projects/linux·blob v7.1-rc6 · refs

322 lines · 7.2 KiB

1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Common SMP CPU bringup/teardown functions
4 */
5#include <linux/cpu.h>
6#include <linux/err.h>
7#include <linux/smp.h>
8#include <linux/delay.h>
9#include <linux/init.h>
10#include <linux/list.h>
11#include <linux/slab.h>
12#include <linux/sched.h>
13#include <linux/sched/task.h>
14#include <linux/export.h>
15#include <linux/percpu.h>
16#include <linux/kthread.h>
17#include <linux/smpboot.h>
18
19#include "smpboot.h"
20
21#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
22/*
23 * For the hotplug case we keep the task structs around and reuse
24 * them.
25 */
26static DEFINE_PER_CPU(struct task_struct *, idle_threads);
27
28struct task_struct *idle_thread_get(unsigned int cpu)
29{
30 struct task_struct *tsk = per_cpu(idle_threads, cpu);
31
32 if (!tsk)
33 return ERR_PTR(-ENOMEM);
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 __always_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
77static LIST_HEAD(hotplug_threads);
78static DEFINE_MUTEX(smpboot_threads_lock);
79
80struct smpboot_thread_data {
81 unsigned int cpu;
82 unsigned int status;
83 struct smp_hotplug_thread *ht;
84};
85
86enum {
87 HP_THREAD_NONE = 0,
88 HP_THREAD_ACTIVE,
89 HP_THREAD_PARKED,
90};
91
92/**
93 * smpboot_thread_fn - percpu hotplug thread loop function
94 * @data: thread data pointer
95 *
96 * Checks for thread stop and park conditions. Calls the necessary
97 * setup, cleanup, park and unpark functions for the registered
98 * thread.
99 *
100 * Returns 1 when the thread should exit, 0 otherwise.
101 */
102static int smpboot_thread_fn(void *data)
103{
104 struct smpboot_thread_data *td = data;
105 struct smp_hotplug_thread *ht = td->ht;
106
107 while (1) {
108 set_current_state(TASK_INTERRUPTIBLE);
109 preempt_disable();
110 if (kthread_should_stop()) {
111 __set_current_state(TASK_RUNNING);
112 preempt_enable();
113 /* cleanup must mirror setup */
114 if (ht->cleanup && td->status != HP_THREAD_NONE)
115 ht->cleanup(td->cpu, cpu_online(td->cpu));
116 kfree(td);
117 return 0;
118 }
119
120 if (kthread_should_park()) {
121 __set_current_state(TASK_RUNNING);
122 preempt_enable();
123 if (ht->park && td->status == HP_THREAD_ACTIVE) {
124 BUG_ON(td->cpu != smp_processor_id());
125 ht->park(td->cpu);
126 td->status = HP_THREAD_PARKED;
127 }
128 kthread_parkme();
129 /* We might have been woken for stop */
130 continue;
131 }
132
133 BUG_ON(td->cpu != smp_processor_id());
134
135 /* Check for state change setup */
136 switch (td->status) {
137 case HP_THREAD_NONE:
138 __set_current_state(TASK_RUNNING);
139 preempt_enable();
140 if (ht->setup)
141 ht->setup(td->cpu);
142 td->status = HP_THREAD_ACTIVE;
143 continue;
144
145 case HP_THREAD_PARKED:
146 __set_current_state(TASK_RUNNING);
147 preempt_enable();
148 if (ht->unpark)
149 ht->unpark(td->cpu);
150 td->status = HP_THREAD_ACTIVE;
151 continue;
152 }
153
154 if (!ht->thread_should_run(td->cpu)) {
155 preempt_enable_no_resched();
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 kthread_set_per_cpu(tsk, cpu);
187 /*
188 * Park the thread so that it could start right on the CPU
189 * when it is available.
190 */
191 kthread_park(tsk);
192 get_task_struct(tsk);
193 *per_cpu_ptr(ht->store, cpu) = tsk;
194 if (ht->create) {
195 /*
196 * Make sure that the task has actually scheduled out
197 * into park position, before calling the create
198 * callback. At least the migration thread callback
199 * requires that the task is off the runqueue.
200 */
201 if (!wait_task_inactive(tsk, TASK_PARKED))
202 WARN_ON(1);
203 else
204 ht->create(cpu);
205 }
206 return 0;
207}
208
209int smpboot_create_threads(unsigned int cpu)
210{
211 struct smp_hotplug_thread *cur;
212 int ret = 0;
213
214 mutex_lock(&smpboot_threads_lock);
215 list_for_each_entry(cur, &hotplug_threads, list) {
216 ret = __smpboot_create_thread(cur, cpu);
217 if (ret)
218 break;
219 }
220 mutex_unlock(&smpboot_threads_lock);
221 return ret;
222}
223
224static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
225{
226 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
227
228 if (!ht->selfparking)
229 kthread_unpark(tsk);
230}
231
232int smpboot_unpark_threads(unsigned int cpu)
233{
234 struct smp_hotplug_thread *cur;
235
236 mutex_lock(&smpboot_threads_lock);
237 list_for_each_entry(cur, &hotplug_threads, list)
238 smpboot_unpark_thread(cur, cpu);
239 mutex_unlock(&smpboot_threads_lock);
240 return 0;
241}
242
243static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
244{
245 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
246
247 if (tsk && !ht->selfparking)
248 kthread_park(tsk);
249}
250
251int smpboot_park_threads(unsigned int cpu)
252{
253 struct smp_hotplug_thread *cur;
254
255 mutex_lock(&smpboot_threads_lock);
256 list_for_each_entry_reverse(cur, &hotplug_threads, list)
257 smpboot_park_thread(cur, cpu);
258 mutex_unlock(&smpboot_threads_lock);
259 return 0;
260}
261
262static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
263{
264 unsigned int cpu;
265
266 /* We need to destroy also the parked threads of offline cpus */
267 for_each_possible_cpu(cpu) {
268 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
269
270 if (tsk) {
271 kthread_stop_put(tsk);
272 *per_cpu_ptr(ht->store, cpu) = NULL;
273 }
274 }
275}
276
277/**
278 * smpboot_register_percpu_thread - Register a per_cpu thread related
279 * to hotplug
280 * @plug_thread: Hotplug thread descriptor
281 *
282 * Creates and starts the threads on all online cpus.
283 */
284int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
285{
286 unsigned int cpu;
287 int ret = 0;
288
289 cpus_read_lock();
290 mutex_lock(&smpboot_threads_lock);
291 for_each_online_cpu(cpu) {
292 ret = __smpboot_create_thread(plug_thread, cpu);
293 if (ret) {
294 smpboot_destroy_threads(plug_thread);
295 goto out;
296 }
297 smpboot_unpark_thread(plug_thread, cpu);
298 }
299 list_add(&plug_thread->list, &hotplug_threads);
300out:
301 mutex_unlock(&smpboot_threads_lock);
302 cpus_read_unlock();
303 return ret;
304}
305EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
306
307/**
308 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
309 * @plug_thread: Hotplug thread descriptor
310 *
311 * Stops all threads on all possible cpus.
312 */
313void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
314{
315 cpus_read_lock();
316 mutex_lock(&smpboot_threads_lock);
317 list_del(&plug_thread->list);
318 smpboot_destroy_threads(plug_thread);
319 mutex_unlock(&smpboot_threads_lock);
320 cpus_read_unlock();
321}
322EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);