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 */
26 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
27
idle_thread_get(unsigned int cpu)28 struct 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
idle_thread_set_boot_cpu(void)37 void __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 */
idle_init(unsigned int cpu)48 static __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 */
idle_threads_init(void)64 void __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 static LIST_HEAD(hotplug_threads);
78 static DEFINE_MUTEX(smpboot_threads_lock);
79
80 struct smpboot_thread_data {
81 unsigned int cpu;
82 unsigned int status;
83 struct smp_hotplug_thread *ht;
84 };
85
86 enum {
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 */
smpboot_thread_fn(void * data)102 static int smpboot_thread_fn(void *data)
103 {
104 struct smpboot_thread_data *td = data;
105 struct smp_hotplug_thread *ht = td->ht;
106 bool should_run;
107
108 while (1) {
109 set_current_state(TASK_INTERRUPTIBLE);
110 preempt_disable();
111 if (kthread_should_stop()) {
112 __set_current_state(TASK_RUNNING);
113 preempt_enable();
114 /* cleanup must mirror setup */
115 if (ht->cleanup && td->status != HP_THREAD_NONE)
116 ht->cleanup(td->cpu, cpu_online(td->cpu));
117 kfree(td);
118 return 0;
119 }
120
121 should_run = td->status == HP_THREAD_ACTIVE && ht->thread_should_run(td->cpu);
122 if (kthread_should_park() && !should_run) {
123 __set_current_state(TASK_RUNNING);
124 preempt_enable();
125 if (ht->park && td->status == HP_THREAD_ACTIVE) {
126 BUG_ON(td->cpu != smp_processor_id());
127 ht->park(td->cpu);
128 td->status = HP_THREAD_PARKED;
129 }
130 kthread_parkme();
131 /* We might have been woken for stop */
132 continue;
133 }
134
135 BUG_ON(td->cpu != smp_processor_id());
136
137 /* Check for state change setup */
138 switch (td->status) {
139 case HP_THREAD_NONE:
140 __set_current_state(TASK_RUNNING);
141 preempt_enable();
142 if (ht->setup)
143 ht->setup(td->cpu);
144 td->status = HP_THREAD_ACTIVE;
145 continue;
146
147 case HP_THREAD_PARKED:
148 __set_current_state(TASK_RUNNING);
149 preempt_enable();
150 if (ht->unpark)
151 ht->unpark(td->cpu);
152 td->status = HP_THREAD_ACTIVE;
153 continue;
154 }
155
156 if (!should_run) {
157 preempt_enable_no_resched();
158 schedule();
159 } else {
160 __set_current_state(TASK_RUNNING);
161 preempt_enable();
162 ht->thread_fn(td->cpu);
163 }
164 }
165 }
166
167 static int
__smpboot_create_thread(struct smp_hotplug_thread * ht,unsigned int cpu)168 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
169 {
170 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
171 struct smpboot_thread_data *td;
172
173 if (tsk)
174 return 0;
175
176 td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
177 if (!td)
178 return -ENOMEM;
179 td->cpu = cpu;
180 td->ht = ht;
181
182 tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
183 ht->thread_comm);
184 if (IS_ERR(tsk)) {
185 kfree(td);
186 return PTR_ERR(tsk);
187 }
188 kthread_set_per_cpu(tsk, cpu);
189 /*
190 * Park the thread so that it could start right on the CPU
191 * when it is available.
192 */
193 kthread_park(tsk);
194 get_task_struct(tsk);
195 *per_cpu_ptr(ht->store, cpu) = tsk;
196 if (ht->create) {
197 /*
198 * Make sure that the task has actually scheduled out
199 * into park position, before calling the create
200 * callback. At least the migration thread callback
201 * requires that the task is off the runqueue.
202 */
203 if (!wait_task_inactive(tsk, TASK_PARKED))
204 WARN_ON(1);
205 else
206 ht->create(cpu);
207 }
208 return 0;
209 }
210
smpboot_create_threads(unsigned int cpu)211 int smpboot_create_threads(unsigned int cpu)
212 {
213 struct smp_hotplug_thread *cur;
214 int ret = 0;
215
216 mutex_lock(&smpboot_threads_lock);
217 list_for_each_entry(cur, &hotplug_threads, list) {
218 ret = __smpboot_create_thread(cur, cpu);
219 if (ret)
220 break;
221 }
222 mutex_unlock(&smpboot_threads_lock);
223 return ret;
224 }
225
smpboot_unpark_thread(struct smp_hotplug_thread * ht,unsigned int cpu)226 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
227 {
228 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
229
230 if (!ht->selfparking)
231 kthread_unpark(tsk);
232 }
233
smpboot_unpark_threads(unsigned int cpu)234 int smpboot_unpark_threads(unsigned int cpu)
235 {
236 struct smp_hotplug_thread *cur;
237
238 mutex_lock(&smpboot_threads_lock);
239 list_for_each_entry(cur, &hotplug_threads, list)
240 smpboot_unpark_thread(cur, cpu);
241 mutex_unlock(&smpboot_threads_lock);
242 return 0;
243 }
244
smpboot_park_thread(struct smp_hotplug_thread * ht,unsigned int cpu)245 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
246 {
247 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
248
249 if (tsk && !ht->selfparking)
250 kthread_park(tsk);
251 }
252
smpboot_park_threads(unsigned int cpu)253 int smpboot_park_threads(unsigned int cpu)
254 {
255 struct smp_hotplug_thread *cur;
256
257 mutex_lock(&smpboot_threads_lock);
258 list_for_each_entry_reverse(cur, &hotplug_threads, list)
259 smpboot_park_thread(cur, cpu);
260 mutex_unlock(&smpboot_threads_lock);
261 return 0;
262 }
263
smpboot_destroy_threads(struct smp_hotplug_thread * ht)264 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
265 {
266 unsigned int cpu;
267
268 /* We need to destroy also the parked threads of offline cpus */
269 for_each_possible_cpu(cpu) {
270 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
271
272 if (tsk) {
273 kthread_stop_put(tsk);
274 *per_cpu_ptr(ht->store, cpu) = NULL;
275 }
276 }
277 }
278
279 /**
280 * smpboot_register_percpu_thread - Register a per_cpu thread related
281 * to hotplug
282 * @plug_thread: Hotplug thread descriptor
283 *
284 * Creates and starts the threads on all online cpus.
285 */
smpboot_register_percpu_thread(struct smp_hotplug_thread * plug_thread)286 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
287 {
288 unsigned int cpu;
289 int ret = 0;
290
291 cpus_read_lock();
292 mutex_lock(&smpboot_threads_lock);
293 for_each_online_cpu(cpu) {
294 ret = __smpboot_create_thread(plug_thread, cpu);
295 if (ret) {
296 smpboot_destroy_threads(plug_thread);
297 goto out;
298 }
299 smpboot_unpark_thread(plug_thread, cpu);
300 }
301 list_add(&plug_thread->list, &hotplug_threads);
302 out:
303 mutex_unlock(&smpboot_threads_lock);
304 cpus_read_unlock();
305 return ret;
306 }
307 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
308
309 /**
310 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
311 * @plug_thread: Hotplug thread descriptor
312 *
313 * Stops all threads on all possible cpus.
314 */
smpboot_unregister_percpu_thread(struct smp_hotplug_thread * plug_thread)315 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
316 {
317 cpus_read_lock();
318 mutex_lock(&smpboot_threads_lock);
319 list_del(&plug_thread->list);
320 smpboot_destroy_threads(plug_thread);
321 mutex_unlock(&smpboot_threads_lock);
322 cpus_read_unlock();
323 }
324 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
325