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/smp.h>
13#include <linux/cpu.h>
14
15static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
16
17static struct {
18    struct list_head queue;
19    spinlock_t lock;
20} call_function __cacheline_aligned_in_smp =
21    {
22        .queue = LIST_HEAD_INIT(call_function.queue),
23        .lock = __SPIN_LOCK_UNLOCKED(call_function.lock),
24    };
25
26enum {
27    CSD_FLAG_LOCK = 0x01,
28};
29
30struct call_function_data {
31    struct call_single_data csd;
32    atomic_t refs;
33    cpumask_var_t cpumask;
34};
35
36struct call_single_queue {
37    struct list_head list;
38    spinlock_t lock;
39};
40
41static DEFINE_PER_CPU(struct call_function_data, cfd_data);
42
43static int
44hotplug_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
71static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
72    .notifier_call = hotplug_cfd,
73};
74
75static 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        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}
92early_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 */
101static void csd_lock_wait(struct call_single_data *data)
102{
103    while (data->flags & CSD_FLAG_LOCK)
104        cpu_relax();
105}
106
107static 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
120static 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 */
137static
138void 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    spin_lock_irqsave(&dst->lock, flags);
145    ipi = list_empty(&dst->list);
146    list_add_tail(&data->list, &dst->list);
147    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 */
171void generic_smp_call_function_interrupt(void)
172{
173    struct call_function_data *data;
174    int cpu = get_cpu();
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            spin_lock(&call_function.lock);
205            list_del_rcu(&data->csd.list);
206            spin_unlock(&call_function.lock);
207        }
208
209        if (refs)
210            continue;
211
212        csd_unlock(&data->csd);
213    }
214
215    put_cpu();
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    spin_lock(&q->lock);
234    list_replace_init(&q->list, &list);
235    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(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. Note that @wait
269 * will be implicitly turned on in case of allocation failures, since
270 * we fall back to on-stack allocation.
271 */
272int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
273                 int wait)
274{
275    struct call_single_data d = {
276        .flags = 0,
277    };
278    unsigned long flags;
279    int this_cpu;
280    int err = 0;
281
282    /*
283     * prevent preemption and reschedule on another processor,
284     * as well as CPU removal
285     */
286    this_cpu = get_cpu();
287
288    /*
289     * Can deadlock when called with interrupts disabled.
290     * We allow cpu's that are not yet online though, as no one else can
291     * send smp call function interrupt to this cpu and as such deadlocks
292     * can't happen.
293     */
294    WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
295             && !oops_in_progress);
296
297    if (cpu == this_cpu) {
298        local_irq_save(flags);
299        func(info);
300        local_irq_restore(flags);
301    } else {
302        if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
303            struct call_single_data *data = &d;
304
305            if (!wait)
306                data = &__get_cpu_var(csd_data);
307
308            csd_lock(data);
309
310            data->func = func;
311            data->info = info;
312            generic_exec_single(cpu, data, wait);
313        } else {
314            err = -ENXIO; /* CPU not online */
315        }
316    }
317
318    put_cpu();
319
320    return err;
321}
322EXPORT_SYMBOL(smp_call_function_single);
323
324/**
325 * __smp_call_function_single(): Run a function on another CPU
326 * @cpu: The CPU to run on.
327 * @data: Pre-allocated and setup data structure
328 *
329 * Like smp_call_function_single(), but allow caller to pass in a
330 * pre-allocated data structure. Useful for embedding @data inside
331 * other structures, for instance.
332 */
333void __smp_call_function_single(int cpu, struct call_single_data *data,
334                int wait)
335{
336    csd_lock(data);
337
338    /*
339     * Can deadlock when called with interrupts disabled.
340     * We allow cpu's that are not yet online though, as no one else can
341     * send smp call function interrupt to this cpu and as such deadlocks
342     * can't happen.
343     */
344    WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
345             && !oops_in_progress);
346
347    generic_exec_single(cpu, data, wait);
348}
349
350/**
351 * smp_call_function_many(): Run a function on a set of other CPUs.
352 * @mask: The set of cpus to run on (only runs on online subset).
353 * @func: The function to run. This must be fast and non-blocking.
354 * @info: An arbitrary pointer to pass to the function.
355 * @wait: If true, wait (atomically) until function has completed
356 * on other CPUs.
357 *
358 * If @wait is true, then returns once @func has returned. Note that @wait
359 * will be implicitly turned on in case of allocation failures, since
360 * we fall back to on-stack allocation.
361 *
362 * You must not call this function with disabled interrupts or from a
363 * hardware interrupt handler or from a bottom half handler. Preemption
364 * must be disabled when calling this function.
365 */
366void smp_call_function_many(const struct cpumask *mask,
367                void (*func)(void *), void *info, bool wait)
368{
369    struct call_function_data *data;
370    unsigned long flags;
371    int cpu, next_cpu, this_cpu = smp_processor_id();
372
373    /*
374     * Can deadlock when called with interrupts disabled.
375     * We allow cpu's that are not yet online though, as no one else can
376     * send smp call function interrupt to this cpu and as such deadlocks
377     * can't happen.
378     */
379    WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
380             && !oops_in_progress);
381
382    /* So, what's a CPU they want? Ignoring this one. */
383    cpu = cpumask_first_and(mask, cpu_online_mask);
384    if (cpu == this_cpu)
385        cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
386
387    /* No online cpus? We're done. */
388    if (cpu >= nr_cpu_ids)
389        return;
390
391    /* Do we have another CPU which isn't us? */
392    next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
393    if (next_cpu == this_cpu)
394        next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
395
396    /* Fastpath: do that cpu by itself. */
397    if (next_cpu >= nr_cpu_ids) {
398        smp_call_function_single(cpu, func, info, wait);
399        return;
400    }
401
402    data = &__get_cpu_var(cfd_data);
403    csd_lock(&data->csd);
404
405    data->csd.func = func;
406    data->csd.info = info;
407    cpumask_and(data->cpumask, mask, cpu_online_mask);
408    cpumask_clear_cpu(this_cpu, data->cpumask);
409    atomic_set(&data->refs, cpumask_weight(data->cpumask));
410
411    spin_lock_irqsave(&call_function.lock, flags);
412    /*
413     * Place entry at the _HEAD_ of the list, so that any cpu still
414     * observing the entry in generic_smp_call_function_interrupt()
415     * will not miss any other list entries:
416     */
417    list_add_rcu(&data->csd.list, &call_function.queue);
418    spin_unlock_irqrestore(&call_function.lock, flags);
419
420    /*
421     * Make the list addition visible before sending the ipi.
422     * (IPIs must obey or appear to obey normal Linux cache
423     * coherency rules -- see comment in generic_exec_single).
424     */
425    smp_mb();
426
427    /* Send a message to all CPUs in the map */
428    arch_send_call_function_ipi_mask(data->cpumask);
429
430    /* Optionally wait for the CPUs to complete */
431    if (wait)
432        csd_lock_wait(&data->csd);
433}
434EXPORT_SYMBOL(smp_call_function_many);
435
436/**
437 * smp_call_function(): Run a function on all other CPUs.
438 * @func: The function to run. This must be fast and non-blocking.
439 * @info: An arbitrary pointer to pass to the function.
440 * @wait: If true, wait (atomically) until function has completed
441 * on other CPUs.
442 *
443 * Returns 0.
444 *
445 * If @wait is true, then returns once @func has returned; otherwise
446 * it returns just before the target cpu calls @func. In case of allocation
447 * failure, @wait will be implicitly turned on.
448 *
449 * You must not call this function with disabled interrupts or from a
450 * hardware interrupt handler or from a bottom half handler.
451 */
452int smp_call_function(void (*func)(void *), void *info, int wait)
453{
454    preempt_disable();
455    smp_call_function_many(cpu_online_mask, func, info, wait);
456    preempt_enable();
457
458    return 0;
459}
460EXPORT_SYMBOL(smp_call_function);
461
462void ipi_call_lock(void)
463{
464    spin_lock(&call_function.lock);
465}
466
467void ipi_call_unlock(void)
468{
469    spin_unlock(&call_function.lock);
470}
471
472void ipi_call_lock_irq(void)
473{
474    spin_lock_irq(&call_function.lock);
475}
476
477void ipi_call_unlock_irq(void)
478{
479    spin_unlock_irq(&call_function.lock);
480}
481

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