unlock_irqrestore(&call_function.lock, flags);
471
472    /*
473     * Make the list addition visible before sending the ipi.
474     * (IPIs must obey or appear to obey normal Linux cache
475     * coherency rules -- see comment in generic_exec_single).
476     */
477    smp_mb();
478
479    /* Send a message to all CPUs in the map */
480    arch_send_call_function_ipi_mask(data->cpumask);
481
482    /* Optionally wait for the CPUs to complete */
483    if (wait)
484        csd_lock_wait(&data->csd);
485}
486EXPORT_SYMBOL(smp_call_function_many);
487
488/**
489 * smp_call_function(): Run a function on all other CPUs.
490 * @func: The function to run. This must be fast and non-blocking.
491 * @info: An arbitrary pointer to pass to the function.
492 * @wait: If true, wait (atomically) until function has completed
493 * on other CPUs.
494 *
495 * Returns 0.
496 *
497 * If @wait is true, then returns once @func has returned; otherwise
498 * it returns just before the target cpu calls @func.
499 *
500 * You must not call this function with disabled interrupts or from a
501 * hardware interrupt handler or from a bottom half handler.
502 */
503int smp_call_function(void (*func)(void *), void *info, int wait)
504{
505    preempt_disable();
506    smp_call_function_many(cpu_online_mask, func, info, wait);
507    preempt_enable();
508
509    return 0;
510}
511EXPORT_SYMBOL(smp_call_function);
512
513void ipi_call_lock(void)
514{
515    raw_spin_lock(&call_function.lock);
516}
517
518void ipi_call_unlock(void)
519{
520    raw_spin_unlock(&call_function.lock);
521}
522
523void ipi_call_lock_irq(void)
524{
525    raw_spin_lock_irq(&call_function.lock);
526}
527
528void ipi_call_unlock_irq(void)
529{
530    raw_spin_unlock_irq(&call_function.lock);
531}
532

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