~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/smpboot.c

Version: ~ [ linux-5.14-rc1 ] ~ [ linux-5.13.1 ] ~ [ linux-5.12.16 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.49 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.131 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.197 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.239 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.275 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.275 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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                 if (cpumask_test_cpu(cpu, cur->cpumask))
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_cpumask - Register a per_cpu thread related
284  *                                          to hotplug
285  * @plug_thread:        Hotplug thread descriptor
286  * @cpumask:            The cpumask where threads run
287  *
288  * Creates and starts the threads on all online cpus.
289  */
290 int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread,
291                                            const struct cpumask *cpumask)
292 {
293         unsigned int cpu;
294         int ret = 0;
295 
296         if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL))
297                 return -ENOMEM;
298         cpumask_copy(plug_thread->cpumask, cpumask);
299 
300         get_online_cpus();
301         mutex_lock(&smpboot_threads_lock);
302         for_each_online_cpu(cpu) {
303                 ret = __smpboot_create_thread(plug_thread, cpu);
304                 if (ret) {
305                         smpboot_destroy_threads(plug_thread);
306                         free_cpumask_var(plug_thread->cpumask);
307                         goto out;
308                 }
309                 if (cpumask_test_cpu(cpu, cpumask))
310                         smpboot_unpark_thread(plug_thread, cpu);
311         }
312         list_add(&plug_thread->list, &hotplug_threads);
313 out:
314         mutex_unlock(&smpboot_threads_lock);
315         put_online_cpus();
316         return ret;
317 }
318 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread_cpumask);
319 
320 /**
321  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
322  * @plug_thread:        Hotplug thread descriptor
323  *
324  * Stops all threads on all possible cpus.
325  */
326 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
327 {
328         get_online_cpus();
329         mutex_lock(&smpboot_threads_lock);
330         list_del(&plug_thread->list);
331         smpboot_destroy_threads(plug_thread);
332         mutex_unlock(&smpboot_threads_lock);
333         put_online_cpus();
334         free_cpumask_var(plug_thread->cpumask);
335 }
336 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
337 
338 /**
339  * smpboot_update_cpumask_percpu_thread - Adjust which per_cpu hotplug threads stay parked
340  * @plug_thread:        Hotplug thread descriptor
341  * @new:                Revised mask to use
342  *
343  * The cpumask field in the smp_hotplug_thread must not be updated directly
344  * by the client, but only by calling this function.
345  * This function can only be called on a registered smp_hotplug_thread.
346  */
347 void smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread,
348                                           const struct cpumask *new)
349 {
350         struct cpumask *old = plug_thread->cpumask;
351         static struct cpumask tmp;
352         unsigned int cpu;
353 
354         lockdep_assert_cpus_held();
355         mutex_lock(&smpboot_threads_lock);
356 
357         /* Park threads that were exclusively enabled on the old mask. */
358         cpumask_andnot(&tmp, old, new);
359         for_each_cpu_and(cpu, &tmp, cpu_online_mask)
360                 smpboot_park_thread(plug_thread, cpu);
361 
362         /* Unpark threads that are exclusively enabled on the new mask. */
363         cpumask_andnot(&tmp, new, old);
364         for_each_cpu_and(cpu, &tmp, cpu_online_mask)
365                 smpboot_unpark_thread(plug_thread, cpu);
366 
367         cpumask_copy(old, new);
368 
369         mutex_unlock(&smpboot_threads_lock);
370 }
371 
372 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
373 
374 /*
375  * Called to poll specified CPU's state, for example, when waiting for
376  * a CPU to come online.
377  */
378 int cpu_report_state(int cpu)
379 {
380         return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
381 }
382 
383 /*
384  * If CPU has died properly, set its state to CPU_UP_PREPARE and
385  * return success.  Otherwise, return -EBUSY if the CPU died after
386  * cpu_wait_death() timed out.  And yet otherwise again, return -EAGAIN
387  * if cpu_wait_death() timed out and the CPU still hasn't gotten around
388  * to dying.  In the latter two cases, the CPU might not be set up
389  * properly, but it is up to the arch-specific code to decide.
390  * Finally, -EIO indicates an unanticipated problem.
391  *
392  * Note that it is permissible to omit this call entirely, as is
393  * done in architectures that do no CPU-hotplug error checking.
394  */
395 int cpu_check_up_prepare(int cpu)
396 {
397         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
398                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
399                 return 0;
400         }
401 
402         switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
403 
404         case CPU_POST_DEAD:
405 
406                 /* The CPU died properly, so just start it up again. */
407                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
408                 return 0;
409 
410         case CPU_DEAD_FROZEN:
411 
412                 /*
413                  * Timeout during CPU death, so let caller know.
414                  * The outgoing CPU completed its processing, but after
415                  * cpu_wait_death() timed out and reported the error. The
416                  * caller is free to proceed, in which case the state
417                  * will be reset properly by cpu_set_state_online().
418                  * Proceeding despite this -EBUSY return makes sense
419                  * for systems where the outgoing CPUs take themselves
420                  * offline, with no post-death manipulation required from
421                  * a surviving CPU.
422                  */
423                 return -EBUSY;
424 
425         case CPU_BROKEN:
426 
427                 /*
428                  * The most likely reason we got here is that there was
429                  * a timeout during CPU death, and the outgoing CPU never
430                  * did complete its processing.  This could happen on
431                  * a virtualized system if the outgoing VCPU gets preempted
432                  * for more than five seconds, and the user attempts to
433                  * immediately online that same CPU.  Trying again later
434                  * might return -EBUSY above, hence -EAGAIN.
435                  */
436                 return -EAGAIN;
437 
438         default:
439 
440                 /* Should not happen.  Famous last words. */
441                 return -EIO;
442         }
443 }
444 
445 /*
446  * Mark the specified CPU online.
447  *
448  * Note that it is permissible to omit this call entirely, as is
449  * done in architectures that do no CPU-hotplug error checking.
450  */
451 void cpu_set_state_online(int cpu)
452 {
453         (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
454 }
455 
456 #ifdef CONFIG_HOTPLUG_CPU
457 
458 /*
459  * Wait for the specified CPU to exit the idle loop and die.
460  */
461 bool cpu_wait_death(unsigned int cpu, int seconds)
462 {
463         int jf_left = seconds * HZ;
464         int oldstate;
465         bool ret = true;
466         int sleep_jf = 1;
467 
468         might_sleep();
469 
470         /* The outgoing CPU will normally get done quite quickly. */
471         if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
472                 goto update_state;
473         udelay(5);
474 
475         /* But if the outgoing CPU dawdles, wait increasingly long times. */
476         while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
477                 schedule_timeout_uninterruptible(sleep_jf);
478                 jf_left -= sleep_jf;
479                 if (jf_left <= 0)
480                         break;
481                 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
482         }
483 update_state:
484         oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
485         if (oldstate == CPU_DEAD) {
486                 /* Outgoing CPU died normally, update state. */
487                 smp_mb(); /* atomic_read() before update. */
488                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
489         } else {
490                 /* Outgoing CPU still hasn't died, set state accordingly. */
491                 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
492                                    oldstate, CPU_BROKEN) != oldstate)
493                         goto update_state;
494                 ret = false;
495         }
496         return ret;
497 }
498 
499 /*
500  * Called by the outgoing CPU to report its successful death.  Return
501  * false if this report follows the surviving CPU's timing out.
502  *
503  * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
504  * timed out.  This approach allows architectures to omit calls to
505  * cpu_check_up_prepare() and cpu_set_state_online() without defeating
506  * the next cpu_wait_death()'s polling loop.
507  */
508 bool cpu_report_death(void)
509 {
510         int oldstate;
511         int newstate;
512         int cpu = smp_processor_id();
513 
514         do {
515                 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
516                 if (oldstate != CPU_BROKEN)
517                         newstate = CPU_DEAD;
518                 else
519                         newstate = CPU_DEAD_FROZEN;
520         } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
521                                 oldstate, newstate) != oldstate);
522         return newstate == CPU_DEAD;
523 }
524 
525 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
526 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp