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  */
28 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
29 
idle_thread_get(unsigned int cpu)30 struct 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 
idle_thread_set_boot_cpu(void)39 void __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  */
idle_init(unsigned int cpu)50 static __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  */
idle_threads_init(void)66 void __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 
81 static LIST_HEAD(hotplug_threads);
82 static DEFINE_MUTEX(smpboot_threads_lock);
83 
84 struct smpboot_thread_data {
85 	unsigned int			cpu;
86 	unsigned int			status;
87 	struct smp_hotplug_thread	*ht;
88 };
89 
90 enum {
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  */
smpboot_thread_fn(void * data)106 static 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 
169 static int
__smpboot_create_thread(struct smp_hotplug_thread * ht,unsigned int cpu)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 
smpboot_create_threads(unsigned int cpu)213 int 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 
smpboot_unpark_thread(struct smp_hotplug_thread * ht,unsigned int cpu)228 static 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 
smpboot_unpark_threads(unsigned int cpu)236 int 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 
smpboot_park_thread(struct smp_hotplug_thread * ht,unsigned int cpu)247 static 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 
smpboot_park_threads(unsigned int cpu)255 int 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 
smpboot_destroy_threads(struct smp_hotplug_thread * ht)266 static 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(tsk);
276 			put_task_struct(tsk);
277 			*per_cpu_ptr(ht->store, cpu) = NULL;
278 		}
279 	}
280 }
281 
282 /**
283  * smpboot_register_percpu_thread - Register a per_cpu thread related
284  * 					    to hotplug
285  * @plug_thread:	Hotplug thread descriptor
286  *
287  * Creates and starts the threads on all online cpus.
288  */
smpboot_register_percpu_thread(struct smp_hotplug_thread * plug_thread)289 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
290 {
291 	unsigned int cpu;
292 	int ret = 0;
293 
294 	cpus_read_lock();
295 	mutex_lock(&smpboot_threads_lock);
296 	for_each_online_cpu(cpu) {
297 		ret = __smpboot_create_thread(plug_thread, cpu);
298 		if (ret) {
299 			smpboot_destroy_threads(plug_thread);
300 			goto out;
301 		}
302 		smpboot_unpark_thread(plug_thread, cpu);
303 	}
304 	list_add(&plug_thread->list, &hotplug_threads);
305 out:
306 	mutex_unlock(&smpboot_threads_lock);
307 	cpus_read_unlock();
308 	return ret;
309 }
310 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
311 
312 /**
313  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
314  * @plug_thread:	Hotplug thread descriptor
315  *
316  * Stops all threads on all possible cpus.
317  */
smpboot_unregister_percpu_thread(struct smp_hotplug_thread * plug_thread)318 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
319 {
320 	cpus_read_lock();
321 	mutex_lock(&smpboot_threads_lock);
322 	list_del(&plug_thread->list);
323 	smpboot_destroy_threads(plug_thread);
324 	mutex_unlock(&smpboot_threads_lock);
325 	cpus_read_unlock();
326 }
327 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
328