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

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