Line data    Source code

       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           1 : static int smpboot_thread_fn(void *data)
     107             : {
     108           1 :         struct smpboot_thread_data *td = data;
     109           1 :         struct smp_hotplug_thread *ht = td->ht;
     110             : 
     111             :         while (1) {
     112         320 :                 set_current_state(TASK_INTERRUPTIBLE);
     113         320 :                 preempt_disable();
     114         320 :                 if (kthread_should_stop()) {
     115           0 :                         __set_current_state(TASK_RUNNING);
     116           0 :                         preempt_enable();
     117             :                         /* cleanup must mirror setup */
     118           0 :                         if (ht->cleanup && td->status != HP_THREAD_NONE)
     119           0 :                                 ht->cleanup(td->cpu, cpu_online(td->cpu));
     120           0 :                         kfree(td);
     121           0 :                         return 0;
     122             :                 }
     123             : 
     124         320 :                 if (kthread_should_park()) {
     125           0 :                         __set_current_state(TASK_RUNNING);
     126           0 :                         preempt_enable();
     127           0 :                         if (ht->park && td->status == HP_THREAD_ACTIVE) {
     128           0 :                                 BUG_ON(td->cpu != smp_processor_id());
     129           0 :                                 ht->park(td->cpu);
     130           0 :                                 td->status = HP_THREAD_PARKED;
     131             :                         }
     132           0 :                         kthread_parkme();
     133             :                         /* We might have been woken for stop */
     134           0 :                         continue;
     135             :                 }
     136             : 
     137         320 :                 BUG_ON(td->cpu != smp_processor_id());
     138             : 
     139             :                 /* Check for state change setup */
     140         320 :                 switch (td->status) {
     141             :                 case HP_THREAD_NONE:
     142           1 :                         __set_current_state(TASK_RUNNING);
     143           1 :                         preempt_enable();
     144           1 :                         if (ht->setup)
     145           0 :                                 ht->setup(td->cpu);
     146           1 :                         td->status = HP_THREAD_ACTIVE;
     147           1 :                         continue;
     148             : 
     149             :                 case HP_THREAD_PARKED:
     150           0 :                         __set_current_state(TASK_RUNNING);
     151           0 :                         preempt_enable();
     152           0 :                         if (ht->unpark)
     153           0 :                                 ht->unpark(td->cpu);
     154           0 :                         td->status = HP_THREAD_ACTIVE;
     155           0 :                         continue;
     156             :                 }
     157             : 
     158         319 :                 if (!ht->thread_should_run(td->cpu)) {
     159         160 :                         preempt_enable_no_resched();
     160         160 :                         schedule();
     161             :                 } else {
     162         159 :                         __set_current_state(TASK_RUNNING);
     163         159 :                         preempt_enable();
     164         159 :                         ht->thread_fn(td->cpu);
     165             :                 }
     166             :         }
     167             : }
     168             : 
     169             : static int
     170           1 : __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
     171             : {
     172           1 :         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
     173             :         struct smpboot_thread_data *td;
     174             : 
     175           1 :         if (tsk)
     176             :                 return 0;
     177             : 
     178           1 :         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
     179           1 :         if (!td)
     180             :                 return -ENOMEM;
     181           1 :         td->cpu = cpu;
     182           1 :         td->ht = ht;
     183             : 
     184           1 :         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
     185             :                                     ht->thread_comm);
     186           1 :         if (IS_ERR(tsk)) {
     187           0 :                 kfree(td);
     188           0 :                 return PTR_ERR(tsk);
     189             :         }
     190           1 :         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           1 :         kthread_park(tsk);
     196           1 :         get_task_struct(tsk);
     197           1 :         *per_cpu_ptr(ht->store, cpu) = tsk;
     198           1 :         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           0 :                 if (!wait_task_inactive(tsk, TASK_PARKED))
     206           0 :                         WARN_ON(1);
     207             :                 else
     208           0 :                         ht->create(cpu);
     209             :         }
     210             :         return 0;
     211             : }
     212             : 
     213           0 : int smpboot_create_threads(unsigned int cpu)
     214             : {
     215             :         struct smp_hotplug_thread *cur;
     216           0 :         int ret = 0;
     217             : 
     218           0 :         mutex_lock(&smpboot_threads_lock);
     219           0 :         list_for_each_entry(cur, &hotplug_threads, list) {
     220           0 :                 ret = __smpboot_create_thread(cur, cpu);
     221           0 :                 if (ret)
     222             :                         break;
     223             :         }
     224           0 :         mutex_unlock(&smpboot_threads_lock);
     225           0 :         return ret;
     226             : }
     227             : 
     228             : static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
     229             : {
     230           1 :         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
     231             : 
     232           1 :         if (!ht->selfparking)
     233           1 :                 kthread_unpark(tsk);
     234             : }
     235             : 
     236           0 : int smpboot_unpark_threads(unsigned int cpu)
     237             : {
     238             :         struct smp_hotplug_thread *cur;
     239             : 
     240           0 :         mutex_lock(&smpboot_threads_lock);
     241           0 :         list_for_each_entry(cur, &hotplug_threads, list)
     242           0 :                 smpboot_unpark_thread(cur, cpu);
     243           0 :         mutex_unlock(&smpboot_threads_lock);
     244           0 :         return 0;
     245             : }
     246             : 
     247             : static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
     248             : {
     249           0 :         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
     250             : 
     251           0 :         if (tsk && !ht->selfparking)
     252           0 :                 kthread_park(tsk);
     253             : }
     254             : 
     255           0 : int smpboot_park_threads(unsigned int cpu)
     256             : {
     257             :         struct smp_hotplug_thread *cur;
     258             : 
     259           0 :         mutex_lock(&smpboot_threads_lock);
     260           0 :         list_for_each_entry_reverse(cur, &hotplug_threads, list)
     261           0 :                 smpboot_park_thread(cur, cpu);
     262           0 :         mutex_unlock(&smpboot_threads_lock);
     263           0 :         return 0;
     264             : }
     265             : 
     266           0 : 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           0 :         for_each_possible_cpu(cpu) {
     272           0 :                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
     273             : 
     274           0 :                 if (tsk) {
     275           0 :                         kthread_stop(tsk);
     276           0 :                         put_task_struct(tsk);
     277           0 :                         *per_cpu_ptr(ht->store, cpu) = NULL;
     278             :                 }
     279             :         }
     280           0 : }
     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           1 : int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
     290             : {
     291             :         unsigned int cpu;
     292           1 :         int ret = 0;
     293             : 
     294             :         cpus_read_lock();
     295           1 :         mutex_lock(&smpboot_threads_lock);
     296           2 :         for_each_online_cpu(cpu) {
     297           1 :                 ret = __smpboot_create_thread(plug_thread, cpu);
     298           1 :                 if (ret) {
     299           0 :                         smpboot_destroy_threads(plug_thread);
     300           0 :                         goto out;
     301             :                 }
     302           2 :                 smpboot_unpark_thread(plug_thread, cpu);
     303             :         }
     304           1 :         list_add(&plug_thread->list, &hotplug_threads);
     305             : out:
     306           1 :         mutex_unlock(&smpboot_threads_lock);
     307             :         cpus_read_unlock();
     308           1 :         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           0 : void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
     319             : {
     320             :         cpus_read_lock();
     321           0 :         mutex_lock(&smpboot_threads_lock);
     322           0 :         list_del(&plug_thread->list);
     323           0 :         smpboot_destroy_threads(plug_thread);
     324           0 :         mutex_unlock(&smpboot_threads_lock);
     325             :         cpus_read_unlock();
     326           0 : }
     327             : EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);