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/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/export.h>
  13 #include <linux/percpu.h>
  14 #include <linux/kthread.h>
  15 #include <linux/smpboot.h>
  16
  17 #include "smpboot.h"
  18
  19 #ifdef CONFIG_SMP
  20
  21 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
  22 /*
  23  * For the hotplug case we keep the task structs around and reuse
  24  * them.
  25  */
  26 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
  27
  28 struct task_struct *idle_thread_get(unsigned int cpu)
  29 {
  30         struct task_struct *tsk = per_cpu(idle_threads, cpu);
  31
  32         if (!tsk)
  33                 return ERR_PTR(-ENOMEM);
  34         init_idle(tsk, cpu);
  35         return tsk;
  36 }
  37
  38 void __init idle_thread_set_boot_cpu(void)
  39 {
  40         per_cpu(idle_threads, smp_processor_id()) = current;
  41 }
  42
  43 /**
  44  * idle_init - Initialize the idle thread for a cpu
  45  * @cpu:        The cpu for which the idle thread should be initialized
  46  *
  47  * Creates the thread if it does not exist.
  48  */
  49 static inline void idle_init(unsigned int cpu)
  50 {
  51         struct task_struct *tsk = per_cpu(idle_threads, cpu);
  52
  53         if (!tsk) {
  54                 tsk = fork_idle(cpu);
  55                 if (IS_ERR(tsk))
  56                         pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
  57                 else
  58                         per_cpu(idle_threads, cpu) = tsk;
  59         }
  60 }
  61
  62 /**
  63  * idle_threads_init - Initialize idle threads for all cpus
  64  */
  65 void __init idle_threads_init(void)
  66 {
  67         unsigned int cpu, boot_cpu;
  68
  69         boot_cpu = smp_processor_id();
  70
  71         for_each_possible_cpu(cpu) {
  72                 if (cpu != boot_cpu)
  73                         idle_init(cpu);
  74         }
  75 }
  76 #endif
  77
  78 #endif /* #ifdef CONFIG_SMP */
  79
  80 static LIST_HEAD(hotplug_threads);
  81 static DEFINE_MUTEX(smpboot_threads_lock);
  82
  83 struct smpboot_thread_data {
  84         unsigned int                    cpu;
  85         unsigned int                    status;
  86         struct smp_hotplug_thread       *ht;
  87 };
  88
  89 enum {
  90         HP_THREAD_NONE = 0,
  91         HP_THREAD_ACTIVE,
  92         HP_THREAD_PARKED,
  93 };
  94
  95 /**
  96  * smpboot_thread_fn - percpu hotplug thread loop function
  97  * @data:       thread data pointer
  98  *
  99  * Checks for thread stop and park conditions. Calls the necessary
 100  * setup, cleanup, park and unpark functions for the registered
 101  * thread.
 102  *
 103  * Returns 1 when the thread should exit, 0 otherwise.
 104  */
 105 static int smpboot_thread_fn(void *data)
 106 {
 107         struct smpboot_thread_data *td = data;
 108         struct smp_hotplug_thread *ht = td->ht;
 109
 110         while (1) {
 111                 set_current_state(TASK_INTERRUPTIBLE);
 112                 preempt_disable();
 113                 if (kthread_should_stop()) {
 114                         __set_current_state(TASK_RUNNING);
 115                         preempt_enable();
 116                         if (ht->cleanup)
 117                                 ht->cleanup(td->cpu, cpu_online(td->cpu));
 118                         kfree(td);
 119                         return 0;
 120                 }
 121
 122                 if (kthread_should_park()) {
 123                         __set_current_state(TASK_RUNNING);
 124                         preempt_enable();
 125                         if (ht->park && td->status == HP_THREAD_ACTIVE) {
 126                                 BUG_ON(td->cpu != smp_processor_id());
 127                                 ht->park(td->cpu);
 128                                 td->status = HP_THREAD_PARKED;
 129                         }
 130                         kthread_parkme();
 131                         /* We might have been woken for stop */
 132                         continue;
 133                 }
 134
 135                 BUG_ON(td->cpu != smp_processor_id());
 136
 137                 /* Check for state change setup */
 138                 switch (td->status) {
 139                 case HP_THREAD_NONE:
 140                         __set_current_state(TASK_RUNNING);
 141                         preempt_enable();
 142                         if (ht->setup)
 143                                 ht->setup(td->cpu);
 144                         td->status = HP_THREAD_ACTIVE;
 145                         continue;
 146
 147                 case HP_THREAD_PARKED:
 148                         __set_current_state(TASK_RUNNING);
 149                         preempt_enable();
 150                         if (ht->unpark)
 151                                 ht->unpark(td->cpu);
 152                         td->status = HP_THREAD_ACTIVE;
 153                         continue;
 154                 }
 155
 156                 if (!ht->thread_should_run(td->cpu)) {
 157                         preempt_enable_no_resched();
 158                         schedule();
 159                 } else {
 160                         __set_current_state(TASK_RUNNING);
 161                         preempt_enable();
 162                         ht->thread_fn(td->cpu);
 163                 }
 164         }
 165 }
 166
 167 static int
 168 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 169 {
 170         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 171         struct smpboot_thread_data *td;
 172
 173         if (tsk)
 174                 return 0;
 175
 176         td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
 177         if (!td)
 178                 return -ENOMEM;
 179         td->cpu = cpu;
 180         td->ht = ht;
 181
 182         tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
 183                                     ht->thread_comm);
 184         if (IS_ERR(tsk)) {
 185                 kfree(td);
 186                 return PTR_ERR(tsk);
 187         }
 188         get_task_struct(tsk);
 189         *per_cpu_ptr(ht->store, cpu) = tsk;
 190         if (ht->create) {
 191                 /*
 192                  * Make sure that the task has actually scheduled out
 193                  * into park position, before calling the create
 194                  * callback. At least the migration thread callback
 195                  * requires that the task is off the runqueue.
 196                  */
 197                 if (!wait_task_inactive(tsk, TASK_PARKED))
 198                         WARN_ON(1);
 199                 else
 200                         ht->create(cpu);
 201         }
 202         return 0;
 203 }
 204
 205 int smpboot_create_threads(unsigned int cpu)
 206 {
 207         struct smp_hotplug_thread *cur;
 208         int ret = 0;
 209
 210         mutex_lock(&smpboot_threads_lock);
 211         list_for_each_entry(cur, &hotplug_threads, list) {
 212                 ret = __smpboot_create_thread(cur, cpu);
 213                 if (ret)
 214                         break;
 215         }
 216         mutex_unlock(&smpboot_threads_lock);
 217         return ret;
 218 }
 219
 220 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 221 {
 222         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 223
 224         if (ht->pre_unpark)
 225                 ht->pre_unpark(cpu);
 226         kthread_unpark(tsk);
 227 }
 228
 229 void smpboot_unpark_threads(unsigned int cpu)
 230 {
 231         struct smp_hotplug_thread *cur;
 232
 233         mutex_lock(&smpboot_threads_lock);
 234         list_for_each_entry(cur, &hotplug_threads, list)
 235                 smpboot_unpark_thread(cur, cpu);
 236         mutex_unlock(&smpboot_threads_lock);
 237 }
 238
 239 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
 240 {
 241         struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 242
 243         if (tsk && !ht->selfparking)
 244                 kthread_park(tsk);
 245 }
 246
 247 void smpboot_park_threads(unsigned int cpu)
 248 {
 249         struct smp_hotplug_thread *cur;
 250
 251         mutex_lock(&smpboot_threads_lock);
 252         list_for_each_entry_reverse(cur, &hotplug_threads, list)
 253                 smpboot_park_thread(cur, cpu);
 254         mutex_unlock(&smpboot_threads_lock);
 255 }
 256
 257 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
 258 {
 259         unsigned int cpu;
 260
 261         /* We need to destroy also the parked threads of offline cpus */
 262         for_each_possible_cpu(cpu) {
 263                 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
 264
 265                 if (tsk) {
 266                         kthread_stop(tsk);
 267                         put_task_struct(tsk);
 268                         *per_cpu_ptr(ht->store, cpu) = NULL;
 269                 }
 270         }
 271 }
 272
 273 /**
 274  * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug
 275  * @plug_thread:        Hotplug thread descriptor
 276  *
 277  * Creates and starts the threads on all online cpus.
 278  */
 279 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 280 {
 281         unsigned int cpu;
 282         int ret = 0;
 283
 284         get_online_cpus();
 285         mutex_lock(&smpboot_threads_lock);
 286         for_each_online_cpu(cpu) {
 287                 ret = __smpboot_create_thread(plug_thread, cpu);
 288                 if (ret) {
 289                         smpboot_destroy_threads(plug_thread);
 290                         goto out;
 291                 }
 292                 smpboot_unpark_thread(plug_thread, cpu);
 293         }
 294         list_add(&plug_thread->list, &hotplug_threads);
 295 out:
 296         mutex_unlock(&smpboot_threads_lock);
 297         put_online_cpus();
 298         return ret;
 299 }
 300 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
 301
 302 /**
 303  * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 304  * @plug_thread:        Hotplug thread descriptor
 305  *
 306  * Stops all threads on all possible cpus.
 307  */
 308 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 309 {
 310         get_online_cpus();
 311         mutex_lock(&smpboot_threads_lock);
 312         list_del(&plug_thread->list);
 313         smpboot_destroy_threads(plug_thread);
 314         mutex_unlock(&smpboot_threads_lock);
 315         put_online_cpus();
 316 }
 317 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
 318
 319 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
 320
 321 /*
 322  * Called to poll specified CPU's state, for example, when waiting for
 323  * a CPU to come online.
 324  */
 325 int cpu_report_state(int cpu)
 326 {
 327         return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
 328 }
 329
 330 /*
 331  * If CPU has died properly, set its state to CPU_UP_PREPARE and
 332  * return success.  Otherwise, return -EBUSY if the CPU died after
 333  * cpu_wait_death() timed out.  And yet otherwise again, return -EAGAIN
 334  * if cpu_wait_death() timed out and the CPU still hasn't gotten around
 335  * to dying.  In the latter two cases, the CPU might not be set up
 336  * properly, but it is up to the arch-specific code to decide.
 337  * Finally, -EIO indicates an unanticipated problem.
 338  *
 339  * Note that it is permissible to omit this call entirely, as is
 340  * done in architectures that do no CPU-hotplug error checking.
 341  */
 342 int cpu_check_up_prepare(int cpu)
 343 {
 344         if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
 345                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
 346                 return 0;
 347         }
 348
 349         switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
 350
 351         case CPU_POST_DEAD:
 352
 353                 /* The CPU died properly, so just start it up again. */
 354                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
 355                 return 0;
 356
 357         case CPU_DEAD_FROZEN:
 358
 359                 /*
 360                  * Timeout during CPU death, so let caller know.
 361                  * The outgoing CPU completed its processing, but after
 362                  * cpu_wait_death() timed out and reported the error. The
 363                  * caller is free to proceed, in which case the state
 364                  * will be reset properly by cpu_set_state_online().
 365                  * Proceeding despite this -EBUSY return makes sense
 366                  * for systems where the outgoing CPUs take themselves
 367                  * offline, with no post-death manipulation required from
 368                  * a surviving CPU.
 369                  */
 370                 return -EBUSY;
 371
 372         case CPU_BROKEN:
 373
 374                 /*
 375                  * The most likely reason we got here is that there was
 376                  * a timeout during CPU death, and the outgoing CPU never
 377                  * did complete its processing.  This could happen on
 378                  * a virtualized system if the outgoing VCPU gets preempted
 379                  * for more than five seconds, and the user attempts to
 380                  * immediately online that same CPU.  Trying again later
 381                  * might return -EBUSY above, hence -EAGAIN.
 382                  */
 383                 return -EAGAIN;
 384
 385         default:
 386
 387                 /* Should not happen.  Famous last words. */
 388                 return -EIO;
 389         }
 390 }
 391
 392 /*
 393  * Mark the specified CPU online.
 394  *
 395  * Note that it is permissible to omit this call entirely, as is
 396  * done in architectures that do no CPU-hotplug error checking.
 397  */
 398 void cpu_set_state_online(int cpu)
 399 {
 400         (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
 401 }
 402
 403 #ifdef CONFIG_HOTPLUG_CPU
 404
 405 /*
 406  * Wait for the specified CPU to exit the idle loop and die.
 407  */
 408 bool cpu_wait_death(unsigned int cpu, int seconds)
 409 {
 410         int jf_left = seconds * HZ;
 411         int oldstate;
 412         bool ret = true;
 413         int sleep_jf = 1;
 414
 415         might_sleep();
 416
 417         /* The outgoing CPU will normally get done quite quickly. */
 418         if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
 419                 goto update_state;
 420         udelay(5);
 421
 422         /* But if the outgoing CPU dawdles, wait increasingly long times. */
 423         while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
 424                 schedule_timeout_uninterruptible(sleep_jf);
 425                 jf_left -= sleep_jf;
 426                 if (jf_left <= 0)
 427                         break;
 428                 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
 429         }
 430 update_state:
 431         oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
 432         if (oldstate == CPU_DEAD) {
 433                 /* Outgoing CPU died normally, update state. */
 434                 smp_mb(); /* atomic_read() before update. */
 435                 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
 436         } else {
 437                 /* Outgoing CPU still hasn't died, set state accordingly. */
 438                 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
 439                                    oldstate, CPU_BROKEN) != oldstate)
 440                         goto update_state;
 441                 ret = false;
 442         }
 443         return ret;
 444 }
 445
 446 /*
 447  * Called by the outgoing CPU to report its successful death.  Return
 448  * false if this report follows the surviving CPU's timing out.
 449  *
 450  * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
 451  * timed out.  This approach allows architectures to omit calls to
 452  * cpu_check_up_prepare() and cpu_set_state_online() without defeating
 453  * the next cpu_wait_death()'s polling loop.
 454  */
 455 bool cpu_report_death(void)
 456 {
 457         int oldstate;
 458         int newstate;
 459         int cpu = smp_processor_id();
 460
 461         do {
 462                 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
 463                 if (oldstate != CPU_BROKEN)
 464                         newstate = CPU_DEAD;
 465                 else
 466                         newstate = CPU_DEAD_FROZEN;
 467         } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
 468                                 oldstate, newstate) != oldstate);
 469         return newstate == CPU_DEAD;
 470 }
 471
 472 #endif /* #ifdef CONFIG_HOTPLUG_CPU */