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

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