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path: root/kernel/smpboot.c (plain)
blob: 4a5c6e73ecd41e7107a89b098f4eea9fefc647f1
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 /*
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
211int 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
226static 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
234int 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 if (cpumask_test_cpu(cpu, cur->cpumask))
241 smpboot_unpark_thread(cur, cpu);
242 mutex_unlock(&smpboot_threads_lock);
243 return 0;
244}
245
246static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
247{
248 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
249
250 if (tsk && !ht->selfparking)
251 kthread_park(tsk);
252}
253
254int smpboot_park_threads(unsigned int cpu)
255{
256 struct smp_hotplug_thread *cur;
257
258 mutex_lock(&smpboot_threads_lock);
259 list_for_each_entry_reverse(cur, &hotplug_threads, list)
260 smpboot_park_thread(cur, cpu);
261 mutex_unlock(&smpboot_threads_lock);
262 return 0;
263}
264
265static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
266{
267 unsigned int cpu;
268
269 /* We need to destroy also the parked threads of offline cpus */
270 for_each_possible_cpu(cpu) {
271 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
272
273 if (tsk) {
274 kthread_stop(tsk);
275 put_task_struct(tsk);
276 *per_cpu_ptr(ht->store, cpu) = NULL;
277 }
278 }
279}
280
281/**
282 * smpboot_register_percpu_thread_cpumask - Register a per_cpu thread related
283 * to hotplug
284 * @plug_thread: Hotplug thread descriptor
285 * @cpumask: The cpumask where threads run
286 *
287 * Creates and starts the threads on all online cpus.
288 */
289int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread,
290 const struct cpumask *cpumask)
291{
292 unsigned int cpu;
293 int ret = 0;
294
295 if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
296 return -ENOMEM;
297 cpumask_copy(plug_thread->cpumask, cpumask);
298
299 get_online_cpus();
300 mutex_lock(&smpboot_threads_lock);
301 for_each_online_cpu(cpu) {
302 ret = __smpboot_create_thread(plug_thread, cpu);
303 if (ret) {
304 smpboot_destroy_threads(plug_thread);
305 free_cpumask_var(plug_thread->cpumask);
306 goto out;
307 }
308 if (cpumask_test_cpu(cpu, cpumask))
309 smpboot_unpark_thread(plug_thread, cpu);
310 }
311 list_add(&plug_thread->list, &hotplug_threads);
312out:
313 mutex_unlock(&smpboot_threads_lock);
314 put_online_cpus();
315 return ret;
316}
317EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread_cpumask);
318
319/**
320 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
321 * @plug_thread: Hotplug thread descriptor
322 *
323 * Stops all threads on all possible cpus.
324 */
325void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
326{
327 get_online_cpus();
328 mutex_lock(&smpboot_threads_lock);
329 list_del(&plug_thread->list);
330 smpboot_destroy_threads(plug_thread);
331 mutex_unlock(&smpboot_threads_lock);
332 put_online_cpus();
333 free_cpumask_var(plug_thread->cpumask);
334}
335EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
336
337/**
338 * smpboot_update_cpumask_percpu_thread - Adjust which per_cpu hotplug threads stay parked
339 * @plug_thread: Hotplug thread descriptor
340 * @new: Revised mask to use
341 *
342 * The cpumask field in the smp_hotplug_thread must not be updated directly
343 * by the client, but only by calling this function.
344 * This function can only be called on a registered smp_hotplug_thread.
345 */
346int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
347 const struct cpumask *new)
348{
349 struct cpumask *old = plug_thread->cpumask;
350 cpumask_var_t tmp;
351 unsigned int cpu;
352
353 if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
354 return -ENOMEM;
355
356 get_online_cpus();
357 mutex_lock(&smpboot_threads_lock);
358
359 /* Park threads that were exclusively enabled on the old mask. */
360 cpumask_andnot(tmp, old, new);
361 for_each_cpu_and(cpu, tmp, cpu_online_mask)
362 smpboot_park_thread(plug_thread, cpu);
363
364 /* Unpark threads that are exclusively enabled on the new mask. */
365 cpumask_andnot(tmp, new, old);
366 for_each_cpu_and(cpu, tmp, cpu_online_mask)
367 smpboot_unpark_thread(plug_thread, cpu);
368
369 cpumask_copy(old, new);
370
371 mutex_unlock(&smpboot_threads_lock);
372 put_online_cpus();
373
374 free_cpumask_var(tmp);
375
376 return 0;
377}
378EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread);
379
380static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
381
382/*
383 * Called to poll specified CPU's state, for example, when waiting for
384 * a CPU to come online.
385 */
386int cpu_report_state(int cpu)
387{
388 return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
389}
390
391/*
392 * If CPU has died properly, set its state to CPU_UP_PREPARE and
393 * return success. Otherwise, return -EBUSY if the CPU died after
394 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
395 * if cpu_wait_death() timed out and the CPU still hasn't gotten around
396 * to dying. In the latter two cases, the CPU might not be set up
397 * properly, but it is up to the arch-specific code to decide.
398 * Finally, -EIO indicates an unanticipated problem.
399 *
400 * Note that it is permissible to omit this call entirely, as is
401 * done in architectures that do no CPU-hotplug error checking.
402 */
403int cpu_check_up_prepare(int cpu)
404{
405 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
406 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
407 return 0;
408 }
409
410 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
411
412 case CPU_POST_DEAD:
413
414 /* The CPU died properly, so just start it up again. */
415 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
416 return 0;
417
418 case CPU_DEAD_FROZEN:
419
420 /*
421 * Timeout during CPU death, so let caller know.
422 * The outgoing CPU completed its processing, but after
423 * cpu_wait_death() timed out and reported the error. The
424 * caller is free to proceed, in which case the state
425 * will be reset properly by cpu_set_state_online().
426 * Proceeding despite this -EBUSY return makes sense
427 * for systems where the outgoing CPUs take themselves
428 * offline, with no post-death manipulation required from
429 * a surviving CPU.
430 */
431 return -EBUSY;
432
433 case CPU_BROKEN:
434
435 /*
436 * The most likely reason we got here is that there was
437 * a timeout during CPU death, and the outgoing CPU never
438 * did complete its processing. This could happen on
439 * a virtualized system if the outgoing VCPU gets preempted
440 * for more than five seconds, and the user attempts to
441 * immediately online that same CPU. Trying again later
442 * might return -EBUSY above, hence -EAGAIN.
443 */
444 return -EAGAIN;
445
446 default:
447
448 /* Should not happen. Famous last words. */
449 return -EIO;
450 }
451}
452
453/*
454 * Mark the specified CPU online.
455 *
456 * Note that it is permissible to omit this call entirely, as is
457 * done in architectures that do no CPU-hotplug error checking.
458 */
459void cpu_set_state_online(int cpu)
460{
461 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
462}
463
464#ifdef CONFIG_HOTPLUG_CPU
465
466/*
467 * Wait for the specified CPU to exit the idle loop and die.
468 */
469bool cpu_wait_death(unsigned int cpu, int seconds)
470{
471 int jf_left = seconds * HZ;
472 int oldstate;
473 bool ret = true;
474 int sleep_jf = 1;
475
476 might_sleep();
477
478 /* The outgoing CPU will normally get done quite quickly. */
479 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
480 goto update_state;
481 udelay(5);
482
483 /* But if the outgoing CPU dawdles, wait increasingly long times. */
484 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
485 schedule_timeout_uninterruptible(sleep_jf);
486 jf_left -= sleep_jf;
487 if (jf_left <= 0)
488 break;
489 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
490 }
491update_state:
492 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
493 if (oldstate == CPU_DEAD) {
494 /* Outgoing CPU died normally, update state. */
495 smp_mb(); /* atomic_read() before update. */
496 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
497 } else {
498 /* Outgoing CPU still hasn't died, set state accordingly. */
499 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
500 oldstate, CPU_BROKEN) != oldstate)
501 goto update_state;
502 ret = false;
503 }
504 return ret;
505}
506
507/*
508 * Called by the outgoing CPU to report its successful death. Return
509 * false if this report follows the surviving CPU's timing out.
510 *
511 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
512 * timed out. This approach allows architectures to omit calls to
513 * cpu_check_up_prepare() and cpu_set_state_online() without defeating
514 * the next cpu_wait_death()'s polling loop.
515 */
516bool cpu_report_death(void)
517{
518 int oldstate;
519 int newstate;
520 int cpu = smp_processor_id();
521
522 do {
523 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
524 if (oldstate != CPU_BROKEN)
525 newstate = CPU_DEAD;
526 else
527 newstate = CPU_DEAD_FROZEN;
528 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
529 oldstate, newstate) != oldstate);
530 return newstate == CPU_DEAD;
531}
532
533#endif /* #ifdef CONFIG_HOTPLUG_CPU */
534
generated by cgit at 2024-05-18 17:29:15 (GMT)