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

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