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                         __set_current_state(TASK_RUNNING);
 140                         preempt_enable();
 141                         if (ht->setup)
 142                                 ht->setup(td->cpu);
 143                         td->status = HP_THREAD_ACTIVE;
 144                         continue;
 145
 146                 case HP_THREAD_PARKED:
 147                         __set_current_state(TASK_RUNNING);
 148                         preempt_enable();
 149                         if (ht->unpark)
 150                                 ht->unpark(td->cpu);
 151                         td->status = HP_THREAD_ACTIVE;
 152                         continue;
 153                 }
 154
 155                 if (!ht->thread_should_run(td->cpu)) {
 156                         preempt_enable_no_resched();
 157                         schedule();
 158                 } else {
 159                         __set_current_state(TASK_RUNNING);
 160                         preempt_enable();
 161                         ht->thread_fn(td->cpu);
 162                 }
 163         }
 164 }
 165
 166 static int
 167 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 168 {
 169         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 170         struct smpboot_thread_data *td;
 171
 172         if (tsk)
 173                 return 0;
 174
 175         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
 176         if (!td)
 177                 return -ENOMEM;
 178         td->cpu = cpu;
 179         td->ht = ht;
 180
 181         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
 182                                     ht->thread_comm);
 183         if (IS_ERR(tsk)) {
 184                 kfree(td);
 185                 return PTR_ERR(tsk);
 186         }
 187         get_task_struct(tsk);
 188         *per_cpu_ptr(ht->store, cpu) = tsk;
 189         if (ht->create) {
 190                 /*
 191                  * Make sure that the task has actually scheduled out
 192                  * into park position, before calling the create
 193                  * callback. At least the migration thread callback
 194                  * requires that the task is off the runqueue.
 195                  */
 196                 if (!wait_task_inactive(tsk, TASK_PARKED))
 197                         WARN_ON(1);
 198                 else
 199                         ht->create(cpu);
 200         }
 201         return 0;
 202 }
 203
 204 int smpboot_create_threads(unsigned int cpu)
 205 {
 206         struct smp_hotplug_thread *cur;
 207         int ret = 0;
 208
 209         mutex_lock(&smpboot_threads_lock);
 210         list_for_each_entry(cur, &hotplug_threads, list) {
 211                 ret = __smpboot_create_thread(cur, cpu);
 212                 if (ret)
 213                         break;
 214         }
 215         mutex_unlock(&smpboot_threads_lock);
 216         return ret;
 217 }
 218
 219 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 220 {
 221         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 222
 223         if (ht->pre_unpark)
 224                 ht->pre_unpark(cpu);
 225         kthread_unpark(tsk);
 226 }
 227
 228 void smpboot_unpark_threads(unsigned int cpu)
 229 {
 230         struct smp_hotplug_thread *cur;
 231
 232         mutex_lock(&smpboot_threads_lock);
 233         list_for_each_entry(cur, &hotplug_threads, list)
 234                 smpboot_unpark_thread(cur, cpu);
 235         mutex_unlock(&smpboot_threads_lock);
 236 }
 237
 238 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 239 {
 240         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 241
 242         if (tsk && !ht->selfparking)
 243                 kthread_park(tsk);
 244 }
 245
 246 void smpboot_park_threads(unsigned int cpu)
 247 {
 248         struct smp_hotplug_thread *cur;
 249
 250         mutex_lock(&smpboot_threads_lock);
 251         list_for_each_entry_reverse(cur, &hotplug_threads, list)
 252                 smpboot_park_thread(cur, cpu);
 253         mutex_unlock(&smpboot_threads_lock);
 254 }
 255
 256 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 257 {
 258         unsigned int cpu;
 259
 260         /* We need to destroy also the parked threads of offline cpus */
 261         for_each_possible_cpu(cpu) {
 262                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 263
 264                 if (tsk) {
 265                         kthread_stop(tsk);
 266                         put_task_struct(tsk);
 267                         *per_cpu_ptr(ht->store, cpu) = NULL;
 268                 }
 269         }
 270 }
 271
 272 /**
 273  * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
 274  * @plug_thread:        Hotplug thread descriptor
 275  *
 276  * Creates and starts the threads on all online cpus.
 277  */
 278 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 279 {
 280         unsigned int cpu;
 281         int ret = 0;
 282
 283         mutex_lock(&smpboot_threads_lock);
 284         for_each_online_cpu(cpu) {
 285                 ret = __smpboot_create_thread(plug_thread, cpu);
 286                 if (ret) {
 287                         smpboot_destroy_threads(plug_thread);
 288                         goto out;
 289                 }
 290                 smpboot_unpark_thread(plug_thread, cpu);
 291         }
 292         list_add(&plug_thread->list, &hotplug_threads);
 293 out:
 294         mutex_unlock(&smpboot_threads_lock);
 295         return ret;
 296 }
 297 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
 298
 299 /**
 300  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 301  * @plug_thread:        Hotplug thread descriptor
 302  *
 303  * Stops all threads on all possible cpus.
 304  */
 305 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 306 {
 307         get_online_cpus();
 308         mutex_lock(&smpboot_threads_lock);
 309         list_del(&plug_thread->list);
 310         smpboot_destroy_threads(plug_thread);
 311         mutex_unlock(&smpboot_threads_lock);
 312         put_online_cpus();
 313 }
 314 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);