Root/kernel/cpu.c

1/* CPU control.
2 * (C) 2001, 2002, 2003, 2004 Rusty Russell
3 *
4 * This code is licenced under the GPL.
5 */
6#include <linux/proc_fs.h>
7#include <linux/smp.h>
8#include <linux/init.h>
9#include <linux/notifier.h>
10#include <linux/sched.h>
11#include <linux/unistd.h>
12#include <linux/cpu.h>
13#include <linux/module.h>
14#include <linux/kthread.h>
15#include <linux/stop_machine.h>
16#include <linux/mutex.h>
17#include <linux/gfp.h>
18
19#ifdef CONFIG_SMP
20/* Serializes the updates to cpu_online_mask, cpu_present_mask */
21static DEFINE_MUTEX(cpu_add_remove_lock);
22
23/*
24 * The following two API's must be used when attempting
25 * to serialize the updates to cpu_online_mask, cpu_present_mask.
26 */
27void cpu_maps_update_begin(void)
28{
29    mutex_lock(&cpu_add_remove_lock);
30}
31
32void cpu_maps_update_done(void)
33{
34    mutex_unlock(&cpu_add_remove_lock);
35}
36
37static RAW_NOTIFIER_HEAD(cpu_chain);
38
39/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
40 * Should always be manipulated under cpu_add_remove_lock
41 */
42static int cpu_hotplug_disabled;
43
44#ifdef CONFIG_HOTPLUG_CPU
45
46static struct {
47    struct task_struct *active_writer;
48    struct mutex lock; /* Synchronizes accesses to refcount, */
49    /*
50     * Also blocks the new readers during
51     * an ongoing cpu hotplug operation.
52     */
53    int refcount;
54} cpu_hotplug = {
55    .active_writer = NULL,
56    .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
57    .refcount = 0,
58};
59
60void get_online_cpus(void)
61{
62    might_sleep();
63    if (cpu_hotplug.active_writer == current)
64        return;
65    mutex_lock(&cpu_hotplug.lock);
66    cpu_hotplug.refcount++;
67    mutex_unlock(&cpu_hotplug.lock);
68
69}
70EXPORT_SYMBOL_GPL(get_online_cpus);
71
72void put_online_cpus(void)
73{
74    if (cpu_hotplug.active_writer == current)
75        return;
76    mutex_lock(&cpu_hotplug.lock);
77    if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
78        wake_up_process(cpu_hotplug.active_writer);
79    mutex_unlock(&cpu_hotplug.lock);
80
81}
82EXPORT_SYMBOL_GPL(put_online_cpus);
83
84/*
85 * This ensures that the hotplug operation can begin only when the
86 * refcount goes to zero.
87 *
88 * Note that during a cpu-hotplug operation, the new readers, if any,
89 * will be blocked by the cpu_hotplug.lock
90 *
91 * Since cpu_hotplug_begin() is always called after invoking
92 * cpu_maps_update_begin(), we can be sure that only one writer is active.
93 *
94 * Note that theoretically, there is a possibility of a livelock:
95 * - Refcount goes to zero, last reader wakes up the sleeping
96 * writer.
97 * - Last reader unlocks the cpu_hotplug.lock.
98 * - A new reader arrives at this moment, bumps up the refcount.
99 * - The writer acquires the cpu_hotplug.lock finds the refcount
100 * non zero and goes to sleep again.
101 *
102 * However, this is very difficult to achieve in practice since
103 * get_online_cpus() not an api which is called all that often.
104 *
105 */
106static void cpu_hotplug_begin(void)
107{
108    cpu_hotplug.active_writer = current;
109
110    for (;;) {
111        mutex_lock(&cpu_hotplug.lock);
112        if (likely(!cpu_hotplug.refcount))
113            break;
114        __set_current_state(TASK_UNINTERRUPTIBLE);
115        mutex_unlock(&cpu_hotplug.lock);
116        schedule();
117    }
118}
119
120static void cpu_hotplug_done(void)
121{
122    cpu_hotplug.active_writer = NULL;
123    mutex_unlock(&cpu_hotplug.lock);
124}
125
126#else /* #if CONFIG_HOTPLUG_CPU */
127static void cpu_hotplug_begin(void) {}
128static void cpu_hotplug_done(void) {}
129#endif /* #else #if CONFIG_HOTPLUG_CPU */
130
131/* Need to know about CPUs going up/down? */
132int __ref register_cpu_notifier(struct notifier_block *nb)
133{
134    int ret;
135    cpu_maps_update_begin();
136    ret = raw_notifier_chain_register(&cpu_chain, nb);
137    cpu_maps_update_done();
138    return ret;
139}
140
141static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
142            int *nr_calls)
143{
144    int ret;
145
146    ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
147                    nr_calls);
148
149    return notifier_to_errno(ret);
150}
151
152static int cpu_notify(unsigned long val, void *v)
153{
154    return __cpu_notify(val, v, -1, NULL);
155}
156
157#ifdef CONFIG_HOTPLUG_CPU
158
159static void cpu_notify_nofail(unsigned long val, void *v)
160{
161    BUG_ON(cpu_notify(val, v));
162}
163EXPORT_SYMBOL(register_cpu_notifier);
164
165void __ref unregister_cpu_notifier(struct notifier_block *nb)
166{
167    cpu_maps_update_begin();
168    raw_notifier_chain_unregister(&cpu_chain, nb);
169    cpu_maps_update_done();
170}
171EXPORT_SYMBOL(unregister_cpu_notifier);
172
173static inline void check_for_tasks(int cpu)
174{
175    struct task_struct *p;
176
177    write_lock_irq(&tasklist_lock);
178    for_each_process(p) {
179        if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
180            (!cputime_eq(p->utime, cputime_zero) ||
181             !cputime_eq(p->stime, cputime_zero)))
182            printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
183                "(state = %ld, flags = %x)\n",
184                p->comm, task_pid_nr(p), cpu,
185                p->state, p->flags);
186    }
187    write_unlock_irq(&tasklist_lock);
188}
189
190struct take_cpu_down_param {
191    unsigned long mod;
192    void *hcpu;
193};
194
195/* Take this CPU down. */
196static int __ref take_cpu_down(void *_param)
197{
198    struct take_cpu_down_param *param = _param;
199    int err;
200
201    /* Ensure this CPU doesn't handle any more interrupts. */
202    err = __cpu_disable();
203    if (err < 0)
204        return err;
205
206    cpu_notify(CPU_DYING | param->mod, param->hcpu);
207    return 0;
208}
209
210/* Requires cpu_add_remove_lock to be held */
211static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
212{
213    int err, nr_calls = 0;
214    void *hcpu = (void *)(long)cpu;
215    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
216    struct take_cpu_down_param tcd_param = {
217        .mod = mod,
218        .hcpu = hcpu,
219    };
220
221    if (num_online_cpus() == 1)
222        return -EBUSY;
223
224    if (!cpu_online(cpu))
225        return -EINVAL;
226
227    cpu_hotplug_begin();
228
229    err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
230    if (err) {
231        nr_calls--;
232        __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
233        printk("%s: attempt to take down CPU %u failed\n",
234                __func__, cpu);
235        goto out_release;
236    }
237
238    err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
239    if (err) {
240        /* CPU didn't die: tell everyone. Can't complain. */
241        cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
242
243        goto out_release;
244    }
245    BUG_ON(cpu_online(cpu));
246
247    /*
248     * The migration_call() CPU_DYING callback will have removed all
249     * runnable tasks from the cpu, there's only the idle task left now
250     * that the migration thread is done doing the stop_machine thing.
251     *
252     * Wait for the stop thread to go away.
253     */
254    while (!idle_cpu(cpu))
255        cpu_relax();
256
257    /* This actually kills the CPU. */
258    __cpu_die(cpu);
259
260    /* CPU is completely dead: tell everyone. Too late to complain. */
261    cpu_notify_nofail(CPU_DEAD | mod, hcpu);
262
263    check_for_tasks(cpu);
264
265out_release:
266    cpu_hotplug_done();
267    if (!err)
268        cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
269    return err;
270}
271
272int __ref cpu_down(unsigned int cpu)
273{
274    int err;
275
276    cpu_maps_update_begin();
277
278    if (cpu_hotplug_disabled) {
279        err = -EBUSY;
280        goto out;
281    }
282
283    err = _cpu_down(cpu, 0);
284
285out:
286    cpu_maps_update_done();
287    return err;
288}
289EXPORT_SYMBOL(cpu_down);
290#endif /*CONFIG_HOTPLUG_CPU*/
291
292/* Requires cpu_add_remove_lock to be held */
293static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
294{
295    int ret, nr_calls = 0;
296    void *hcpu = (void *)(long)cpu;
297    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
298
299    if (cpu_online(cpu) || !cpu_present(cpu))
300        return -EINVAL;
301
302    cpu_hotplug_begin();
303    ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
304    if (ret) {
305        nr_calls--;
306        printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
307                __func__, cpu);
308        goto out_notify;
309    }
310
311    /* Arch-specific enabling code. */
312    ret = __cpu_up(cpu);
313    if (ret != 0)
314        goto out_notify;
315    BUG_ON(!cpu_online(cpu));
316
317    /* Now call notifier in preparation. */
318    cpu_notify(CPU_ONLINE | mod, hcpu);
319
320out_notify:
321    if (ret != 0)
322        __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
323    cpu_hotplug_done();
324
325    return ret;
326}
327
328int __cpuinit cpu_up(unsigned int cpu)
329{
330    int err = 0;
331
332#ifdef CONFIG_MEMORY_HOTPLUG
333    int nid;
334    pg_data_t *pgdat;
335#endif
336
337    if (!cpu_possible(cpu)) {
338        printk(KERN_ERR "can't online cpu %d because it is not "
339            "configured as may-hotadd at boot time\n", cpu);
340#if defined(CONFIG_IA64)
341        printk(KERN_ERR "please check additional_cpus= boot "
342                "parameter\n");
343#endif
344        return -EINVAL;
345    }
346
347#ifdef CONFIG_MEMORY_HOTPLUG
348    nid = cpu_to_node(cpu);
349    if (!node_online(nid)) {
350        err = mem_online_node(nid);
351        if (err)
352            return err;
353    }
354
355    pgdat = NODE_DATA(nid);
356    if (!pgdat) {
357        printk(KERN_ERR
358            "Can't online cpu %d due to NULL pgdat\n", cpu);
359        return -ENOMEM;
360    }
361
362    if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
363        mutex_lock(&zonelists_mutex);
364        build_all_zonelists(NULL);
365        mutex_unlock(&zonelists_mutex);
366    }
367#endif
368
369    cpu_maps_update_begin();
370
371    if (cpu_hotplug_disabled) {
372        err = -EBUSY;
373        goto out;
374    }
375
376    err = _cpu_up(cpu, 0);
377
378out:
379    cpu_maps_update_done();
380    return err;
381}
382
383#ifdef CONFIG_PM_SLEEP_SMP
384static cpumask_var_t frozen_cpus;
385
386void __weak arch_disable_nonboot_cpus_begin(void)
387{
388}
389
390void __weak arch_disable_nonboot_cpus_end(void)
391{
392}
393
394int disable_nonboot_cpus(void)
395{
396    int cpu, first_cpu, error = 0;
397
398    cpu_maps_update_begin();
399    first_cpu = cpumask_first(cpu_online_mask);
400    /*
401     * We take down all of the non-boot CPUs in one shot to avoid races
402     * with the userspace trying to use the CPU hotplug at the same time
403     */
404    cpumask_clear(frozen_cpus);
405    arch_disable_nonboot_cpus_begin();
406
407    printk("Disabling non-boot CPUs ...\n");
408    for_each_online_cpu(cpu) {
409        if (cpu == first_cpu)
410            continue;
411        error = _cpu_down(cpu, 1);
412        if (!error)
413            cpumask_set_cpu(cpu, frozen_cpus);
414        else {
415            printk(KERN_ERR "Error taking CPU%d down: %d\n",
416                cpu, error);
417            break;
418        }
419    }
420
421    arch_disable_nonboot_cpus_end();
422
423    if (!error) {
424        BUG_ON(num_online_cpus() > 1);
425        /* Make sure the CPUs won't be enabled by someone else */
426        cpu_hotplug_disabled = 1;
427    } else {
428        printk(KERN_ERR "Non-boot CPUs are not disabled\n");
429    }
430    cpu_maps_update_done();
431    return error;
432}
433
434void __weak arch_enable_nonboot_cpus_begin(void)
435{
436}
437
438void __weak arch_enable_nonboot_cpus_end(void)
439{
440}
441
442void __ref enable_nonboot_cpus(void)
443{
444    int cpu, error;
445
446    /* Allow everyone to use the CPU hotplug again */
447    cpu_maps_update_begin();
448    cpu_hotplug_disabled = 0;
449    if (cpumask_empty(frozen_cpus))
450        goto out;
451
452    printk(KERN_INFO "Enabling non-boot CPUs ...\n");
453
454    arch_enable_nonboot_cpus_begin();
455
456    for_each_cpu(cpu, frozen_cpus) {
457        error = _cpu_up(cpu, 1);
458        if (!error) {
459            printk(KERN_INFO "CPU%d is up\n", cpu);
460            continue;
461        }
462        printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
463    }
464
465    arch_enable_nonboot_cpus_end();
466
467    cpumask_clear(frozen_cpus);
468out:
469    cpu_maps_update_done();
470}
471
472static int alloc_frozen_cpus(void)
473{
474    if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
475        return -ENOMEM;
476    return 0;
477}
478core_initcall(alloc_frozen_cpus);
479#endif /* CONFIG_PM_SLEEP_SMP */
480
481/**
482 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
483 * @cpu: cpu that just started
484 *
485 * This function calls the cpu_chain notifiers with CPU_STARTING.
486 * It must be called by the arch code on the new cpu, before the new cpu
487 * enables interrupts and before the "boot" cpu returns from __cpu_up().
488 */
489void __cpuinit notify_cpu_starting(unsigned int cpu)
490{
491    unsigned long val = CPU_STARTING;
492
493#ifdef CONFIG_PM_SLEEP_SMP
494    if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
495        val = CPU_STARTING_FROZEN;
496#endif /* CONFIG_PM_SLEEP_SMP */
497    cpu_notify(val, (void *)(long)cpu);
498}
499
500#endif /* CONFIG_SMP */
501
502/*
503 * cpu_bit_bitmap[] is a special, "compressed" data structure that
504 * represents all NR_CPUS bits binary values of 1<<nr.
505 *
506 * It is used by cpumask_of() to get a constant address to a CPU
507 * mask value that has a single bit set only.
508 */
509
510/* cpu_bit_bitmap[0] is empty - so we can back into it */
511#define MASK_DECLARE_1(x) [x+1][0] = (1UL << (x))
512#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
513#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
514#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
515
516const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
517
518    MASK_DECLARE_8(0), MASK_DECLARE_8(8),
519    MASK_DECLARE_8(16), MASK_DECLARE_8(24),
520#if BITS_PER_LONG > 32
521    MASK_DECLARE_8(32), MASK_DECLARE_8(40),
522    MASK_DECLARE_8(48), MASK_DECLARE_8(56),
523#endif
524};
525EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
526
527const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
528EXPORT_SYMBOL(cpu_all_bits);
529
530#ifdef CONFIG_INIT_ALL_POSSIBLE
531static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
532    = CPU_BITS_ALL;
533#else
534static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
535#endif
536const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
537EXPORT_SYMBOL(cpu_possible_mask);
538
539static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
540const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
541EXPORT_SYMBOL(cpu_online_mask);
542
543static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
544const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
545EXPORT_SYMBOL(cpu_present_mask);
546
547static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
548const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
549EXPORT_SYMBOL(cpu_active_mask);
550
551void set_cpu_possible(unsigned int cpu, bool possible)
552{
553    if (possible)
554        cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
555    else
556        cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
557}
558
559void set_cpu_present(unsigned int cpu, bool present)
560{
561    if (present)
562        cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
563    else
564        cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
565}
566
567void set_cpu_online(unsigned int cpu, bool online)
568{
569    if (online)
570        cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
571    else
572        cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
573}
574
575void set_cpu_active(unsigned int cpu, bool active)
576{
577    if (active)
578        cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
579    else
580        cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
581}
582
583void init_cpu_present(const struct cpumask *src)
584{
585    cpumask_copy(to_cpumask(cpu_present_bits), src);
586}
587
588void init_cpu_possible(const struct cpumask *src)
589{
590    cpumask_copy(to_cpumask(cpu_possible_bits), src);
591}
592
593void init_cpu_online(const struct cpumask *src)
594{
595    cpumask_copy(to_cpumask(cpu_online_bits), src);
596}
597

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