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_SMP
22
23#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
24/*
25 * For the hotplug case we keep the task structs around and reuse
26 * them.
27 */
28static DEFINE_PER_CPU(struct task_struct *, idle_threads);
29
30struct task_struct *idle_thread_get(unsigned int cpu)
31{
32	struct task_struct *tsk = per_cpu(idle_threads, cpu);
33
34	if (!tsk)
35		return ERR_PTR(-ENOMEM);
36	return tsk;
37}
38
39void __init idle_thread_set_boot_cpu(void)
40{
41	per_cpu(idle_threads, smp_processor_id()) = current;
42}
43
44/**
45 * idle_init - Initialize the idle thread for a cpu
46 * @cpu:	The cpu for which the idle thread should be initialized
47 *
48 * Creates the thread if it does not exist.
49 */
50static __always_inline void idle_init(unsigned int cpu)
51{
52	struct task_struct *tsk = per_cpu(idle_threads, cpu);
53
54	if (!tsk) {
55		tsk = fork_idle(cpu);
56		if (IS_ERR(tsk))
57			pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
58		else
59			per_cpu(idle_threads, cpu) = tsk;
60	}
61}
62
63/**
64 * idle_threads_init - Initialize idle threads for all cpus
65 */
66void __init idle_threads_init(void)
67{
68	unsigned int cpu, boot_cpu;
69
70	boot_cpu = smp_processor_id();
71
72	for_each_possible_cpu(cpu) {
73		if (cpu != boot_cpu)
74			idle_init(cpu);
75	}
76}
77#endif
78
79#endif /* #ifdef CONFIG_SMP */
80
81static LIST_HEAD(hotplug_threads);
82static DEFINE_MUTEX(smpboot_threads_lock);
83
84struct smpboot_thread_data {
85	unsigned int			cpu;
86	unsigned int			status;
87	struct smp_hotplug_thread	*ht;
88};
89
90enum {
91	HP_THREAD_NONE = 0,
92	HP_THREAD_ACTIVE,
93	HP_THREAD_PARKED,
94};
95
96/**
97 * smpboot_thread_fn - percpu hotplug thread loop function
98 * @data:	thread data pointer
99 *
100 * Checks for thread stop and park conditions. Calls the necessary
101 * setup, cleanup, park and unpark functions for the registered
102 * thread.
103 *
104 * Returns 1 when the thread should exit, 0 otherwise.
105 */
106static int smpboot_thread_fn(void *data)
107{
108	struct smpboot_thread_data *td = data;
109	struct smp_hotplug_thread *ht = td->ht;
110
111	while (1) {
112		set_current_state(TASK_INTERRUPTIBLE);
113		preempt_disable();
114		if (kthread_should_stop()) {
115			__set_current_state(TASK_RUNNING);
116			preempt_enable();
117			/* cleanup must mirror setup */
118			if (ht->cleanup && td->status != HP_THREAD_NONE)
119				ht->cleanup(td->cpu, cpu_online(td->cpu));
120			kfree(td);
121			return 0;
122		}
123
124		if (kthread_should_park()) {
125			__set_current_state(TASK_RUNNING);
126			preempt_enable();
127			if (ht->park && td->status == HP_THREAD_ACTIVE) {
128				BUG_ON(td->cpu != smp_processor_id());
129				ht->park(td->cpu);
130				td->status = HP_THREAD_PARKED;
131			}
132			kthread_parkme();
133			/* We might have been woken for stop */
134			continue;
135		}
136
137		BUG_ON(td->cpu != smp_processor_id());
138
139		/* Check for state change setup */
140		switch (td->status) {
141		case HP_THREAD_NONE:
142			__set_current_state(TASK_RUNNING);
143			preempt_enable();
144			if (ht->setup)
145				ht->setup(td->cpu);
146			td->status = HP_THREAD_ACTIVE;
147			continue;
148
149		case HP_THREAD_PARKED:
150			__set_current_state(TASK_RUNNING);
151			preempt_enable();
152			if (ht->unpark)
153				ht->unpark(td->cpu);
154			td->status = HP_THREAD_ACTIVE;
155			continue;
156		}
157
158		if (!ht->thread_should_run(td->cpu)) {
159			preempt_enable_no_resched();
160			schedule();
161		} else {
162			__set_current_state(TASK_RUNNING);
163			preempt_enable();
164			ht->thread_fn(td->cpu);
165		}
166	}
167}
168
169static int
170__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
171{
172	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
173	struct smpboot_thread_data *td;
174
175	if (tsk)
176		return 0;
177
178	td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
179	if (!td)
180		return -ENOMEM;
181	td->cpu = cpu;
182	td->ht = ht;
183
184	tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
185				    ht->thread_comm);
186	if (IS_ERR(tsk)) {
187		kfree(td);
188		return PTR_ERR(tsk);
189	}
190	kthread_set_per_cpu(tsk, cpu);
191	/*
192	 * Park the thread so that it could start right on the CPU
193	 * when it is available.
194	 */
195	kthread_park(tsk);
196	get_task_struct(tsk);
197	*per_cpu_ptr(ht->store, cpu) = tsk;
198	if (ht->create) {
199		/*
200		 * Make sure that the task has actually scheduled out
201		 * into park position, before calling the create
202		 * callback. At least the migration thread callback
203		 * requires that the task is off the runqueue.
204		 */
205		if (!wait_task_inactive(tsk, TASK_PARKED))
206			WARN_ON(1);
207		else
208			ht->create(cpu);
209	}
210	return 0;
211}
212
213int smpboot_create_threads(unsigned int cpu)
214{
215	struct smp_hotplug_thread *cur;
216	int ret = 0;
217
218	mutex_lock(&smpboot_threads_lock);
219	list_for_each_entry(cur, &hotplug_threads, list) {
220		ret = __smpboot_create_thread(cur, cpu);
221		if (ret)
222			break;
223	}
224	mutex_unlock(&smpboot_threads_lock);
225	return ret;
226}
227
228static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
229{
230	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
231
232	if (!ht->selfparking)
233		kthread_unpark(tsk);
234}
235
236int smpboot_unpark_threads(unsigned int cpu)
237{
238	struct smp_hotplug_thread *cur;
239
240	mutex_lock(&smpboot_threads_lock);
241	list_for_each_entry(cur, &hotplug_threads, list)
242		smpboot_unpark_thread(cur, cpu);
243	mutex_unlock(&smpboot_threads_lock);
244	return 0;
245}
246
247static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
248{
249	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
250
251	if (tsk && !ht->selfparking)
252		kthread_park(tsk);
253}
254
255int smpboot_park_threads(unsigned int cpu)
256{
257	struct smp_hotplug_thread *cur;
258
259	mutex_lock(&smpboot_threads_lock);
260	list_for_each_entry_reverse(cur, &hotplug_threads, list)
261		smpboot_park_thread(cur, cpu);
262	mutex_unlock(&smpboot_threads_lock);
263	return 0;
264}
265
266static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
267{
268	unsigned int cpu;
269
270	/* We need to destroy also the parked threads of offline cpus */
271	for_each_possible_cpu(cpu) {
272		struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
273
274		if (tsk) {
275			kthread_stop_put(tsk);
276			*per_cpu_ptr(ht->store, cpu) = NULL;
277		}
278	}
279}
280
281/**
282 * smpboot_register_percpu_thread - Register a per_cpu thread related
283 * 					    to hotplug
284 * @plug_thread:	Hotplug thread descriptor
285 *
286 * Creates and starts the threads on all online cpus.
287 */
288int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
289{
290	unsigned int cpu;
291	int ret = 0;
292
293	cpus_read_lock();
294	mutex_lock(&smpboot_threads_lock);
295	for_each_online_cpu(cpu) {
296		ret = __smpboot_create_thread(plug_thread, cpu);
297		if (ret) {
298			smpboot_destroy_threads(plug_thread);
299			goto out;
300		}
301		smpboot_unpark_thread(plug_thread, cpu);
302	}
303	list_add(&plug_thread->list, &hotplug_threads);
304out:
305	mutex_unlock(&smpboot_threads_lock);
306	cpus_read_unlock();
307	return ret;
308}
309EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
310
311/**
312 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
313 * @plug_thread:	Hotplug thread descriptor
314 *
315 * Stops all threads on all possible cpus.
316 */
317void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
318{
319	cpus_read_lock();
320	mutex_lock(&smpboot_threads_lock);
321	list_del(&plug_thread->list);
322	smpboot_destroy_threads(plug_thread);
323	mutex_unlock(&smpboot_threads_lock);
324	cpus_read_unlock();
325}
326EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
327