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 : 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 :
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(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 1 : static int smpboot_thread_fn(void *data)
107 : {
108 1 : struct smpboot_thread_data *td = data;
109 1 : struct smp_hotplug_thread *ht = td->ht;
110 :
111 : while (1) {
112 780 : set_current_state(TASK_INTERRUPTIBLE);
113 780 : preempt_disable();
114 780 : if (kthread_should_stop()) {
115 0 : __set_current_state(TASK_RUNNING);
116 0 : preempt_enable();
117 : /* cleanup must mirror setup */
118 0 : if (ht->cleanup && td->status != HP_THREAD_NONE)
119 0 : ht->cleanup(td->cpu, cpu_online(td->cpu));
120 0 : kfree(td);
121 0 : return 0;
122 : }
123 :
124 780 : if (kthread_should_park()) {
125 0 : __set_current_state(TASK_RUNNING);
126 0 : preempt_enable();
127 0 : if (ht->park && td->status == HP_THREAD_ACTIVE) {
128 0 : BUG_ON(td->cpu != smp_processor_id());
129 0 : ht->park(td->cpu);
130 0 : td->status = HP_THREAD_PARKED;
131 : }
132 0 : kthread_parkme();
133 : /* We might have been woken for stop */
134 0 : continue;
135 : }
136 :
137 780 : BUG_ON(td->cpu != smp_processor_id());
138 :
139 : /* Check for state change setup */
140 780 : switch (td->status) {
141 : case HP_THREAD_NONE:
142 1 : __set_current_state(TASK_RUNNING);
143 1 : preempt_enable();
144 1 : if (ht->setup)
145 0 : ht->setup(td->cpu);
146 1 : td->status = HP_THREAD_ACTIVE;
147 1 : continue;
148 :
149 : case HP_THREAD_PARKED:
150 0 : __set_current_state(TASK_RUNNING);
151 0 : preempt_enable();
152 0 : if (ht->unpark)
153 0 : ht->unpark(td->cpu);
154 0 : td->status = HP_THREAD_ACTIVE;
155 0 : continue;
156 : }
157 :
158 779 : if (!ht->thread_should_run(td->cpu)) {
159 390 : preempt_enable_no_resched();
160 390 : schedule();
161 : } else {
162 389 : __set_current_state(TASK_RUNNING);
163 389 : preempt_enable();
164 389 : ht->thread_fn(td->cpu);
165 : }
166 : }
167 : }
168 :
169 : static int
170 1 : __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
171 : {
172 1 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
173 : struct smpboot_thread_data *td;
174 :
175 1 : if (tsk)
176 : return 0;
177 :
178 1 : td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
179 1 : if (!td)
180 : return -ENOMEM;
181 1 : td->cpu = cpu;
182 1 : td->ht = ht;
183 :
184 1 : tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
185 : ht->thread_comm);
186 1 : if (IS_ERR(tsk)) {
187 0 : kfree(td);
188 0 : return PTR_ERR(tsk);
189 : }
190 1 : 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 1 : kthread_park(tsk);
196 1 : get_task_struct(tsk);
197 1 : *per_cpu_ptr(ht->store, cpu) = tsk;
198 1 : 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 0 : if (!wait_task_inactive(tsk, TASK_PARKED))
206 : WARN_ON(1);
207 : else
208 0 : ht->create(cpu);
209 : }
210 : return 0;
211 : }
212 :
213 0 : int smpboot_create_threads(unsigned int cpu)
214 : {
215 : struct smp_hotplug_thread *cur;
216 0 : int ret = 0;
217 :
218 0 : mutex_lock(&smpboot_threads_lock);
219 0 : list_for_each_entry(cur, &hotplug_threads, list) {
220 0 : ret = __smpboot_create_thread(cur, cpu);
221 0 : if (ret)
222 : break;
223 : }
224 0 : mutex_unlock(&smpboot_threads_lock);
225 0 : return ret;
226 : }
227 :
228 : static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
229 : {
230 1 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
231 :
232 1 : if (!ht->selfparking)
233 1 : kthread_unpark(tsk);
234 : }
235 :
236 0 : int smpboot_unpark_threads(unsigned int cpu)
237 : {
238 : struct smp_hotplug_thread *cur;
239 :
240 0 : mutex_lock(&smpboot_threads_lock);
241 0 : list_for_each_entry(cur, &hotplug_threads, list)
242 0 : smpboot_unpark_thread(cur, cpu);
243 0 : mutex_unlock(&smpboot_threads_lock);
244 0 : return 0;
245 : }
246 :
247 : static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
248 : {
249 0 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
250 :
251 0 : if (tsk && !ht->selfparking)
252 0 : kthread_park(tsk);
253 : }
254 :
255 0 : int smpboot_park_threads(unsigned int cpu)
256 : {
257 : struct smp_hotplug_thread *cur;
258 :
259 0 : mutex_lock(&smpboot_threads_lock);
260 0 : list_for_each_entry_reverse(cur, &hotplug_threads, list)
261 0 : smpboot_park_thread(cur, cpu);
262 0 : mutex_unlock(&smpboot_threads_lock);
263 0 : return 0;
264 : }
265 :
266 0 : 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 0 : for_each_possible_cpu(cpu) {
272 0 : struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
273 :
274 0 : if (tsk) {
275 0 : kthread_stop(tsk);
276 0 : put_task_struct(tsk);
277 0 : *per_cpu_ptr(ht->store, cpu) = NULL;
278 : }
279 : }
280 0 : }
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 : */
289 1 : int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
290 : {
291 : unsigned int cpu;
292 1 : int ret = 0;
293 :
294 : cpus_read_lock();
295 1 : mutex_lock(&smpboot_threads_lock);
296 2 : for_each_online_cpu(cpu) {
297 1 : ret = __smpboot_create_thread(plug_thread, cpu);
298 1 : if (ret) {
299 0 : smpboot_destroy_threads(plug_thread);
300 0 : goto out;
301 : }
302 2 : smpboot_unpark_thread(plug_thread, cpu);
303 : }
304 1 : list_add(&plug_thread->list, &hotplug_threads);
305 : out:
306 1 : mutex_unlock(&smpboot_threads_lock);
307 : cpus_read_unlock();
308 1 : 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 : */
318 0 : void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
319 : {
320 : cpus_read_lock();
321 0 : mutex_lock(&smpboot_threads_lock);
322 0 : list_del(&plug_thread->list);
323 0 : smpboot_destroy_threads(plug_thread);
324 0 : mutex_unlock(&smpboot_threads_lock);
325 : cpus_read_unlock();
326 0 : }
327 : EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
328 :
329 : static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
330 :
331 : /*
332 : * Called to poll specified CPU's state, for example, when waiting for
333 : * a CPU to come online.
334 : */
335 0 : int cpu_report_state(int cpu)
336 : {
337 0 : return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
338 : }
339 :
340 : /*
341 : * If CPU has died properly, set its state to CPU_UP_PREPARE and
342 : * return success. Otherwise, return -EBUSY if the CPU died after
343 : * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
344 : * if cpu_wait_death() timed out and the CPU still hasn't gotten around
345 : * to dying. In the latter two cases, the CPU might not be set up
346 : * properly, but it is up to the arch-specific code to decide.
347 : * Finally, -EIO indicates an unanticipated problem.
348 : *
349 : * Note that it is permissible to omit this call entirely, as is
350 : * done in architectures that do no CPU-hotplug error checking.
351 : */
352 0 : int cpu_check_up_prepare(int cpu)
353 : {
354 : if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
355 0 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
356 : return 0;
357 : }
358 :
359 : switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
360 :
361 : case CPU_POST_DEAD:
362 :
363 : /* The CPU died properly, so just start it up again. */
364 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
365 : return 0;
366 :
367 : case CPU_DEAD_FROZEN:
368 :
369 : /*
370 : * Timeout during CPU death, so let caller know.
371 : * The outgoing CPU completed its processing, but after
372 : * cpu_wait_death() timed out and reported the error. The
373 : * caller is free to proceed, in which case the state
374 : * will be reset properly by cpu_set_state_online().
375 : * Proceeding despite this -EBUSY return makes sense
376 : * for systems where the outgoing CPUs take themselves
377 : * offline, with no post-death manipulation required from
378 : * a surviving CPU.
379 : */
380 : return -EBUSY;
381 :
382 : case CPU_BROKEN:
383 :
384 : /*
385 : * The most likely reason we got here is that there was
386 : * a timeout during CPU death, and the outgoing CPU never
387 : * did complete its processing. This could happen on
388 : * a virtualized system if the outgoing VCPU gets preempted
389 : * for more than five seconds, and the user attempts to
390 : * immediately online that same CPU. Trying again later
391 : * might return -EBUSY above, hence -EAGAIN.
392 : */
393 : return -EAGAIN;
394 :
395 : case CPU_UP_PREPARE:
396 : /*
397 : * Timeout while waiting for the CPU to show up. Allow to try
398 : * again later.
399 : */
400 : return 0;
401 :
402 : default:
403 :
404 : /* Should not happen. Famous last words. */
405 : return -EIO;
406 : }
407 : }
408 :
409 : /*
410 : * Mark the specified CPU online.
411 : *
412 : * Note that it is permissible to omit this call entirely, as is
413 : * done in architectures that do no CPU-hotplug error checking.
414 : */
415 0 : void cpu_set_state_online(int cpu)
416 : {
417 0 : (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
418 0 : }
419 :
420 : #ifdef CONFIG_HOTPLUG_CPU
421 :
422 : /*
423 : * Wait for the specified CPU to exit the idle loop and die.
424 : */
425 : bool cpu_wait_death(unsigned int cpu, int seconds)
426 : {
427 : int jf_left = seconds * HZ;
428 : int oldstate;
429 : bool ret = true;
430 : int sleep_jf = 1;
431 :
432 : might_sleep();
433 :
434 : /* The outgoing CPU will normally get done quite quickly. */
435 : if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
436 : goto update_state_early;
437 : udelay(5);
438 :
439 : /* But if the outgoing CPU dawdles, wait increasingly long times. */
440 : while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
441 : schedule_timeout_uninterruptible(sleep_jf);
442 : jf_left -= sleep_jf;
443 : if (jf_left <= 0)
444 : break;
445 : sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
446 : }
447 : update_state_early:
448 : oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
449 : update_state:
450 : if (oldstate == CPU_DEAD) {
451 : /* Outgoing CPU died normally, update state. */
452 : smp_mb(); /* atomic_read() before update. */
453 : atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
454 : } else {
455 : /* Outgoing CPU still hasn't died, set state accordingly. */
456 : if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
457 : &oldstate, CPU_BROKEN))
458 : goto update_state;
459 : ret = false;
460 : }
461 : return ret;
462 : }
463 :
464 : /*
465 : * Called by the outgoing CPU to report its successful death. Return
466 : * false if this report follows the surviving CPU's timing out.
467 : *
468 : * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
469 : * timed out. This approach allows architectures to omit calls to
470 : * cpu_check_up_prepare() and cpu_set_state_online() without defeating
471 : * the next cpu_wait_death()'s polling loop.
472 : */
473 : bool cpu_report_death(void)
474 : {
475 : int oldstate;
476 : int newstate;
477 : int cpu = smp_processor_id();
478 :
479 : oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
480 : do {
481 : if (oldstate != CPU_BROKEN)
482 : newstate = CPU_DEAD;
483 : else
484 : newstate = CPU_DEAD_FROZEN;
485 : } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
486 : &oldstate, newstate));
487 : return newstate == CPU_DEAD;
488 : }
489 :
490 : #endif /* #ifdef CONFIG_HOTPLUG_CPU */
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