Merge drm/drm-next into drm-intel-gt-next
[linux-2.6-microblaze.git] / kernel / smpboot.c
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 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         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
213 int 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
228 static 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
236 int 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
247 static 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
255 int 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
266 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         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  */
289 int 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);
305 out:
306         mutex_unlock(&smpboot_threads_lock);
307         cpus_read_unlock();
308         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 void 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 }
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 int 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  */
352 int 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         default:
396
397                 /* Should not happen.  Famous last words. */
398                 return -EIO;
399         }
400 }
401
402 /*
403  * Mark the specified CPU online.
404  *
405  * Note that it is permissible to omit this call entirely, as is
406  * done in architectures that do no CPU-hotplug error checking.
407  */
408 void cpu_set_state_online(int cpu)
409 {
410         (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
411 }
412
413 #ifdef CONFIG_HOTPLUG_CPU
414
415 /*
416  * Wait for the specified CPU to exit the idle loop and die.
417  */
418 bool cpu_wait_death(unsigned int cpu, int seconds)
419 {
420         int jf_left = seconds * HZ;
421         int oldstate;
422         bool ret = true;
423         int sleep_jf = 1;
424
425         might_sleep();
426
427         /* The outgoing CPU will normally get done quite quickly. */
428         if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
429                 goto update_state;
430         udelay(5);
431
432         /* But if the outgoing CPU dawdles, wait increasingly long times. */
433         while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
434                 schedule_timeout_uninterruptible(sleep_jf);
435                 jf_left -= sleep_jf;
436                 if (jf_left <= 0)
437                         break;
438                 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
439         }
440 update_state:
441         oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
442         if (oldstate == CPU_DEAD) {
443                 /* Outgoing CPU died normally, update state. */
444                 smp_mb(); /* atomic_read() before update. */
445                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
446         } else {
447                 /* Outgoing CPU still hasn't died, set state accordingly. */
448                 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
449                                    oldstate, CPU_BROKEN) != oldstate)
450                         goto update_state;
451                 ret = false;
452         }
453         return ret;
454 }
455
456 /*
457  * Called by the outgoing CPU to report its successful death.  Return
458  * false if this report follows the surviving CPU's timing out.
459  *
460  * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
461  * timed out.  This approach allows architectures to omit calls to
462  * cpu_check_up_prepare() and cpu_set_state_online() without defeating
463  * the next cpu_wait_death()'s polling loop.
464  */
465 bool cpu_report_death(void)
466 {
467         int oldstate;
468         int newstate;
469         int cpu = smp_processor_id();
470
471         do {
472                 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
473                 if (oldstate != CPU_BROKEN)
474                         newstate = CPU_DEAD;
475                 else
476                         newstate = CPU_DEAD_FROZEN;
477         } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
478                                 oldstate, newstate) != oldstate);
479         return newstate == CPU_DEAD;
480 }
481
482 #endif /* #ifdef CONFIG_HOTPLUG_CPU */