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TOMOYO Linux Cross Reference
Linux/kernel/smpboot.c

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  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         init_idle(tsk, cpu);
 37         return tsk;
 38 }
 39 
 40 void __init idle_thread_set_boot_cpu(void)
 41 {
 42         per_cpu(idle_threads, smp_processor_id()) = current;
 43 }
 44 
 45 /**
 46  * idle_init - Initialize the idle thread for a cpu
 47  * @cpu:        The cpu for which the idle thread should be initialized
 48  *
 49  * Creates the thread if it does not exist.
 50  */
 51 static inline void idle_init(unsigned int cpu)
 52 {
 53         struct task_struct *tsk = per_cpu(idle_threads, cpu);
 54 
 55         if (!tsk) {
 56                 tsk = fork_idle(cpu);
 57                 if (IS_ERR(tsk))
 58                         pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
 59                 else
 60                         per_cpu(idle_threads, cpu) = tsk;
 61         }
 62 }
 63 
 64 /**
 65  * idle_threads_init - Initialize idle threads for all cpus
 66  */
 67 void __init idle_threads_init(void)
 68 {
 69         unsigned int cpu, boot_cpu;
 70 
 71         boot_cpu = smp_processor_id();
 72 
 73         for_each_possible_cpu(cpu) {
 74                 if (cpu != boot_cpu)
 75                         idle_init(cpu);
 76         }
 77 }
 78 #endif
 79 
 80 #endif /* #ifdef CONFIG_SMP */
 81 
 82 static LIST_HEAD(hotplug_threads);
 83 static DEFINE_MUTEX(smpboot_threads_lock);
 84 
 85 struct smpboot_thread_data {
 86         unsigned int                    cpu;
 87         unsigned int                    status;
 88         struct smp_hotplug_thread       *ht;
 89 };
 90 
 91 enum {
 92         HP_THREAD_NONE = 0,
 93         HP_THREAD_ACTIVE,
 94         HP_THREAD_PARKED,
 95 };
 96 
 97 /**
 98  * smpboot_thread_fn - percpu hotplug thread loop function
 99  * @data:       thread data pointer
100  *
101  * Checks for thread stop and park conditions. Calls the necessary
102  * setup, cleanup, park and unpark functions for the registered
103  * thread.
104  *
105  * Returns 1 when the thread should exit, 0 otherwise.
106  */
107 static int smpboot_thread_fn(void *data)
108 {
109         struct smpboot_thread_data *td = data;
110         struct smp_hotplug_thread *ht = td->ht;
111 
112         while (1) {
113                 set_current_state(TASK_INTERRUPTIBLE);
114                 preempt_disable();
115                 if (kthread_should_stop()) {
116                         __set_current_state(TASK_RUNNING);
117                         preempt_enable();
118                         /* cleanup must mirror setup */
119                         if (ht->cleanup && td->status != HP_THREAD_NONE)
120                                 ht->cleanup(td->cpu, cpu_online(td->cpu));
121                         kfree(td);
122                         return 0;
123                 }
124 
125                 if (kthread_should_park()) {
126                         __set_current_state(TASK_RUNNING);
127                         preempt_enable();
128                         if (ht->park && td->status == HP_THREAD_ACTIVE) {
129                                 BUG_ON(td->cpu != smp_processor_id());
130                                 ht->park(td->cpu);
131                                 td->status = HP_THREAD_PARKED;
132                         }
133                         kthread_parkme();
134                         /* We might have been woken for stop */
135                         continue;
136                 }
137 
138                 BUG_ON(td->cpu != smp_processor_id());
139 
140                 /* Check for state change setup */
141                 switch (td->status) {
142                 case HP_THREAD_NONE:
143                         __set_current_state(TASK_RUNNING);
144                         preempt_enable();
145                         if (ht->setup)
146                                 ht->setup(td->cpu);
147                         td->status = HP_THREAD_ACTIVE;
148                         continue;
149 
150                 case HP_THREAD_PARKED:
151                         __set_current_state(TASK_RUNNING);
152                         preempt_enable();
153                         if (ht->unpark)
154                                 ht->unpark(td->cpu);
155                         td->status = HP_THREAD_ACTIVE;
156                         continue;
157                 }
158 
159                 if (!ht->thread_should_run(td->cpu)) {
160                         preempt_enable_no_resched();
161                         schedule();
162                 } else {
163                         __set_current_state(TASK_RUNNING);
164                         preempt_enable();
165                         ht->thread_fn(td->cpu);
166                 }
167         }
168 }
169 
170 static int
171 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
172 {
173         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
174         struct smpboot_thread_data *td;
175 
176         if (tsk)
177                 return 0;
178 
179         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
180         if (!td)
181                 return -ENOMEM;
182         td->cpu = cpu;
183         td->ht = ht;
184 
185         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
186                                     ht->thread_comm);
187         if (IS_ERR(tsk)) {
188                 kfree(td);
189                 return PTR_ERR(tsk);
190         }
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         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                         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         put_online_cpus();
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         get_online_cpus();
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         put_online_cpus();
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 */
483 

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