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/sched/task.h>
13 #include <linux/export.h>
14 #include <linux/percpu.h>
15 #include <linux/kthread.h>
16 #include <linux/smpboot.h>
17
18 #include "smpboot.h"
19
20 #ifdef CONFIG_SMP
21
22 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
23 /*
24 * For the hotplug case we keep the task structs around and reuse
25 * them.
26 */
27 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
28
idle_thread_get(unsigned int cpu)29 struct task_struct *idle_thread_get(unsigned int cpu)
30 {
31 struct task_struct *tsk = per_cpu(idle_threads, cpu);
32
33 if (!tsk)
34 return ERR_PTR(-ENOMEM);
35 init_idle(tsk, cpu);
36 return tsk;
37 }
38
idle_thread_set_boot_cpu(void)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 */
idle_init(unsigned int cpu)50 static 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 */
idle_threads_init(void)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 */
smpboot_thread_fn(void * data)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(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
169 static int
__smpboot_create_thread(struct smp_hotplug_thread * ht,unsigned int cpu)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 /*
191 * Park the thread so that it could start right on the CPU
192 * when it is available.
193 */
194 kthread_park(tsk);
195 get_task_struct(tsk);
196 *per_cpu_ptr(ht->store, cpu) = tsk;
197 if (ht->create) {
198 /*
199 * Make sure that the task has actually scheduled out
200 * into park position, before calling the create
201 * callback. At least the migration thread callback
202 * requires that the task is off the runqueue.
203 */
204 if (!wait_task_inactive(tsk, TASK_PARKED))
205 WARN_ON(1);
206 else
207 ht->create(cpu);
208 }
209 return 0;
210 }
211
smpboot_create_threads(unsigned int cpu)212 int smpboot_create_threads(unsigned int cpu)
213 {
214 struct smp_hotplug_thread *cur;
215 int ret = 0;
216
217 mutex_lock(&smpboot_threads_lock);
218 list_for_each_entry(cur, &hotplug_threads, list) {
219 ret = __smpboot_create_thread(cur, cpu);
220 if (ret)
221 break;
222 }
223 mutex_unlock(&smpboot_threads_lock);
224 return ret;
225 }
226
smpboot_unpark_thread(struct smp_hotplug_thread * ht,unsigned int cpu)227 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
228 {
229 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
230
231 if (!ht->selfparking)
232 kthread_unpark(tsk);
233 }
234
smpboot_unpark_threads(unsigned int cpu)235 int smpboot_unpark_threads(unsigned int cpu)
236 {
237 struct smp_hotplug_thread *cur;
238
239 mutex_lock(&smpboot_threads_lock);
240 list_for_each_entry(cur, &hotplug_threads, list)
241 smpboot_unpark_thread(cur, cpu);
242 mutex_unlock(&smpboot_threads_lock);
243 return 0;
244 }
245
smpboot_park_thread(struct smp_hotplug_thread * ht,unsigned int cpu)246 static 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
smpboot_park_threads(unsigned int cpu)254 int 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
smpboot_destroy_threads(struct smp_hotplug_thread * ht)265 static 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 - 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 */
smpboot_register_percpu_thread(struct smp_hotplug_thread * plug_thread)288 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
289 {
290 unsigned int cpu;
291 int ret = 0;
292
293 get_online_cpus();
294 mutex_lock(&smpboot_threads_lock);
295 for_each_online_cpu(cpu) {
296 ret = __smpboot_create_thread(plug_thread, cpu);
297 if (ret) {
298 smpboot_destroy_threads(plug_thread);
299 goto out;
300 }
301 smpboot_unpark_thread(plug_thread, cpu);
302 }
303 list_add(&plug_thread->list, &hotplug_threads);
304 out:
305 mutex_unlock(&smpboot_threads_lock);
306 put_online_cpus();
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 */
smpboot_unregister_percpu_thread(struct smp_hotplug_thread * plug_thread)317 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
318 {
319 get_online_cpus();
320 mutex_lock(&smpboot_threads_lock);
321 list_del(&plug_thread->list);
322 smpboot_destroy_threads(plug_thread);
323 mutex_unlock(&smpboot_threads_lock);
324 put_online_cpus();
325 }
326 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
327
328 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
329
330 /*
331 * Called to poll specified CPU's state, for example, when waiting for
332 * a CPU to come online.
333 */
cpu_report_state(int cpu)334 int cpu_report_state(int cpu)
335 {
336 return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
337 }
338
339 /*
340 * If CPU has died properly, set its state to CPU_UP_PREPARE and
341 * return success. Otherwise, return -EBUSY if the CPU died after
342 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
343 * if cpu_wait_death() timed out and the CPU still hasn't gotten around
344 * to dying. In the latter two cases, the CPU might not be set up
345 * properly, but it is up to the arch-specific code to decide.
346 * Finally, -EIO indicates an unanticipated problem.
347 *
348 * Note that it is permissible to omit this call entirely, as is
349 * done in architectures that do no CPU-hotplug error checking.
350 */
cpu_check_up_prepare(int cpu)351 int cpu_check_up_prepare(int cpu)
352 {
353 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
354 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
355 return 0;
356 }
357
358 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
359
360 case CPU_POST_DEAD:
361
362 /* The CPU died properly, so just start it up again. */
363 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
364 return 0;
365
366 case CPU_DEAD_FROZEN:
367
368 /*
369 * Timeout during CPU death, so let caller know.
370 * The outgoing CPU completed its processing, but after
371 * cpu_wait_death() timed out and reported the error. The
372 * caller is free to proceed, in which case the state
373 * will be reset properly by cpu_set_state_online().
374 * Proceeding despite this -EBUSY return makes sense
375 * for systems where the outgoing CPUs take themselves
376 * offline, with no post-death manipulation required from
377 * a surviving CPU.
378 */
379 return -EBUSY;
380
381 case CPU_BROKEN:
382
383 /*
384 * The most likely reason we got here is that there was
385 * a timeout during CPU death, and the outgoing CPU never
386 * did complete its processing. This could happen on
387 * a virtualized system if the outgoing VCPU gets preempted
388 * for more than five seconds, and the user attempts to
389 * immediately online that same CPU. Trying again later
390 * might return -EBUSY above, hence -EAGAIN.
391 */
392 return -EAGAIN;
393
394 default:
395
396 /* Should not happen. Famous last words. */
397 return -EIO;
398 }
399 }
400
401 /*
402 * Mark the specified CPU online.
403 *
404 * Note that it is permissible to omit this call entirely, as is
405 * done in architectures that do no CPU-hotplug error checking.
406 */
cpu_set_state_online(int cpu)407 void cpu_set_state_online(int cpu)
408 {
409 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
410 }
411
412 #ifdef CONFIG_HOTPLUG_CPU
413
414 /*
415 * Wait for the specified CPU to exit the idle loop and die.
416 */
cpu_wait_death(unsigned int cpu,int seconds)417 bool cpu_wait_death(unsigned int cpu, int seconds)
418 {
419 int jf_left = seconds * HZ;
420 int oldstate;
421 bool ret = true;
422 int sleep_jf = 1;
423
424 might_sleep();
425
426 /* The outgoing CPU will normally get done quite quickly. */
427 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
428 goto update_state;
429 udelay(5);
430
431 /* But if the outgoing CPU dawdles, wait increasingly long times. */
432 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
433 schedule_timeout_uninterruptible(sleep_jf);
434 jf_left -= sleep_jf;
435 if (jf_left <= 0)
436 break;
437 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
438 }
439 update_state:
440 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
441 if (oldstate == CPU_DEAD) {
442 /* Outgoing CPU died normally, update state. */
443 smp_mb(); /* atomic_read() before update. */
444 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
445 } else {
446 /* Outgoing CPU still hasn't died, set state accordingly. */
447 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
448 oldstate, CPU_BROKEN) != oldstate)
449 goto update_state;
450 ret = false;
451 }
452 return ret;
453 }
454
455 /*
456 * Called by the outgoing CPU to report its successful death. Return
457 * false if this report follows the surviving CPU's timing out.
458 *
459 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
460 * timed out. This approach allows architectures to omit calls to
461 * cpu_check_up_prepare() and cpu_set_state_online() without defeating
462 * the next cpu_wait_death()'s polling loop.
463 */
cpu_report_death(void)464 bool cpu_report_death(void)
465 {
466 int oldstate;
467 int newstate;
468 int cpu = smp_processor_id();
469
470 do {
471 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
472 if (oldstate != CPU_BROKEN)
473 newstate = CPU_DEAD;
474 else
475 newstate = CPU_DEAD_FROZEN;
476 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
477 oldstate, newstate) != oldstate);
478 return newstate == CPU_DEAD;
479 }
480
481 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
482
