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
18#ifdef CONFIG_SMP
19/* Serializes the updates to cpu_online_mask, cpu_present_mask */
20static DEFINE_MUTEX(cpu_add_remove_lock);
21
22static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
23
24/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
25 * Should always be manipulated under cpu_add_remove_lock
26 */
27static int cpu_hotplug_disabled;
28
29static struct {
30    struct task_struct *active_writer;
31    struct mutex lock; /* Synchronizes accesses to refcount, */
32    /*
33     * Also blocks the new readers during
34     * an ongoing cpu hotplug operation.
35     */
36    int refcount;
37} cpu_hotplug = {
38    .active_writer = NULL,
39    .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
40    .refcount = 0,
41};
42
43#ifdef CONFIG_HOTPLUG_CPU
44
45void get_online_cpus(void)
46{
47    might_sleep();
48    if (cpu_hotplug.active_writer == current)
49        return;
50    mutex_lock(&cpu_hotplug.lock);
51    cpu_hotplug.refcount++;
52    mutex_unlock(&cpu_hotplug.lock);
53
54}
55EXPORT_SYMBOL_GPL(get_online_cpus);
56
57void put_online_cpus(void)
58{
59    if (cpu_hotplug.active_writer == current)
60        return;
61    mutex_lock(&cpu_hotplug.lock);
62    if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
63        wake_up_process(cpu_hotplug.active_writer);
64    mutex_unlock(&cpu_hotplug.lock);
65
66}
67EXPORT_SYMBOL_GPL(put_online_cpus);
68
69#endif /* CONFIG_HOTPLUG_CPU */
70
71/*
72 * The following two API's must be used when attempting
73 * to serialize the updates to cpu_online_mask, cpu_present_mask.
74 */
75void cpu_maps_update_begin(void)
76{
77    mutex_lock(&cpu_add_remove_lock);
78}
79
80void cpu_maps_update_done(void)
81{
82    mutex_unlock(&cpu_add_remove_lock);
83}
84
85/*
86 * This ensures that the hotplug operation can begin only when the
87 * refcount goes to zero.
88 *
89 * Note that during a cpu-hotplug operation, the new readers, if any,
90 * will be blocked by the cpu_hotplug.lock
91 *
92 * Since cpu_hotplug_begin() is always called after invoking
93 * cpu_maps_update_begin(), we can be sure that only one writer is active.
94 *
95 * Note that theoretically, there is a possibility of a livelock:
96 * - Refcount goes to zero, last reader wakes up the sleeping
97 * writer.
98 * - Last reader unlocks the cpu_hotplug.lock.
99 * - A new reader arrives at this moment, bumps up the refcount.
100 * - The writer acquires the cpu_hotplug.lock finds the refcount
101 * non zero and goes to sleep again.
102 *
103 * However, this is very difficult to achieve in practice since
104 * get_online_cpus() not an api which is called all that often.
105 *
106 */
107static void cpu_hotplug_begin(void)
108{
109    cpu_hotplug.active_writer = current;
110
111    for (;;) {
112        mutex_lock(&cpu_hotplug.lock);
113        if (likely(!cpu_hotplug.refcount))
114            break;
115        __set_current_state(TASK_UNINTERRUPTIBLE);
116        mutex_unlock(&cpu_hotplug.lock);
117        schedule();
118    }
119}
120
121static void cpu_hotplug_done(void)
122{
123    cpu_hotplug.active_writer = NULL;
124    mutex_unlock(&cpu_hotplug.lock);
125}
126/* Need to know about CPUs going up/down? */
127int __ref register_cpu_notifier(struct notifier_block *nb)
128{
129    int ret;
130    cpu_maps_update_begin();
131    ret = raw_notifier_chain_register(&cpu_chain, nb);
132    cpu_maps_update_done();
133    return ret;
134}
135
136#ifdef CONFIG_HOTPLUG_CPU
137
138EXPORT_SYMBOL(register_cpu_notifier);
139
140void __ref unregister_cpu_notifier(struct notifier_block *nb)
141{
142    cpu_maps_update_begin();
143    raw_notifier_chain_unregister(&cpu_chain, nb);
144    cpu_maps_update_done();
145}
146EXPORT_SYMBOL(unregister_cpu_notifier);
147
148static inline void check_for_tasks(int cpu)
149{
150    struct task_struct *p;
151
152    write_lock_irq(&tasklist_lock);
153    for_each_process(p) {
154        if (task_cpu(p) == cpu &&
155            (!cputime_eq(p->utime, cputime_zero) ||
156             !cputime_eq(p->stime, cputime_zero)))
157            printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
158                (state = %ld, flags = %x) \n",
159                 p->comm, task_pid_nr(p), cpu,
160                 p->state, p->flags);
161    }
162    write_unlock_irq(&tasklist_lock);
163}
164
165struct take_cpu_down_param {
166    unsigned long mod;
167    void *hcpu;
168};
169
170/* Take this CPU down. */
171static int __ref take_cpu_down(void *_param)
172{
173    struct take_cpu_down_param *param = _param;
174    int err;
175
176    /* Ensure this CPU doesn't handle any more interrupts. */
177    err = __cpu_disable();
178    if (err < 0)
179        return err;
180
181    raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
182                param->hcpu);
183
184    /* Force idle task to run as soon as we yield: it should
185       immediately notice cpu is offline and die quickly. */
186    sched_idle_next();
187    return 0;
188}
189
190/* Requires cpu_add_remove_lock to be held */
191static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
192{
193    int err, nr_calls = 0;
194    cpumask_var_t old_allowed;
195    void *hcpu = (void *)(long)cpu;
196    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
197    struct take_cpu_down_param tcd_param = {
198        .mod = mod,
199        .hcpu = hcpu,
200    };
201
202    if (num_online_cpus() == 1)
203        return -EBUSY;
204
205    if (!cpu_online(cpu))
206        return -EINVAL;
207
208    if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
209        return -ENOMEM;
210
211    cpu_hotplug_begin();
212    err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
213                    hcpu, -1, &nr_calls);
214    if (err == NOTIFY_BAD) {
215        set_cpu_active(cpu, true);
216
217        nr_calls--;
218        __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
219                      hcpu, nr_calls, NULL);
220        printk("%s: attempt to take down CPU %u failed\n",
221                __func__, cpu);
222        err = -EINVAL;
223        goto out_release;
224    }
225
226    /* Ensure that we are not runnable on dying cpu */
227    cpumask_copy(old_allowed, &current->cpus_allowed);
228    set_cpus_allowed_ptr(current, cpu_active_mask);
229
230    err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
231    if (err) {
232        set_cpu_active(cpu, true);
233        /* CPU didn't die: tell everyone. Can't complain. */
234        if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
235                        hcpu) == NOTIFY_BAD)
236            BUG();
237
238        goto out_allowed;
239    }
240    BUG_ON(cpu_online(cpu));
241
242    /* Wait for it to sleep (leaving idle task). */
243    while (!idle_cpu(cpu))
244        yield();
245
246    /* This actually kills the CPU. */
247    __cpu_die(cpu);
248
249    /* CPU is completely dead: tell everyone. Too late to complain. */
250    if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
251                    hcpu) == NOTIFY_BAD)
252        BUG();
253
254    check_for_tasks(cpu);
255
256out_allowed:
257    set_cpus_allowed_ptr(current, old_allowed);
258out_release:
259    cpu_hotplug_done();
260    if (!err) {
261        if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
262                        hcpu) == NOTIFY_BAD)
263            BUG();
264    }
265    free_cpumask_var(old_allowed);
266    return err;
267}
268
269int __ref cpu_down(unsigned int cpu)
270{
271    int err;
272
273    err = stop_machine_create();
274    if (err)
275        return err;
276    cpu_maps_update_begin();
277
278    if (cpu_hotplug_disabled) {
279        err = -EBUSY;
280        goto out;
281    }
282
283    set_cpu_active(cpu, false);
284
285    /*
286     * Make sure the all cpus did the reschedule and are not
287     * using stale version of the cpu_active_mask.
288     * This is not strictly necessary becuase stop_machine()
289     * that we run down the line already provides the required
290     * synchronization. But it's really a side effect and we do not
291     * want to depend on the innards of the stop_machine here.
292     */
293    synchronize_sched();
294
295    err = _cpu_down(cpu, 0);
296
297out:
298    cpu_maps_update_done();
299    stop_machine_destroy();
300    return err;
301}
302EXPORT_SYMBOL(cpu_down);
303#endif /*CONFIG_HOTPLUG_CPU*/
304
305/* Requires cpu_add_remove_lock to be held */
306static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
307{
308    int ret, nr_calls = 0;
309    void *hcpu = (void *)(long)cpu;
310    unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
311
312    if (cpu_online(cpu) || !cpu_present(cpu))
313        return -EINVAL;
314
315    cpu_hotplug_begin();
316    ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
317                            -1, &nr_calls);
318    if (ret == NOTIFY_BAD) {
319        nr_calls--;
320        printk("%s: attempt to bring up CPU %u failed\n",
321                __func__, cpu);
322        ret = -EINVAL;
323        goto out_notify;
324    }
325
326    /* Arch-specific enabling code. */
327    ret = __cpu_up(cpu);
328    if (ret != 0)
329        goto out_notify;
330    BUG_ON(!cpu_online(cpu));
331
332    set_cpu_active(cpu, true);
333
334    /* Now call notifier in preparation. */
335    raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
336
337out_notify:
338    if (ret != 0)
339        __raw_notifier_call_chain(&cpu_chain,
340                CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
341    cpu_hotplug_done();
342
343    return ret;
344}
345
346int __cpuinit cpu_up(unsigned int cpu)
347{
348    int err = 0;
349    if (!cpu_possible(cpu)) {
350        printk(KERN_ERR "can't online cpu %d because it is not "
351            "configured as may-hotadd at boot time\n", cpu);
352#if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
353        printk(KERN_ERR "please check additional_cpus= boot "
354                "parameter\n");
355#endif
356        return -EINVAL;
357    }
358
359    cpu_maps_update_begin();
360
361    if (cpu_hotplug_disabled) {
362        err = -EBUSY;
363        goto out;
364    }
365
366    err = _cpu_up(cpu, 0);
367
368out:
369    cpu_maps_update_done();
370    return err;
371}
372
373#ifdef CONFIG_PM_SLEEP_SMP
374static cpumask_var_t frozen_cpus;
375
376int disable_nonboot_cpus(void)
377{
378    int cpu, first_cpu, error;
379
380    error = stop_machine_create();
381    if (error)
382        return error;
383    cpu_maps_update_begin();
384    first_cpu = cpumask_first(cpu_online_mask);
385    /* We take down all of the non-boot CPUs in one shot to avoid races
386     * with the userspace trying to use the CPU hotplug at the same time
387     */
388    cpumask_clear(frozen_cpus);
389
390    for_each_online_cpu(cpu) {
391        if (cpu == first_cpu)
392            continue;
393        set_cpu_active(cpu, false);
394    }
395
396    synchronize_sched();
397
398    printk("Disabling non-boot CPUs ...\n");
399    for_each_online_cpu(cpu) {
400        if (cpu == first_cpu)
401            continue;
402        error = _cpu_down(cpu, 1);
403        if (!error)
404            cpumask_set_cpu(cpu, frozen_cpus);
405        else {
406            printk(KERN_ERR "Error taking CPU%d down: %d\n",
407                cpu, error);
408            break;
409        }
410    }
411
412    if (!error) {
413        BUG_ON(num_online_cpus() > 1);
414        /* Make sure the CPUs won't be enabled by someone else */
415        cpu_hotplug_disabled = 1;
416    } else {
417        printk(KERN_ERR "Non-boot CPUs are not disabled\n");
418    }
419    cpu_maps_update_done();
420    stop_machine_destroy();
421    return error;
422}
423
424void __weak arch_enable_nonboot_cpus_begin(void)
425{
426}
427
428void __weak arch_enable_nonboot_cpus_end(void)
429{
430}
431
432void __ref enable_nonboot_cpus(void)
433{
434    int cpu, error;
435
436    /* Allow everyone to use the CPU hotplug again */
437    cpu_maps_update_begin();
438    cpu_hotplug_disabled = 0;
439    if (cpumask_empty(frozen_cpus))
440        goto out;
441
442    printk("Enabling non-boot CPUs ...\n");
443
444    arch_enable_nonboot_cpus_begin();
445
446    for_each_cpu(cpu, frozen_cpus) {
447        error = _cpu_up(cpu, 1);
448        if (!error) {
449            printk("CPU%d is up\n", cpu);
450            continue;
451        }
452        printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
453    }
454
455    arch_enable_nonboot_cpus_end();
456
457    cpumask_clear(frozen_cpus);
458out:
459    cpu_maps_update_done();
460}
461
462static int alloc_frozen_cpus(void)
463{
464    if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
465        return -ENOMEM;
466    return 0;
467}
468core_initcall(alloc_frozen_cpus);
469#endif /* CONFIG_PM_SLEEP_SMP */
470
471/**
472 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
473 * @cpu: cpu that just started
474 *
475 * This function calls the cpu_chain notifiers with CPU_STARTING.
476 * It must be called by the arch code on the new cpu, before the new cpu
477 * enables interrupts and before the "boot" cpu returns from __cpu_up().
478 */
479void __cpuinit notify_cpu_starting(unsigned int cpu)
480{
481    unsigned long val = CPU_STARTING;
482
483#ifdef CONFIG_PM_SLEEP_SMP
484    if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
485        val = CPU_STARTING_FROZEN;
486#endif /* CONFIG_PM_SLEEP_SMP */
487    raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
488}
489
490#endif /* CONFIG_SMP */
491
492/*
493 * cpu_bit_bitmap[] is a special, "compressed" data structure that
494 * represents all NR_CPUS bits binary values of 1<<nr.
495 *
496 * It is used by cpumask_of() to get a constant address to a CPU
497 * mask value that has a single bit set only.
498 */
499
500/* cpu_bit_bitmap[0] is empty - so we can back into it */
501#define MASK_DECLARE_1(x) [x+1][0] = 1UL << (x)
502#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
503#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
504#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
505
506const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
507
508    MASK_DECLARE_8(0), MASK_DECLARE_8(8),
509    MASK_DECLARE_8(16), MASK_DECLARE_8(24),
510#if BITS_PER_LONG > 32
511    MASK_DECLARE_8(32), MASK_DECLARE_8(40),
512    MASK_DECLARE_8(48), MASK_DECLARE_8(56),
513#endif
514};
515EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
516
517const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
518EXPORT_SYMBOL(cpu_all_bits);
519
520#ifdef CONFIG_INIT_ALL_POSSIBLE
521static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
522    = CPU_BITS_ALL;
523#else
524static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
525#endif
526const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
527EXPORT_SYMBOL(cpu_possible_mask);
528
529static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
530const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
531EXPORT_SYMBOL(cpu_online_mask);
532
533static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
534const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
535EXPORT_SYMBOL(cpu_present_mask);
536
537static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
538const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
539EXPORT_SYMBOL(cpu_active_mask);
540
541void set_cpu_possible(unsigned int cpu, bool possible)
542{
543    if (possible)
544        cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
545    else
546        cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
547}
548
549void set_cpu_present(unsigned int cpu, bool present)
550{
551    if (present)
552        cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
553    else
554        cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
555}
556
557void set_cpu_online(unsigned int cpu, bool online)
558{
559    if (online)
560        cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
561    else
562        cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
563}
564
565void set_cpu_active(unsigned int cpu, bool active)
566{
567    if (active)
568        cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
569    else
570        cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
571}
572
573void init_cpu_present(const struct cpumask *src)
574{
575    cpumask_copy(to_cpumask(cpu_present_bits), src);
576}
577
578void init_cpu_possible(const struct cpumask *src)
579{
580    cpumask_copy(to_cpumask(cpu_possible_bits), src);
581}
582
583void init_cpu_online(const struct cpumask *src)
584{
585    cpumask_copy(to_cpumask(cpu_online_bits), src);
586}
587

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