Line data Source code
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 6 : struct task_struct *idle_thread_get(unsigned int cpu)
31 : {
32 6 : struct task_struct *tsk = per_cpu(idle_threads, cpu);
33 :
34 6 : if (!tsk)
35 6 : return ERR_PTR(-ENOMEM);
36 6 : init_idle(tsk, cpu);
37 6 : return tsk;
38 : }
39 :
40 1 : void __init idle_thread_set_boot_cpu(void)
41 : {
42 1 : per_cpu(idle_threads, smp_processor_id()) = current;
43 1 : }
44 :
45 : /**
46 : * idle_init - Initialize the idle thread for a cpu
47 : * @cpu: The cpu for which the idle thread should be initialized
48 : *
49 : * Creates the thread if it does not exist.
50 : */
51 3 : static inline void idle_init(unsigned int cpu)
52 : {
53 3 : struct task_struct *tsk = per_cpu(idle_threads, cpu);
54 :
55 3 : if (!tsk) {
56 3 : tsk = fork_idle(cpu);
57 3 : if (IS_ERR(tsk))
58 0 : pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
59 : else
60 3 : per_cpu(idle_threads, cpu) = tsk;
61 : }
62 3 : }
63 :
64 : /**
65 : * idle_threads_init - Initialize idle threads for all cpus
66 : */
67 1 : void __init idle_threads_init(void)
68 : {
69 1 : unsigned int cpu, boot_cpu;
70 :
71 1 : boot_cpu = smp_processor_id();
72 :
73 5 : for_each_possible_cpu(cpu) {
74 4 : if (cpu != boot_cpu)
75 3 : idle_init(cpu);
76 : }
77 1 : }
78 : #endif
79 :
80 : #endif /* #ifdef CONFIG_SMP */
81 :
82 : static LIST_HEAD(hotplug_threads);
83 : static DEFINE_MUTEX(smpboot_threads_lock);
84 :
85 : struct smpboot_thread_data {
86 : unsigned int cpu;
87 : unsigned int status;
88 : struct smp_hotplug_thread *ht;
89 : };
90 :
91 : enum {
92 : HP_THREAD_NONE = 0,
93 : HP_THREAD_ACTIVE,
94 : HP_THREAD_PARKED,
95 : };
96 :
97 : /**
98 : * smpboot_thread_fn - percpu hotplug thread loop function
99 : * @data: thread data pointer
100 : *
101 : * Checks for thread stop and park conditions. Calls the necessary
102 : * setup, cleanup, park and unpark functions for the registered
103 : * thread.
104 : *
105 : * Returns 1 when the thread should exit, 0 otherwise.
106 : */
107 12 : static int smpboot_thread_fn(void *data)
108 : {
109 12 : struct smpboot_thread_data *td = data;
110 12 : struct smp_hotplug_thread *ht = td->ht;
111 :
112 7834 : while (1) {
113 7834 : set_current_state(TASK_INTERRUPTIBLE);
114 7836 : preempt_disable();
115 7836 : if (kthread_should_stop()) {
116 0 : __set_current_state(TASK_RUNNING);
117 0 : preempt_enable();
118 : /* cleanup must mirror setup */
119 0 : if (ht->cleanup && td->status != HP_THREAD_NONE)
120 0 : ht->cleanup(td->cpu, cpu_online(td->cpu));
121 0 : kfree(td);
122 0 : return 0;
123 : }
124 :
125 7835 : if (kthread_should_park()) {
126 0 : __set_current_state(TASK_RUNNING);
127 0 : preempt_enable();
128 0 : if (ht->park && td->status == HP_THREAD_ACTIVE) {
129 0 : BUG_ON(td->cpu != smp_processor_id());
130 0 : ht->park(td->cpu);
131 0 : td->status = HP_THREAD_PARKED;
132 : }
133 0 : kthread_parkme();
134 : /* We might have been woken for stop */
135 0 : continue;
136 : }
137 :
138 7836 : BUG_ON(td->cpu != smp_processor_id());
139 :
140 : /* Check for state change setup */
141 7836 : switch (td->status) {
142 : case HP_THREAD_NONE:
143 12 : __set_current_state(TASK_RUNNING);
144 12 : preempt_enable();
145 12 : if (ht->setup)
146 0 : ht->setup(td->cpu);
147 12 : td->status = HP_THREAD_ACTIVE;
148 12 : continue;
149 :
150 : case HP_THREAD_PARKED:
151 0 : __set_current_state(TASK_RUNNING);
152 0 : preempt_enable();
153 0 : if (ht->unpark)
154 0 : ht->unpark(td->cpu);
155 0 : td->status = HP_THREAD_ACTIVE;
156 0 : continue;
157 : }
158 :
159 7824 : if (!ht->thread_should_run(td->cpu)) {
160 1987 : preempt_enable_no_resched();
161 1987 : schedule();
162 : } else {
163 5836 : __set_current_state(TASK_RUNNING);
164 5836 : preempt_enable();
165 5836 : ht->thread_fn(td->cpu);
166 : }
167 : }
168 : }
169 :
170 : static int
171 12 : __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
172 : {
173 12 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
174 12 : struct smpboot_thread_data *td;
175 :
176 12 : if (tsk)
177 : return 0;
178 :
179 12 : td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
180 12 : if (!td)
181 : return -ENOMEM;
182 12 : td->cpu = cpu;
183 12 : td->ht = ht;
184 :
185 12 : tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
186 : ht->thread_comm);
187 12 : if (IS_ERR(tsk)) {
188 0 : kfree(td);
189 0 : return PTR_ERR(tsk);
190 : }
191 12 : kthread_set_per_cpu(tsk, cpu);
192 : /*
193 : * Park the thread so that it could start right on the CPU
194 : * when it is available.
195 : */
196 12 : kthread_park(tsk);
197 12 : get_task_struct(tsk);
198 12 : *per_cpu_ptr(ht->store, cpu) = tsk;
199 12 : if (ht->create) {
200 : /*
201 : * Make sure that the task has actually scheduled out
202 : * into park position, before calling the create
203 : * callback. At least the migration thread callback
204 : * requires that the task is off the runqueue.
205 : */
206 8 : if (!wait_task_inactive(tsk, TASK_PARKED))
207 0 : WARN_ON(1);
208 : else
209 8 : ht->create(cpu);
210 : }
211 : return 0;
212 : }
213 :
214 3 : int smpboot_create_threads(unsigned int cpu)
215 : {
216 3 : struct smp_hotplug_thread *cur;
217 3 : int ret = 0;
218 :
219 3 : mutex_lock(&smpboot_threads_lock);
220 12 : list_for_each_entry(cur, &hotplug_threads, list) {
221 9 : ret = __smpboot_create_thread(cur, cpu);
222 9 : if (ret)
223 : break;
224 : }
225 3 : mutex_unlock(&smpboot_threads_lock);
226 3 : return ret;
227 : }
228 :
229 12 : static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
230 : {
231 12 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
232 :
233 12 : if (!ht->selfparking)
234 4 : kthread_unpark(tsk);
235 12 : }
236 :
237 3 : int smpboot_unpark_threads(unsigned int cpu)
238 : {
239 3 : struct smp_hotplug_thread *cur;
240 :
241 3 : mutex_lock(&smpboot_threads_lock);
242 12 : list_for_each_entry(cur, &hotplug_threads, list)
243 9 : smpboot_unpark_thread(cur, cpu);
244 3 : mutex_unlock(&smpboot_threads_lock);
245 3 : return 0;
246 : }
247 :
248 0 : static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
249 : {
250 0 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
251 :
252 0 : if (tsk && !ht->selfparking)
253 0 : kthread_park(tsk);
254 0 : }
255 :
256 0 : int smpboot_park_threads(unsigned int cpu)
257 : {
258 0 : struct smp_hotplug_thread *cur;
259 :
260 0 : mutex_lock(&smpboot_threads_lock);
261 0 : list_for_each_entry_reverse(cur, &hotplug_threads, list)
262 0 : smpboot_park_thread(cur, cpu);
263 0 : mutex_unlock(&smpboot_threads_lock);
264 0 : return 0;
265 : }
266 :
267 0 : static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
268 : {
269 0 : unsigned int cpu;
270 :
271 : /* We need to destroy also the parked threads of offline cpus */
272 0 : for_each_possible_cpu(cpu) {
273 0 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
274 :
275 0 : if (tsk) {
276 0 : kthread_stop(tsk);
277 0 : put_task_struct(tsk);
278 0 : *per_cpu_ptr(ht->store, cpu) = NULL;
279 : }
280 : }
281 0 : }
282 :
283 : /**
284 : * smpboot_register_percpu_thread - Register a per_cpu thread related
285 : * to hotplug
286 : * @plug_thread: Hotplug thread descriptor
287 : *
288 : * Creates and starts the threads on all online cpus.
289 : */
290 3 : int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
291 : {
292 3 : unsigned int cpu;
293 3 : int ret = 0;
294 :
295 3 : get_online_cpus();
296 3 : mutex_lock(&smpboot_threads_lock);
297 9 : for_each_online_cpu(cpu) {
298 3 : ret = __smpboot_create_thread(plug_thread, cpu);
299 3 : if (ret) {
300 0 : smpboot_destroy_threads(plug_thread);
301 0 : goto out;
302 : }
303 3 : smpboot_unpark_thread(plug_thread, cpu);
304 : }
305 3 : list_add(&plug_thread->list, &hotplug_threads);
306 3 : out:
307 3 : mutex_unlock(&smpboot_threads_lock);
308 3 : put_online_cpus();
309 3 : return ret;
310 : }
311 : EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
312 :
313 : /**
314 : * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
315 : * @plug_thread: Hotplug thread descriptor
316 : *
317 : * Stops all threads on all possible cpus.
318 : */
319 0 : void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
320 : {
321 0 : get_online_cpus();
322 0 : mutex_lock(&smpboot_threads_lock);
323 0 : list_del(&plug_thread->list);
324 0 : smpboot_destroy_threads(plug_thread);
325 0 : mutex_unlock(&smpboot_threads_lock);
326 0 : put_online_cpus();
327 0 : }
328 : EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
329 :
330 : static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
331 :
332 : /*
333 : * Called to poll specified CPU's state, for example, when waiting for
334 : * a CPU to come online.
335 : */
336 0 : int cpu_report_state(int cpu)
337 : {
338 0 : return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
339 : }
340 :
341 : /*
342 : * If CPU has died properly, set its state to CPU_UP_PREPARE and
343 : * return success. Otherwise, return -EBUSY if the CPU died after
344 : * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
345 : * if cpu_wait_death() timed out and the CPU still hasn't gotten around
346 : * to dying. In the latter two cases, the CPU might not be set up
347 : * properly, but it is up to the arch-specific code to decide.
348 : * Finally, -EIO indicates an unanticipated problem.
349 : *
350 : * Note that it is permissible to omit this call entirely, as is
351 : * done in architectures that do no CPU-hotplug error checking.
352 : */
353 3 : int cpu_check_up_prepare(int cpu)
354 : {
355 3 : if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
356 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
357 : return 0;
358 : }
359 :
360 3 : switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
361 :
362 3 : case CPU_POST_DEAD:
363 :
364 : /* The CPU died properly, so just start it up again. */
365 3 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
366 3 : return 0;
367 :
368 : case CPU_DEAD_FROZEN:
369 :
370 : /*
371 : * Timeout during CPU death, so let caller know.
372 : * The outgoing CPU completed its processing, but after
373 : * cpu_wait_death() timed out and reported the error. The
374 : * caller is free to proceed, in which case the state
375 : * will be reset properly by cpu_set_state_online().
376 : * Proceeding despite this -EBUSY return makes sense
377 : * for systems where the outgoing CPUs take themselves
378 : * offline, with no post-death manipulation required from
379 : * a surviving CPU.
380 : */
381 : return -EBUSY;
382 :
383 0 : case CPU_BROKEN:
384 :
385 : /*
386 : * The most likely reason we got here is that there was
387 : * a timeout during CPU death, and the outgoing CPU never
388 : * did complete its processing. This could happen on
389 : * a virtualized system if the outgoing VCPU gets preempted
390 : * for more than five seconds, and the user attempts to
391 : * immediately online that same CPU. Trying again later
392 : * might return -EBUSY above, hence -EAGAIN.
393 : */
394 0 : return -EAGAIN;
395 :
396 0 : default:
397 :
398 : /* Should not happen. Famous last words. */
399 0 : return -EIO;
400 : }
401 : }
402 :
403 : /*
404 : * Mark the specified CPU online.
405 : *
406 : * Note that it is permissible to omit this call entirely, as is
407 : * done in architectures that do no CPU-hotplug error checking.
408 : */
409 4 : void cpu_set_state_online(int cpu)
410 : {
411 4 : (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
412 4 : }
413 :
414 : #ifdef CONFIG_HOTPLUG_CPU
415 :
416 : /*
417 : * Wait for the specified CPU to exit the idle loop and die.
418 : */
419 0 : bool cpu_wait_death(unsigned int cpu, int seconds)
420 : {
421 0 : int jf_left = seconds * HZ;
422 0 : int oldstate;
423 0 : bool ret = true;
424 0 : int sleep_jf = 1;
425 :
426 0 : might_sleep();
427 :
428 : /* The outgoing CPU will normally get done quite quickly. */
429 0 : if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
430 0 : goto update_state;
431 0 : udelay(5);
432 :
433 : /* But if the outgoing CPU dawdles, wait increasingly long times. */
434 0 : while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
435 0 : schedule_timeout_uninterruptible(sleep_jf);
436 0 : jf_left -= sleep_jf;
437 0 : if (jf_left <= 0)
438 : break;
439 0 : sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
440 : }
441 0 : update_state:
442 0 : oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
443 0 : if (oldstate == CPU_DEAD) {
444 : /* Outgoing CPU died normally, update state. */
445 0 : smp_mb(); /* atomic_read() before update. */
446 0 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
447 : } else {
448 : /* Outgoing CPU still hasn't died, set state accordingly. */
449 0 : if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
450 : oldstate, CPU_BROKEN) != oldstate)
451 0 : goto update_state;
452 : ret = false;
453 : }
454 0 : return ret;
455 : }
456 :
457 : /*
458 : * Called by the outgoing CPU to report its successful death. Return
459 : * false if this report follows the surviving CPU's timing out.
460 : *
461 : * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
462 : * timed out. This approach allows architectures to omit calls to
463 : * cpu_check_up_prepare() and cpu_set_state_online() without defeating
464 : * the next cpu_wait_death()'s polling loop.
465 : */
466 0 : bool cpu_report_death(void)
467 : {
468 0 : int oldstate;
469 0 : int newstate;
470 0 : int cpu = smp_processor_id();
471 :
472 0 : do {
473 0 : oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
474 0 : if (oldstate != CPU_BROKEN)
475 : newstate = CPU_DEAD;
476 : else
477 0 : newstate = CPU_DEAD_FROZEN;
478 0 : } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
479 0 : oldstate, newstate) != oldstate);
480 0 : return newstate == CPU_DEAD;
481 : }
482 :
483 : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
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