Root/kernel/smpboot.c

1/*
2 * Common SMP CPU bringup/teardown functions
3 */
4#include <linux/cpu.h>
5#include <linux/err.h>
6#include <linux/smp.h>
7#include <linux/init.h>
8#include <linux/list.h>
9#include <linux/slab.h>
10#include <linux/sched.h>
11#include <linux/export.h>
12#include <linux/percpu.h>
13#include <linux/kthread.h>
14#include <linux/smpboot.h>
15
16#include "smpboot.h"
17
18#ifdef CONFIG_SMP
19
20#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
21/*
22 * For the hotplug case we keep the task structs around and reuse
23 * them.
24 */
25static DEFINE_PER_CPU(struct task_struct *, idle_threads);
26
27struct task_struct *idle_thread_get(unsigned int cpu)
28{
29    struct task_struct *tsk = per_cpu(idle_threads, cpu);
30
31    if (!tsk)
32        return ERR_PTR(-ENOMEM);
33    init_idle(tsk, cpu);
34    return tsk;
35}
36
37void __init idle_thread_set_boot_cpu(void)
38{
39    per_cpu(idle_threads, smp_processor_id()) = current;
40}
41
42/**
43 * idle_init - Initialize the idle thread for a cpu
44 * @cpu: The cpu for which the idle thread should be initialized
45 *
46 * Creates the thread if it does not exist.
47 */
48static inline void idle_init(unsigned int cpu)
49{
50    struct task_struct *tsk = per_cpu(idle_threads, cpu);
51
52    if (!tsk) {
53        tsk = fork_idle(cpu);
54        if (IS_ERR(tsk))
55            pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
56        else
57            per_cpu(idle_threads, cpu) = tsk;
58    }
59}
60
61/**
62 * idle_threads_init - Initialize idle threads for all cpus
63 */
64void __init idle_threads_init(void)
65{
66    unsigned int cpu, boot_cpu;
67
68    boot_cpu = smp_processor_id();
69
70    for_each_possible_cpu(cpu) {
71        if (cpu != boot_cpu)
72            idle_init(cpu);
73    }
74}
75#endif
76
77#endif /* #ifdef CONFIG_SMP */
78
79static LIST_HEAD(hotplug_threads);
80static DEFINE_MUTEX(smpboot_threads_lock);
81
82struct smpboot_thread_data {
83    unsigned int cpu;
84    unsigned int status;
85    struct smp_hotplug_thread *ht;
86};
87
88enum {
89    HP_THREAD_NONE = 0,
90    HP_THREAD_ACTIVE,
91    HP_THREAD_PARKED,
92};
93
94/**
95 * smpboot_thread_fn - percpu hotplug thread loop function
96 * @data: thread data pointer
97 *
98 * Checks for thread stop and park conditions. Calls the necessary
99 * setup, cleanup, park and unpark functions for the registered
100 * thread.
101 *
102 * Returns 1 when the thread should exit, 0 otherwise.
103 */
104static int smpboot_thread_fn(void *data)
105{
106    struct smpboot_thread_data *td = data;
107    struct smp_hotplug_thread *ht = td->ht;
108
109    while (1) {
110        set_current_state(TASK_INTERRUPTIBLE);
111        preempt_disable();
112        if (kthread_should_stop()) {
113            set_current_state(TASK_RUNNING);
114            preempt_enable();
115            if (ht->cleanup)
116                ht->cleanup(td->cpu, cpu_online(td->cpu));
117            kfree(td);
118            return 0;
119        }
120
121        if (kthread_should_park()) {
122            __set_current_state(TASK_RUNNING);
123            preempt_enable();
124            if (ht->park && td->status == HP_THREAD_ACTIVE) {
125                BUG_ON(td->cpu != smp_processor_id());
126                ht->park(td->cpu);
127                td->status = HP_THREAD_PARKED;
128            }
129            kthread_parkme();
130            /* We might have been woken for stop */
131            continue;
132        }
133
134        BUG_ON(td->cpu != smp_processor_id());
135
136        /* Check for state change setup */
137        switch (td->status) {
138        case HP_THREAD_NONE:
139            preempt_enable();
140            if (ht->setup)
141                ht->setup(td->cpu);
142            td->status = HP_THREAD_ACTIVE;
143            preempt_disable();
144            break;
145        case HP_THREAD_PARKED:
146            preempt_enable();
147            if (ht->unpark)
148                ht->unpark(td->cpu);
149            td->status = HP_THREAD_ACTIVE;
150            preempt_disable();
151            break;
152        }
153
154        if (!ht->thread_should_run(td->cpu)) {
155            preempt_enable();
156            schedule();
157        } else {
158            set_current_state(TASK_RUNNING);
159            preempt_enable();
160            ht->thread_fn(td->cpu);
161        }
162    }
163}
164
165static int
166__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
167{
168    struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
169    struct smpboot_thread_data *td;
170
171    if (tsk)
172        return 0;
173
174    td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
175    if (!td)
176        return -ENOMEM;
177    td->cpu = cpu;
178    td->ht = ht;
179
180    tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
181                    ht->thread_comm);
182    if (IS_ERR(tsk)) {
183        kfree(td);
184        return PTR_ERR(tsk);
185    }
186    get_task_struct(tsk);
187    *per_cpu_ptr(ht->store, cpu) = tsk;
188    if (ht->create) {
189        /*
190         * Make sure that the task has actually scheduled out
191         * into park position, before calling the create
192         * callback. At least the migration thread callback
193         * requires that the task is off the runqueue.
194         */
195        if (!wait_task_inactive(tsk, TASK_PARKED))
196            WARN_ON(1);
197        else
198            ht->create(cpu);
199    }
200    return 0;
201}
202
203int smpboot_create_threads(unsigned int cpu)
204{
205    struct smp_hotplug_thread *cur;
206    int ret = 0;
207
208    mutex_lock(&smpboot_threads_lock);
209    list_for_each_entry(cur, &hotplug_threads, list) {
210        ret = __smpboot_create_thread(cur, cpu);
211        if (ret)
212            break;
213    }
214    mutex_unlock(&smpboot_threads_lock);
215    return ret;
216}
217
218static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
219{
220    struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
221
222    if (ht->pre_unpark)
223        ht->pre_unpark(cpu);
224    kthread_unpark(tsk);
225}
226
227void smpboot_unpark_threads(unsigned int cpu)
228{
229    struct smp_hotplug_thread *cur;
230
231    mutex_lock(&smpboot_threads_lock);
232    list_for_each_entry(cur, &hotplug_threads, list)
233        smpboot_unpark_thread(cur, cpu);
234    mutex_unlock(&smpboot_threads_lock);
235}
236
237static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
238{
239    struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
240
241    if (tsk && !ht->selfparking)
242        kthread_park(tsk);
243}
244
245void smpboot_park_threads(unsigned int cpu)
246{
247    struct smp_hotplug_thread *cur;
248
249    mutex_lock(&smpboot_threads_lock);
250    list_for_each_entry_reverse(cur, &hotplug_threads, list)
251        smpboot_park_thread(cur, cpu);
252    mutex_unlock(&smpboot_threads_lock);
253}
254
255static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
256{
257    unsigned int cpu;
258
259    /* We need to destroy also the parked threads of offline cpus */
260    for_each_possible_cpu(cpu) {
261        struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
262
263        if (tsk) {
264            kthread_stop(tsk);
265            put_task_struct(tsk);
266            *per_cpu_ptr(ht->store, cpu) = NULL;
267        }
268    }
269}
270
271/**
272 * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
273 * @plug_thread: Hotplug thread descriptor
274 *
275 * Creates and starts the threads on all online cpus.
276 */
277int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
278{
279    unsigned int cpu;
280    int ret = 0;
281
282    mutex_lock(&smpboot_threads_lock);
283    for_each_online_cpu(cpu) {
284        ret = __smpboot_create_thread(plug_thread, cpu);
285        if (ret) {
286            smpboot_destroy_threads(plug_thread);
287            goto out;
288        }
289        smpboot_unpark_thread(plug_thread, cpu);
290    }
291    list_add(&plug_thread->list, &hotplug_threads);
292out:
293    mutex_unlock(&smpboot_threads_lock);
294    return ret;
295}
296EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
297
298/**
299 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
300 * @plug_thread: Hotplug thread descriptor
301 *
302 * Stops all threads on all possible cpus.
303 */
304void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
305{
306    get_online_cpus();
307    mutex_lock(&smpboot_threads_lock);
308    list_del(&plug_thread->list);
309    smpboot_destroy_threads(plug_thread);
310    mutex_unlock(&smpboot_threads_lock);
311    put_online_cpus();
312}
313EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
314

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