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 * __cpuinit 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
 187         get_task_struct(tsk);
 188         *per_cpu_ptr(ht->store, cpu) = tsk;
 189         return 0;
 190 }
 191
 192 int smpboot_create_threads(unsigned int cpu)
 193 {
 194         struct smp_hotplug_thread *cur;
 195         int ret = 0;
 196
 197         mutex_lock(&smpboot_threads_lock);
 198         list_for_each_entry(cur, &hotplug_threads, list) {
 199                 ret = __smpboot_create_thread(cur, cpu);
 200                 if (ret)
 201                         break;
 202         }
 203         mutex_unlock(&smpboot_threads_lock);
 204         return ret;
 205 }
 206
 207 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 208 {
 209         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 210
 211         kthread_unpark(tsk);
 212 }
 213
 214 void smpboot_unpark_threads(unsigned int cpu)
 215 {
 216         struct smp_hotplug_thread *cur;
 217
 218         mutex_lock(&smpboot_threads_lock);
 219         list_for_each_entry(cur, &hotplug_threads, list)
 220                 smpboot_unpark_thread(cur, cpu);
 221         mutex_unlock(&smpboot_threads_lock);
 222 }
 223
 224 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 225 {
 226         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 227
 228         if (tsk)
 229                 kthread_park(tsk);
 230 }
 231
 232 void smpboot_park_threads(unsigned int cpu)
 233 {
 234         struct smp_hotplug_thread *cur;
 235
 236         mutex_lock(&smpboot_threads_lock);
 237         list_for_each_entry_reverse(cur, &hotplug_threads, list)
 238                 smpboot_park_thread(cur, cpu);
 239         mutex_unlock(&smpboot_threads_lock);
 240 }
 241
 242 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 243 {
 244         unsigned int cpu;
 245
 246         /* We need to destroy also the parked threads of offline cpus */
 247         for_each_possible_cpu(cpu) {
 248                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 249
 250                 if (tsk) {
 251                         kthread_stop(tsk);
 252                         put_task_struct(tsk);
 253                         *per_cpu_ptr(ht->store, cpu) = NULL;
 254                 }
 255         }
 256 }
 257
 258 /**
 259  * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
 260  * @plug_thread:        Hotplug thread descriptor
 261  *
 262  * Creates and starts the threads on all online cpus.
 263  */
 264 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 265 {
 266         unsigned int cpu;
 267         int ret = 0;
 268
 269         mutex_lock(&smpboot_threads_lock);
 270         for_each_online_cpu(cpu) {
 271                 ret = __smpboot_create_thread(plug_thread, cpu);
 272                 if (ret) {
 273                         smpboot_destroy_threads(plug_thread);
 274                         goto out;
 275                 }
 276                 smpboot_unpark_thread(plug_thread, cpu);
 277         }
 278         list_add(&plug_thread->list, &hotplug_threads);
 279 out:
 280         mutex_unlock(&smpboot_threads_lock);
 281         return ret;
 282 }
 283 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
 284
 285 /**
 286  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 287  * @plug_thread:        Hotplug thread descriptor
 288  *
 289  * Stops all threads on all possible cpus.
 290  */
 291 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 292 {
 293         get_online_cpus();
 294         mutex_lock(&smpboot_threads_lock);
 295         list_del(&plug_thread->list);
 296         smpboot_destroy_threads(plug_thread);
 297         mutex_unlock(&smpboot_threads_lock);
 298         put_online_cpus();
 299 }
 300 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);