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 /* #esle #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}
163
164EXPORT_SYMBOL(register_cpu_notifier);
165
166void __ref unregister_cpu_notifier(struct notifier_block *nb)
167{
168    cpu_maps_update_begin();
169    raw_notifier_chain_unregister(&cpu_chain, nb);
170    cpu_maps_update_done();
171}
172EXPORT_SYMBOL(unregister_cpu_notifier);
173
174static inline void check_for_tasks(int cpu)
175{
176    struct task_struct *p;
177
178    write_lock_irq(&tasklist_lock);
179    for_each_process(p) {
180        if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
181            (!cputime_eq(p->utime, cputime_zero) ||
182             !cputime_eq(p->stime, cputime_zero)))
183            printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
184                "(state = %ld, flags = %x)\n",
185                p->comm, task_pid_nr(p), cpu,
186                p->state, p->flags);
187    }
188    write_unlock_irq(&tasklist_lock);
189}
190
191struct take_cpu_down_param {
192    unsigned long mod;
193    void *hcpu;
194};
195
196/* Take this CPU down. */
197static int __ref take_cpu_down(void *_param)
198{
199    struct take_cpu_down_param *param = _param;
200    int err;
201
202    /* Ensure this CPU doesn't handle any more interrupts. */
203    err = __cpu_disable();
204    if (err < 0)
205        return err;
206
207    cpu_notify(CPU_DYING | param->mod, param->hcpu);
208
209    return 0;
210}
211
212/* Requires cpu_add_remove_lock to be held */
213static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
214{
215    int err, nr_calls = 0;
216    void *hcpu = (void *)(long)cpu;
217    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
218    struct take_cpu_down_param tcd_param = {
219        .mod = mod,
220        .hcpu = hcpu,
221    };
222
223    if (num_online_cpus() == 1)
224        return -EBUSY;
225
226    if (!cpu_online(cpu))
227        return -EINVAL;
228
229    cpu_hotplug_begin();
230    err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
231    if (err) {
232        nr_calls--;
233        __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
234        printk("%s: attempt to take down CPU %u failed\n",
235                __func__, cpu);
236        goto out_release;
237    }
238
239    err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
240    if (err) {
241        /* CPU didn't die: tell everyone. Can't complain. */
242        cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
243
244        goto out_release;
245    }
246    BUG_ON(cpu_online(cpu));
247
248    /*
249     * The migration_call() CPU_DYING callback will have removed all
250     * runnable tasks from the cpu, there's only the idle task left now
251     * that the migration thread is done doing the stop_machine thing.
252     *
253     * Wait for the stop thread to go away.
254     */
255    while (!idle_cpu(cpu))
256        cpu_relax();
257
258    /* This actually kills the CPU. */
259    __cpu_die(cpu);
260
261    /* CPU is completely dead: tell everyone. Too late to complain. */
262    cpu_notify_nofail(CPU_DEAD | mod, hcpu);
263
264    check_for_tasks(cpu);
265
266out_release:
267    cpu_hotplug_done();
268    if (!err)
269        cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
270    return err;
271}
272
273int __ref cpu_down(unsigned int cpu)
274{
275    int err;
276
277    cpu_maps_update_begin();
278
279    if (cpu_hotplug_disabled) {
280        err = -EBUSY;
281        goto out;
282    }
283
284    err = _cpu_down(cpu, 0);
285
286out:
287    cpu_maps_update_done();
288    return err;
289}
290EXPORT_SYMBOL(cpu_down);
291#endif /*CONFIG_HOTPLUG_CPU*/
292
293/* Requires cpu_add_remove_lock to be held */
294static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
295{
296    int ret, nr_calls = 0;
297    void *hcpu = (void *)(long)cpu;
298    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
299
300    if (cpu_online(cpu) || !cpu_present(cpu))
301        return -EINVAL;
302
303    cpu_hotplug_begin();
304    ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
305    if (ret) {
306        nr_calls--;
307        printk("%s: attempt to bring up CPU %u failed\n",
308                __func__, cpu);
309        goto out_notify;
310    }
311
312    /* Arch-specific enabling code. */
313    ret = __cpu_up(cpu);
314    if (ret != 0)
315        goto out_notify;
316    BUG_ON(!cpu_online(cpu));
317
318    /* Now call notifier in preparation. */
319    cpu_notify(CPU_ONLINE | mod, hcpu);
320
321out_notify:
322    if (ret != 0)
323        __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
324    cpu_hotplug_done();
325
326    return ret;
327}
328
329int __cpuinit cpu_up(unsigned int cpu)
330{
331    int err = 0;
332
333#ifdef CONFIG_MEMORY_HOTPLUG
334    int nid;
335    pg_data_t *pgdat;
336#endif
337
338    if (!cpu_possible(cpu)) {
339        printk(KERN_ERR "can't online cpu %d because it is not "
340            "configured as may-hotadd at boot time\n", cpu);
341#if defined(CONFIG_IA64)
342        printk(KERN_ERR "please check additional_cpus= boot "
343                "parameter\n");
344#endif
345        return -EINVAL;
346    }
347
348#ifdef CONFIG_MEMORY_HOTPLUG
349    nid = cpu_to_node(cpu);
350    if (!node_online(nid)) {
351        err = mem_online_node(nid);
352        if (err)
353            return err;
354    }
355
356    pgdat = NODE_DATA(nid);
357    if (!pgdat) {
358        printk(KERN_ERR
359            "Can't online cpu %d due to NULL pgdat\n", cpu);
360        return -ENOMEM;
361    }
362
363    if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
364        mutex_lock(&zonelists_mutex);
365        build_all_zonelists(NULL);
366        mutex_unlock(&zonelists_mutex);
367    }
368#endif
369
370    cpu_maps_update_begin();
371
372    if (cpu_hotplug_disabled) {
373        err = -EBUSY;
374        goto out;
375    }
376
377    err = _cpu_up(cpu, 0);
378
379out:
380    cpu_maps_update_done();
381    return err;
382}
383
384#ifdef CONFIG_PM_SLEEP_SMP
385static cpumask_var_t frozen_cpus;
386
387void __weak arch_disable_nonboot_cpus_begin(void)
388{
389}
390
391void __weak arch_disable_nonboot_cpus_end(void)
392{
393}
394
395int disable_nonboot_cpus(void)
396{
397    int cpu, first_cpu, error = 0;
398
399    cpu_maps_update_begin();
400    first_cpu = cpumask_first(cpu_online_mask);
401    /*
402     * We take down all of the non-boot CPUs in one shot to avoid races
403     * with the userspace trying to use the CPU hotplug at the same time
404     */
405    cpumask_clear(frozen_cpus);
406    arch_disable_nonboot_cpus_begin();
407
408    printk("Disabling non-boot CPUs ...\n");
409    for_each_online_cpu(cpu) {
410        if (cpu == first_cpu)
411            continue;
412        error = _cpu_down(cpu, 1);
413        if (!error)
414            cpumask_set_cpu(cpu, frozen_cpus);
415        else {
416            printk(KERN_ERR "Error taking CPU%d down: %d\n",
417                cpu, error);
418            break;
419        }
420    }
421
422    arch_disable_nonboot_cpus_end();
423
424    if (!error) {
425        BUG_ON(num_online_cpus() > 1);
426        /* Make sure the CPUs won't be enabled by someone else */
427        cpu_hotplug_disabled = 1;
428    } else {
429        printk(KERN_ERR "Non-boot CPUs are not disabled\n");
430    }
431    cpu_maps_update_done();
432    return error;
433}
434
435void __weak arch_enable_nonboot_cpus_begin(void)
436{
437}
438
439void __weak arch_enable_nonboot_cpus_end(void)
440{
441}
442
443void __ref enable_nonboot_cpus(void)
444{
445    int cpu, error;
446
447    /* Allow everyone to use the CPU hotplug again */
448    cpu_maps_update_begin();
449    cpu_hotplug_disabled = 0;
450    if (cpumask_empty(frozen_cpus))
451        goto out;
452
453    printk("Enabling non-boot CPUs ...\n");
454
455    arch_enable_nonboot_cpus_begin();
456
457    for_each_cpu(cpu, frozen_cpus) {
458        error = _cpu_up(cpu, 1);
459        if (!error) {
460            printk("CPU%d is up\n", cpu);
461            continue;
462        }
463        printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
464    }
465
466    arch_enable_nonboot_cpus_end();
467
468    cpumask_clear(frozen_cpus);
469out:
470    cpu_maps_update_done();
471}
472
473static int alloc_frozen_cpus(void)
474{
475    if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
476        return -ENOMEM;
477    return 0;
478}
479core_initcall(alloc_frozen_cpus);
480#endif /* CONFIG_PM_SLEEP_SMP */
481
482/**
483 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
484 * @cpu: cpu that just started
485 *
486 * This function calls the cpu_chain notifiers with CPU_STARTING.
487 * It must be called by the arch code on the new cpu, before the new cpu
488 * enables interrupts and before the "boot" cpu returns from __cpu_up().
489 */
490void __cpuinit notify_cpu_starting(unsigned int cpu)
491{
492    unsigned long val = CPU_STARTING;
493
494#ifdef CONFIG_PM_SLEEP_SMP
495    if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
496        val = CPU_STARTING_FROZEN;
497#endif /* CONFIG_PM_SLEEP_SMP */
498    cpu_notify(val, (void *)(long)cpu);
499}
500
501#endif /* CONFIG_SMP */
502
503/*
504 * cpu_bit_bitmap[] is a special, "compressed" data structure that
505 * represents all NR_CPUS bits binary values of 1<<nr.
506 *
507 * It is used by cpumask_of() to get a constant address to a CPU
508 * mask value that has a single bit set only.
509 */
510
511/* cpu_bit_bitmap[0] is empty - so we can back into it */
512#define MASK_DECLARE_1(x) [x+1][0] = 1UL << (x)
513#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
514#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
515#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
516
517const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
518
519    MASK_DECLARE_8(0), MASK_DECLARE_8(8),
520    MASK_DECLARE_8(16), MASK_DECLARE_8(24),
521#if BITS_PER_LONG > 32
522    MASK_DECLARE_8(32), MASK_DECLARE_8(40),
523    MASK_DECLARE_8(48), MASK_DECLARE_8(56),
524#endif
525};
526EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
527
528const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
529EXPORT_SYMBOL(cpu_all_bits);
530
531#ifdef CONFIG_INIT_ALL_POSSIBLE
532static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
533    = CPU_BITS_ALL;
534#else
535static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
536#endif
537const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
538EXPORT_SYMBOL(cpu_possible_mask);
539
540static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
541const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
542EXPORT_SYMBOL(cpu_online_mask);
543
544static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
545const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
546EXPORT_SYMBOL(cpu_present_mask);
547
548static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
549const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
550EXPORT_SYMBOL(cpu_active_mask);
551
552void set_cpu_possible(unsigned int cpu, bool possible)
553{
554    if (possible)
555        cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
556    else
557        cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
558}
559
560void set_cpu_present(unsigned int cpu, bool present)
561{
562    if (present)
563        cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
564    else
565        cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
566}
567
568void set_cpu_online(unsigned int cpu, bool online)
569{
570    if (online)
571        cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
572    else
573        cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
574}
575
576void set_cpu_active(unsigned int cpu, bool active)
577{
578    if (active)
579        cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
580    else
581        cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
582}
583
584void init_cpu_present(const struct cpumask *src)
585{
586    cpumask_copy(to_cpumask(cpu_present_bits), src);
587}
588
589void init_cpu_possible(const struct cpumask *src)
590{
591    cpumask_copy(to_cpumask(cpu_possible_bits), src);
592}
593
594void init_cpu_online(const struct cpumask *src)
595{
596    cpumask_copy(to_cpumask(cpu_online_bits), src);
597}
598

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