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

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