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Linux/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/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  */
 26 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
 27 
 28 struct 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 
 38 void __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  */
 49 static 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  */
 65 void __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 
 80 static LIST_HEAD(hotplug_threads);
 81 static DEFINE_MUTEX(smpboot_threads_lock);
 82 
 83 struct smpboot_thread_data {
 84         unsigned int                    cpu;
 85         unsigned int                    status;
 86         struct smp_hotplug_thread       *ht;
 87 };
 88 
 89 enum {
 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  */
105 static 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 
168 static 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 
211 int 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 
226 static 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 
234 int 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 
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_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  */
289 int 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);
312 out:
313         mutex_unlock(&smpboot_threads_lock);
314         put_online_cpus();
315         return ret;
316 }
317 EXPORT_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  */
325 void 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 }
335 EXPORT_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  */
346 int 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 }
378 EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread);
379 
380 static 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  */
386 int 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  */
403 int 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  */
459 void 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  */
469 bool 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         }
491 update_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  */
516 bool 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 

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