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/init.h>
   8 #include <linux/list.h>
   9 #include <linux/slab.h>
  10 #include <linux/sched.h>
  11 #include <linux/export.h>
  12 #include <linux/percpu.h>
  13 #include <linux/kthread.h>
  14 #include <linux/smpboot.h>
  15
  16 #include "smpboot.h"
  17
  18 #ifdef CONFIG_SMP
  19
  20 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
  21 /*
  22  * For the hotplug case we keep the task structs around and reuse
  23  * them.
  24  */
  25 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
  26
  27 struct task_struct *idle_thread_get(unsigned int cpu)
  28 {
  29         struct task_struct *tsk = per_cpu(idle_threads, cpu);
  30
  31         if (!tsk)
  32                 return ERR_PTR(-ENOMEM);
  33         init_idle(tsk, cpu);
  34         return tsk;
  35 }
  36
  37 void __init idle_thread_set_boot_cpu(void)
  38 {
  39         per_cpu(idle_threads, smp_processor_id()) = current;
  40 }
  41
  42 /**
  43  * idle_init - Initialize the idle thread for a cpu
  44  * @cpu:        The cpu for which the idle thread should be initialized
  45  *
  46  * Creates the thread if it does not exist.
  47  */
  48 static inline void idle_init(unsigned int cpu)
  49 {
  50         struct task_struct *tsk = per_cpu(idle_threads, cpu);
  51
  52         if (!tsk) {
  53                 tsk = fork_idle(cpu);
  54                 if (IS_ERR(tsk))
  55                         pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
  56                 else
  57                         per_cpu(idle_threads, cpu) = tsk;
  58         }
  59 }
  60
  61 /**
  62  * idle_threads_init - Initialize idle threads for all cpus
  63  */
  64 void __init idle_threads_init(void)
  65 {
  66         unsigned int cpu, boot_cpu;
  67
  68         boot_cpu = smp_processor_id();
  69
  70         for_each_possible_cpu(cpu) {
  71                 if (cpu != boot_cpu)
  72                         idle_init(cpu);
  73         }
  74 }
  75 #endif
  76
  77 #endif /* #ifdef CONFIG_SMP */
  78
  79 static LIST_HEAD(hotplug_threads);
  80 static DEFINE_MUTEX(smpboot_threads_lock);
  81
  82 struct smpboot_thread_data {
  83         unsigned int                    cpu;
  84         unsigned int                    status;
  85         struct smp_hotplug_thread       *ht;
  86 };
  87
  88 enum {
  89         HP_THREAD_NONE = 0,
  90         HP_THREAD_ACTIVE,
  91         HP_THREAD_PARKED,
  92 };
  93
  94 /**
  95  * smpboot_thread_fn - percpu hotplug thread loop function
  96  * @data:       thread data pointer
  97  *
  98  * Checks for thread stop and park conditions. Calls the necessary
  99  * setup, cleanup, park and unpark functions for the registered
 100  * thread.
 101  *
 102  * Returns 1 when the thread should exit, 0 otherwise.
 103  */
 104 static int smpboot_thread_fn(void *data)
 105 {
 106         struct smpboot_thread_data *td = data;
 107         struct smp_hotplug_thread *ht = td->ht;
 108
 109         while (1) {
 110                 set_current_state(TASK_INTERRUPTIBLE);
 111                 preempt_disable();
 112                 if (kthread_should_stop()) {
 113                         set_current_state(TASK_RUNNING);
 114                         preempt_enable();
 115                         if (ht->cleanup)
 116                                 ht->cleanup(td->cpu, cpu_online(td->cpu));
 117                         kfree(td);
 118                         return 0;
 119                 }
 120
 121                 if (kthread_should_park()) {
 122                         __set_current_state(TASK_RUNNING);
 123                         preempt_enable();
 124                         if (ht->park && td->status == HP_THREAD_ACTIVE) {
 125                                 BUG_ON(td->cpu != smp_processor_id());
 126                                 ht->park(td->cpu);
 127                                 td->status = HP_THREAD_PARKED;
 128                         }
 129                         kthread_parkme();
 130                         /* We might have been woken for stop */
 131                         continue;
 132                 }
 133
 134                 BUG_ON(td->cpu != smp_processor_id());
 135
 136                 /* Check for state change setup */
 137                 switch (td->status) {
 138                 case HP_THREAD_NONE:
 139                         preempt_enable();
 140                         if (ht->setup)
 141                                 ht->setup(td->cpu);
 142                         td->status = HP_THREAD_ACTIVE;
 143                         preempt_disable();
 144                         break;
 145                 case HP_THREAD_PARKED:
 146                         preempt_enable();
 147                         if (ht->unpark)
 148                                 ht->unpark(td->cpu);
 149                         td->status = HP_THREAD_ACTIVE;
 150                         preempt_disable();
 151                         break;
 152                 }
 153
 154                 if (!ht->thread_should_run(td->cpu)) {
 155                         preempt_enable();
 156                         schedule();
 157                 } else {
 158                         set_current_state(TASK_RUNNING);
 159                         preempt_enable();
 160                         ht->thread_fn(td->cpu);
 161                 }
 162         }
 163 }
 164
 165 static int
 166 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 167 {
 168         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 169         struct smpboot_thread_data *td;
 170
 171         if (tsk)
 172                 return 0;
 173
 174         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
 175         if (!td)
 176                 return -ENOMEM;
 177         td->cpu = cpu;
 178         td->ht = ht;
 179
 180         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
 181                                     ht->thread_comm);
 182         if (IS_ERR(tsk)) {
 183                 kfree(td);
 184                 return PTR_ERR(tsk);
 185         }
 186         get_task_struct(tsk);
 187         *per_cpu_ptr(ht->store, cpu) = tsk;
 188         if (ht->create) {
 189                 /*
 190                  * Make sure that the task has actually scheduled out
 191                  * into park position, before calling the create
 192                  * callback. At least the migration thread callback
 193                  * requires that the task is off the runqueue.
 194                  */
 195                 if (!wait_task_inactive(tsk, TASK_PARKED))
 196                         WARN_ON(1);
 197                 else
 198                         ht->create(cpu);
 199         }
 200         return 0;
 201 }
 202
 203 int smpboot_create_threads(unsigned int cpu)
 204 {
 205         struct smp_hotplug_thread *cur;
 206         int ret = 0;
 207
 208         mutex_lock(&smpboot_threads_lock);
 209         list_for_each_entry(cur, &hotplug_threads, list) {
 210                 ret = __smpboot_create_thread(cur, cpu);
 211                 if (ret)
 212                         break;
 213         }
 214         mutex_unlock(&smpboot_threads_lock);
 215         return ret;
 216 }
 217
 218 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 219 {
 220         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 221
 222         if (ht->pre_unpark)
 223                 ht->pre_unpark(cpu);
 224         kthread_unpark(tsk);
 225 }
 226
 227 void smpboot_unpark_threads(unsigned int cpu)
 228 {
 229         struct smp_hotplug_thread *cur;
 230
 231         mutex_lock(&smpboot_threads_lock);
 232         list_for_each_entry(cur, &hotplug_threads, list)
 233                 smpboot_unpark_thread(cur, cpu);
 234         mutex_unlock(&smpboot_threads_lock);
 235 }
 236
 237 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 238 {
 239         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 240
 241         if (tsk && !ht->selfparking)
 242                 kthread_park(tsk);
 243 }
 244
 245 void smpboot_park_threads(unsigned int cpu)
 246 {
 247         struct smp_hotplug_thread *cur;
 248
 249         mutex_lock(&smpboot_threads_lock);
 250         list_for_each_entry_reverse(cur, &hotplug_threads, list)
 251                 smpboot_park_thread(cur, cpu);
 252         mutex_unlock(&smpboot_threads_lock);
 253 }
 254
 255 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 256 {
 257         unsigned int cpu;
 258
 259         /* We need to destroy also the parked threads of offline cpus */
 260         for_each_possible_cpu(cpu) {
 261                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 262
 263                 if (tsk) {
 264                         kthread_stop(tsk);
 265                         put_task_struct(tsk);
 266                         *per_cpu_ptr(ht->store, cpu) = NULL;
 267                 }
 268         }
 269 }
 270
 271 /**
 272  * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
 273  * @plug_thread:        Hotplug thread descriptor
 274  *
 275  * Creates and starts the threads on all online cpus.
 276  */
 277 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 278 {
 279         unsigned int cpu;
 280         int ret = 0;
 281
 282         mutex_lock(&smpboot_threads_lock);
 283         for_each_online_cpu(cpu) {
 284                 ret = __smpboot_create_thread(plug_thread, cpu);
 285                 if (ret) {
 286                         smpboot_destroy_threads(plug_thread);
 287                         goto out;
 288                 }
 289                 smpboot_unpark_thread(plug_thread, cpu);
 290         }
 291         list_add(&plug_thread->list, &hotplug_threads);
 292 out:
 293         mutex_unlock(&smpboot_threads_lock);
 294         return ret;
 295 }
 296 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
 297
 298 /**
 299  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 300  * @plug_thread:        Hotplug thread descriptor
 301  *
 302  * Stops all threads on all possible cpus.
 303  */
 304 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 305 {
 306         get_online_cpus();
 307         mutex_lock(&smpboot_threads_lock);
 308         list_del(&plug_thread->list);
 309         smpboot_destroy_threads(plug_thread);
 310         mutex_unlock(&smpboot_threads_lock);
 311         put_online_cpus();
 312 }
 313 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);