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 | |
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(error: -ENOMEM); |
36 | return tsk; |
37 | } |
38 | |
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 | */ |
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(ptr: 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 | */ |
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 | */ |
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(cpu: td->cpu)); |
120 | kfree(objp: 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 |
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(size: 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(threadfn: smpboot_thread_fn, data: td, cpu, |
185 | namefmt: ht->thread_comm); |
186 | if (IS_ERR(ptr: tsk)) { |
187 | kfree(objp: td); |
188 | return PTR_ERR(ptr: tsk); |
189 | } |
190 | kthread_set_per_cpu(k: 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(k: tsk); |
196 | get_task_struct(t: 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 | |
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(ht: cur, cpu); |
221 | if (ret) |
222 | break; |
223 | } |
224 | mutex_unlock(lock: &smpboot_threads_lock); |
225 | return ret; |
226 | } |
227 | |
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(k: tsk); |
234 | } |
235 | |
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(ht: cur, cpu); |
243 | mutex_unlock(lock: &smpboot_threads_lock); |
244 | return 0; |
245 | } |
246 | |
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(k: tsk); |
253 | } |
254 | |
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(ht: cur, cpu); |
262 | mutex_unlock(lock: &smpboot_threads_lock); |
263 | return 0; |
264 | } |
265 | |
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(k: 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 | */ |
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(ht: plug_thread, cpu); |
297 | if (ret) { |
298 | smpboot_destroy_threads(ht: plug_thread); |
299 | goto out; |
300 | } |
301 | smpboot_unpark_thread(ht: plug_thread, cpu); |
302 | } |
303 | list_add(new: &plug_thread->list, head: &hotplug_threads); |
304 | out: |
305 | mutex_unlock(lock: &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 | */ |
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(entry: &plug_thread->list); |
322 | smpboot_destroy_threads(ht: plug_thread); |
323 | mutex_unlock(lock: &smpboot_threads_lock); |
324 | cpus_read_unlock(); |
325 | } |
326 | EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); |
327 | |