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1/*
2 * Common SMP CPU bringup/teardown functions
3 */
4#include <linux/cpu.h>
5#include <linux/err.h>
6#include <linux/smp.h>
7#include <linux/delay.h>
8#include <linux/init.h>
9#include <linux/list.h>
10#include <linux/slab.h>
11#include <linux/sched.h>
12#include <linux/export.h>
13#include <linux/percpu.h>
14#include <linux/kthread.h>
15#include <linux/smpboot.h>
16
17#include "smpboot.h"
18
19#ifdef CONFIG_SMP
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 */
26static DEFINE_PER_CPU(struct task_struct *, idle_threads);
27
28struct 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 init_idle(tsk, cpu);
35 return tsk;
36}
37
38void __init idle_thread_set_boot_cpu(void)
39{
40 per_cpu(idle_threads, smp_processor_id()) = current;
41}
42
43/**
44 * idle_init - Initialize the idle thread for a cpu
45 * @cpu: The cpu for which the idle thread should be initialized
46 *
47 * Creates the thread if it does not exist.
48 */
49static inline void idle_init(unsigned int cpu)
50{
51 struct task_struct *tsk = per_cpu(idle_threads, cpu);
52
53 if (!tsk) {
54 tsk = fork_idle(cpu);
55 if (IS_ERR(tsk))
56 pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
57 else
58 per_cpu(idle_threads, cpu) = tsk;
59 }
60}
61
62/**
63 * idle_threads_init - Initialize idle threads for all cpus
64 */
65void __init idle_threads_init(void)
66{
67 unsigned int cpu, boot_cpu;
68
69 boot_cpu = smp_processor_id();
70
71 for_each_possible_cpu(cpu) {
72 if (cpu != boot_cpu)
73 idle_init(cpu);
74 }
75}
76#endif
77
78#endif /* #ifdef CONFIG_SMP */
79
80static LIST_HEAD(hotplug_threads);
81static DEFINE_MUTEX(smpboot_threads_lock);
82
83struct smpboot_thread_data {
84 unsigned int cpu;
85 unsigned int status;
86 struct smp_hotplug_thread *ht;
87};
88
89enum {
90 HP_THREAD_NONE = 0,
91 HP_THREAD_ACTIVE,
92 HP_THREAD_PARKED,
93};
94
95/**
96 * smpboot_thread_fn - percpu hotplug thread loop function
97 * @data: thread data pointer
98 *
99 * Checks for thread stop and park conditions. Calls the necessary
100 * setup, cleanup, park and unpark functions for the registered
101 * thread.
102 *
103 * Returns 1 when the thread should exit, 0 otherwise.
104 */
105static int smpboot_thread_fn(void *data)
106{
107 struct smpboot_thread_data *td = data;
108 struct smp_hotplug_thread *ht = td->ht;
109
110 while (1) {
111 set_current_state(TASK_INTERRUPTIBLE);
112 preempt_disable();
113 if (kthread_should_stop()) {
114 __set_current_state(TASK_RUNNING);
115 preempt_enable();
116 /* cleanup must mirror setup */
117 if (ht->cleanup && td->status != HP_THREAD_NONE)
118 ht->cleanup(td->cpu, cpu_online(td->cpu));
119 kfree(td);
120 return 0;
121 }
122
123 if (kthread_should_park()) {
124 __set_current_state(TASK_RUNNING);
125 preempt_enable();
126 if (ht->park && td->status == HP_THREAD_ACTIVE) {
127 BUG_ON(td->cpu != smp_processor_id());
128 ht->park(td->cpu);
129 td->status = HP_THREAD_PARKED;
130 }
131 kthread_parkme();
132 /* We might have been woken for stop */
133 continue;
134 }
135
136 BUG_ON(td->cpu != smp_processor_id());
137
138 /* Check for state change setup */
139 switch (td->status) {
140 case HP_THREAD_NONE:
141 __set_current_state(TASK_RUNNING);
142 preempt_enable();
143 if (ht->setup)
144 ht->setup(td->cpu);
145 td->status = HP_THREAD_ACTIVE;
146 continue;
147
148 case HP_THREAD_PARKED:
149 __set_current_state(TASK_RUNNING);
150 preempt_enable();
151 if (ht->unpark)
152 ht->unpark(td->cpu);
153 td->status = HP_THREAD_ACTIVE;
154 continue;
155 }
156
157 if (!ht->thread_should_run(td->cpu)) {
158 preempt_enable_no_resched();
159 schedule();
160 } else {
161 __set_current_state(TASK_RUNNING);
162 preempt_enable();
163 ht->thread_fn(td->cpu);
164 }
165 }
166}
167
168static int
169__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
170{
171 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
172 struct smpboot_thread_data *td;
173
174 if (tsk)
175 return 0;
176
177 td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
178 if (!td)
179 return -ENOMEM;
180 td->cpu = cpu;
181 td->ht = ht;
182
183 tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
184 ht->thread_comm);
185 if (IS_ERR(tsk)) {
186 kfree(td);
187 return PTR_ERR(tsk);
188 }
189 get_task_struct(tsk);
190 *per_cpu_ptr(ht->store, cpu) = tsk;
191 if (ht->create) {
192 /*
193 * Make sure that the task has actually scheduled out
194 * into park position, before calling the create
195 * callback. At least the migration thread callback
196 * requires that the task is off the runqueue.
197 */
198 if (!wait_task_inactive(tsk, TASK_PARKED))
199 WARN_ON(1);
200 else
201 ht->create(cpu);
202 }
203 return 0;
204}
205
206int smpboot_create_threads(unsigned int cpu)
207{
208 struct smp_hotplug_thread *cur;
209 int ret = 0;
210
211 mutex_lock(&smpboot_threads_lock);
212 list_for_each_entry(cur, &hotplug_threads, list) {
213 ret = __smpboot_create_thread(cur, cpu);
214 if (ret)
215 break;
216 }
217 mutex_unlock(&smpboot_threads_lock);
218 return ret;
219}
220
221static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
222{
223 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
224
225 if (!ht->selfparking)
226 kthread_unpark(tsk);
227}
228
229int smpboot_unpark_threads(unsigned int cpu)
230{
231 struct smp_hotplug_thread *cur;
232
233 mutex_lock(&smpboot_threads_lock);
234 list_for_each_entry(cur, &hotplug_threads, list)
235 if (cpumask_test_cpu(cpu, cur->cpumask))
236 smpboot_unpark_thread(cur, cpu);
237 mutex_unlock(&smpboot_threads_lock);
238 return 0;
239}
240
241static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
242{
243 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
244
245 if (tsk && !ht->selfparking)
246 kthread_park(tsk);
247}
248
249int smpboot_park_threads(unsigned int cpu)
250{
251 struct smp_hotplug_thread *cur;
252
253 mutex_lock(&smpboot_threads_lock);
254 list_for_each_entry_reverse(cur, &hotplug_threads, list)
255 smpboot_park_thread(cur, cpu);
256 mutex_unlock(&smpboot_threads_lock);
257 return 0;
258}
259
260static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
261{
262 unsigned int cpu;
263
264 /* We need to destroy also the parked threads of offline cpus */
265 for_each_possible_cpu(cpu) {
266 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
267
268 if (tsk) {
269 kthread_stop(tsk);
270 put_task_struct(tsk);
271 *per_cpu_ptr(ht->store, cpu) = NULL;
272 }
273 }
274}
275
276/**
277 * smpboot_register_percpu_thread_cpumask - Register a per_cpu thread related
278 * to hotplug
279 * @plug_thread: Hotplug thread descriptor
280 * @cpumask: The cpumask where threads run
281 *
282 * Creates and starts the threads on all online cpus.
283 */
284int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread,
285 const struct cpumask *cpumask)
286{
287 unsigned int cpu;
288 int ret = 0;
289
290 if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
291 return -ENOMEM;
292 cpumask_copy(plug_thread->cpumask, cpumask);
293
294 get_online_cpus();
295 mutex_lock(&smpboot_threads_lock);
296 for_each_online_cpu(cpu) {
297 ret = __smpboot_create_thread(plug_thread, cpu);
298 if (ret) {
299 smpboot_destroy_threads(plug_thread);
300 free_cpumask_var(plug_thread->cpumask);
301 goto out;
302 }
303 if (cpumask_test_cpu(cpu, cpumask))
304 smpboot_unpark_thread(plug_thread, cpu);
305 }
306 list_add(&plug_thread->list, &hotplug_threads);
307out:
308 mutex_unlock(&smpboot_threads_lock);
309 put_online_cpus();
310 return ret;
311}
312EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread_cpumask);
313
314/**
315 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
316 * @plug_thread: Hotplug thread descriptor
317 *
318 * Stops all threads on all possible cpus.
319 */
320void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
321{
322 get_online_cpus();
323 mutex_lock(&smpboot_threads_lock);
324 list_del(&plug_thread->list);
325 smpboot_destroy_threads(plug_thread);
326 mutex_unlock(&smpboot_threads_lock);
327 put_online_cpus();
328 free_cpumask_var(plug_thread->cpumask);
329}
330EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
331
332/**
333 * smpboot_update_cpumask_percpu_thread - Adjust which per_cpu hotplug threads stay parked
334 * @plug_thread: Hotplug thread descriptor
335 * @new: Revised mask to use
336 *
337 * The cpumask field in the smp_hotplug_thread must not be updated directly
338 * by the client, but only by calling this function.
339 * This function can only be called on a registered smp_hotplug_thread.
340 */
341int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
342 const struct cpumask *new)
343{
344 struct cpumask *old = plug_thread->cpumask;
345 cpumask_var_t tmp;
346 unsigned int cpu;
347
348 if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
349 return -ENOMEM;
350
351 get_online_cpus();
352 mutex_lock(&smpboot_threads_lock);
353
354 /* Park threads that were exclusively enabled on the old mask. */
355 cpumask_andnot(tmp, old, new);
356 for_each_cpu_and(cpu, tmp, cpu_online_mask)
357 smpboot_park_thread(plug_thread, cpu);
358
359 /* Unpark threads that are exclusively enabled on the new mask. */
360 cpumask_andnot(tmp, new, old);
361 for_each_cpu_and(cpu, tmp, cpu_online_mask)
362 smpboot_unpark_thread(plug_thread, cpu);
363
364 cpumask_copy(old, new);
365
366 mutex_unlock(&smpboot_threads_lock);
367 put_online_cpus();
368
369 free_cpumask_var(tmp);
370
371 return 0;
372}
373EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread);
374
375static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
376
377/*
378 * Called to poll specified CPU's state, for example, when waiting for
379 * a CPU to come online.
380 */
381int cpu_report_state(int cpu)
382{
383 return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
384}
385
386/*
387 * If CPU has died properly, set its state to CPU_UP_PREPARE and
388 * return success. Otherwise, return -EBUSY if the CPU died after
389 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
390 * if cpu_wait_death() timed out and the CPU still hasn't gotten around
391 * to dying. In the latter two cases, the CPU might not be set up
392 * properly, but it is up to the arch-specific code to decide.
393 * Finally, -EIO indicates an unanticipated problem.
394 *
395 * Note that it is permissible to omit this call entirely, as is
396 * done in architectures that do no CPU-hotplug error checking.
397 */
398int cpu_check_up_prepare(int cpu)
399{
400 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
401 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
402 return 0;
403 }
404
405 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
406
407 case CPU_POST_DEAD:
408
409 /* The CPU died properly, so just start it up again. */
410 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
411 return 0;
412
413 case CPU_DEAD_FROZEN:
414
415 /*
416 * Timeout during CPU death, so let caller know.
417 * The outgoing CPU completed its processing, but after
418 * cpu_wait_death() timed out and reported the error. The
419 * caller is free to proceed, in which case the state
420 * will be reset properly by cpu_set_state_online().
421 * Proceeding despite this -EBUSY return makes sense
422 * for systems where the outgoing CPUs take themselves
423 * offline, with no post-death manipulation required from
424 * a surviving CPU.
425 */
426 return -EBUSY;
427
428 case CPU_BROKEN:
429
430 /*
431 * The most likely reason we got here is that there was
432 * a timeout during CPU death, and the outgoing CPU never
433 * did complete its processing. This could happen on
434 * a virtualized system if the outgoing VCPU gets preempted
435 * for more than five seconds, and the user attempts to
436 * immediately online that same CPU. Trying again later
437 * might return -EBUSY above, hence -EAGAIN.
438 */
439 return -EAGAIN;
440
441 default:
442
443 /* Should not happen. Famous last words. */
444 return -EIO;
445 }
446}
447
448/*
449 * Mark the specified CPU online.
450 *
451 * Note that it is permissible to omit this call entirely, as is
452 * done in architectures that do no CPU-hotplug error checking.
453 */
454void cpu_set_state_online(int cpu)
455{
456 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
457}
458
459#ifdef CONFIG_HOTPLUG_CPU
460
461/*
462 * Wait for the specified CPU to exit the idle loop and die.
463 */
464bool cpu_wait_death(unsigned int cpu, int seconds)
465{
466 int jf_left = seconds * HZ;
467 int oldstate;
468 bool ret = true;
469 int sleep_jf = 1;
470
471 might_sleep();
472
473 /* The outgoing CPU will normally get done quite quickly. */
474 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
475 goto update_state;
476 udelay(5);
477
478 /* But if the outgoing CPU dawdles, wait increasingly long times. */
479 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
480 schedule_timeout_uninterruptible(sleep_jf);
481 jf_left -= sleep_jf;
482 if (jf_left <= 0)
483 break;
484 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
485 }
486update_state:
487 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
488 if (oldstate == CPU_DEAD) {
489 /* Outgoing CPU died normally, update state. */
490 smp_mb(); /* atomic_read() before update. */
491 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
492 } else {
493 /* Outgoing CPU still hasn't died, set state accordingly. */
494 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
495 oldstate, CPU_BROKEN) != oldstate)
496 goto update_state;
497 ret = false;
498 }
499 return ret;
500}
501
502/*
503 * Called by the outgoing CPU to report its successful death. Return
504 * false if this report follows the surviving CPU's timing out.
505 *
506 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
507 * timed out. This approach allows architectures to omit calls to
508 * cpu_check_up_prepare() and cpu_set_state_online() without defeating
509 * the next cpu_wait_death()'s polling loop.
510 */
511bool cpu_report_death(void)
512{
513 int oldstate;
514 int newstate;
515 int cpu = smp_processor_id();
516
517 do {
518 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
519 if (oldstate != CPU_BROKEN)
520 newstate = CPU_DEAD;
521 else
522 newstate = CPU_DEAD_FROZEN;
523 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
524 oldstate, newstate) != oldstate);
525 return newstate == CPU_DEAD;
526}
527
528#endif /* #ifdef CONFIG_HOTPLUG_CPU */
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 */
28static DEFINE_PER_CPU(struct task_struct *, idle_threads);
29
30struct 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
39void __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 */
50static __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 */
66void __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
81static LIST_HEAD(hotplug_threads);
82static DEFINE_MUTEX(smpboot_threads_lock);
83
84struct smpboot_thread_data {
85 unsigned int cpu;
86 unsigned int status;
87 struct smp_hotplug_thread *ht;
88};
89
90enum {
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 */
106static 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
169static 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(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
213int 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
228static 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
236int 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
247static 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
255int 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
266static 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(tsk);
276 put_task_struct(tsk);
277 *per_cpu_ptr(ht->store, cpu) = NULL;
278 }
279 }
280}
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 */
289int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
290{
291 unsigned int cpu;
292 int ret = 0;
293
294 cpus_read_lock();
295 mutex_lock(&smpboot_threads_lock);
296 for_each_online_cpu(cpu) {
297 ret = __smpboot_create_thread(plug_thread, cpu);
298 if (ret) {
299 smpboot_destroy_threads(plug_thread);
300 goto out;
301 }
302 smpboot_unpark_thread(plug_thread, cpu);
303 }
304 list_add(&plug_thread->list, &hotplug_threads);
305out:
306 mutex_unlock(&smpboot_threads_lock);
307 cpus_read_unlock();
308 return ret;
309}
310EXPORT_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 */
318void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
319{
320 cpus_read_lock();
321 mutex_lock(&smpboot_threads_lock);
322 list_del(&plug_thread->list);
323 smpboot_destroy_threads(plug_thread);
324 mutex_unlock(&smpboot_threads_lock);
325 cpus_read_unlock();
326}
327EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
328
329static 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 */
335int cpu_report_state(int cpu)
336{
337 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 */
352int cpu_check_up_prepare(int cpu)
353{
354 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
355 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 */
415void cpu_set_state_online(int cpu)
416{
417 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
418}
419
420#ifdef CONFIG_HOTPLUG_CPU
421
422/*
423 * Wait for the specified CPU to exit the idle loop and die.
424 */
425bool 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 }
447update_state_early:
448 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
449update_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 */
473bool 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 */