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_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 */
smpboot_register_percpu_thread(struct smp_hotplug_thread * plug_thread)288 int 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);
304 out:
305 mutex_unlock(&smpboot_threads_lock);
306 cpus_read_unlock();
307 return ret;
308 }
309 EXPORT_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 */
smpboot_unregister_percpu_thread(struct smp_hotplug_thread * plug_thread)317 void 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 }
326 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
327