Linux 5.2-rc6
[sfrench/cifs-2.6.git] / kernel / smpboot.c
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
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
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 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 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
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
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
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
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
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
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
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  */
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  */
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  */
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  */
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  */
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  */
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  */
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 */