kernel/cpu.c

   1 /* CPU control.
   2  * (C) 2001, 2002, 2003, 2004 Rusty Russell
   3  *
   4  * This code is licenced under the GPL.
   5  */
   6 #include <linux/proc_fs.h>
   7 #include <linux/smp.h>
   8 #include <linux/init.h>
   9 #include <linux/notifier.h>
  10 #include <linux/sched.h>
  11 #include <linux/unistd.h>
  12 #include <linux/cpu.h>
  13 #include <linux/module.h>
  14 #include <linux/kthread.h>
  15 #include <linux/stop_machine.h>
  16 #include <linux/mutex.h>
  17 #include <linux/gfp.h>
  18
  19 #ifdef CONFIG_SMP
  20 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
  21 static DEFINE_MUTEX(cpu_add_remove_lock);
  22
  23 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  24
  25 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  26  * Should always be manipulated under cpu_add_remove_lock
  27  */
  28 static int cpu_hotplug_disabled;
  29
  30 static struct {
  31         struct task_struct *active_writer;
  32         struct mutex lock; /* Synchronizes accesses to refcount, */
  33         /*
  34          * Also blocks the new readers during
  35          * an ongoing cpu hotplug operation.
  36          */
  37         int refcount;
  38 } cpu_hotplug = {
  39         .active_writer = NULL,
  40         .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
  41         .refcount = 0,
  42 };
  43
  44 #ifdef CONFIG_HOTPLUG_CPU
  45
  46 void get_online_cpus(void)
  47 {
  48         might_sleep();
  49         if (cpu_hotplug.active_writer == current)
  50                 return;
  51         mutex_lock(&cpu_hotplug.lock);
  52         cpu_hotplug.refcount++;
  53         mutex_unlock(&cpu_hotplug.lock);
  54
  55 }
  56 EXPORT_SYMBOL_GPL(get_online_cpus);
  57
  58 void put_online_cpus(void)
  59 {
  60         if (cpu_hotplug.active_writer == current)
  61                 return;
  62         mutex_lock(&cpu_hotplug.lock);
  63         if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  64                 wake_up_process(cpu_hotplug.active_writer);
  65         mutex_unlock(&cpu_hotplug.lock);
  66
  67 }
  68 EXPORT_SYMBOL_GPL(put_online_cpus);
  69
  70 #endif  /* CONFIG_HOTPLUG_CPU */
  71
  72 /*
  73  * The following two API's must be used when attempting
  74  * to serialize the updates to cpu_online_mask, cpu_present_mask.
  75  */
  76 void cpu_maps_update_begin(void)
  77 {
  78         mutex_lock(&cpu_add_remove_lock);
  79 }
  80
  81 void cpu_maps_update_done(void)
  82 {
  83         mutex_unlock(&cpu_add_remove_lock);
  84 }
  85
  86 /*
  87  * This ensures that the hotplug operation can begin only when the
  88  * refcount goes to zero.
  89  *
  90  * Note that during a cpu-hotplug operation, the new readers, if any,
  91  * will be blocked by the cpu_hotplug.lock
  92  *
  93  * Since cpu_hotplug_begin() is always called after invoking
  94  * cpu_maps_update_begin(), we can be sure that only one writer is active.
  95  *
  96  * Note that theoretically, there is a possibility of a livelock:
  97  * - Refcount goes to zero, last reader wakes up the sleeping
  98  *   writer.
  99  * - Last reader unlocks the cpu_hotplug.lock.
 100  * - A new reader arrives at this moment, bumps up the refcount.
 101  * - The writer acquires the cpu_hotplug.lock finds the refcount
 102  *   non zero and goes to sleep again.
 103  *
 104  * However, this is very difficult to achieve in practice since
 105  * get_online_cpus() not an api which is called all that often.
 106  *
 107  */
 108 static void cpu_hotplug_begin(void)
 109 {
 110         cpu_hotplug.active_writer = current;
 111
 112         for (;;) {
 113                 mutex_lock(&cpu_hotplug.lock);
 114                 if (likely(!cpu_hotplug.refcount))
 115                         break;
 116                 __set_current_state(TASK_UNINTERRUPTIBLE);
 117                 mutex_unlock(&cpu_hotplug.lock);
 118                 schedule();
 119         }
 120 }
 121
 122 static void cpu_hotplug_done(void)
 123 {
 124         cpu_hotplug.active_writer = NULL;
 125         mutex_unlock(&cpu_hotplug.lock);
 126 }
 127 /* Need to know about CPUs going up/down? */
 128 int __ref register_cpu_notifier(struct notifier_block *nb)
 129 {
 130         int ret;
 131         cpu_maps_update_begin();
 132         ret = raw_notifier_chain_register(&cpu_chain, nb);
 133         cpu_maps_update_done();
 134         return ret;
 135 }
 136
 137 #ifdef CONFIG_HOTPLUG_CPU
 138
 139 EXPORT_SYMBOL(register_cpu_notifier);
 140
 141 void __ref unregister_cpu_notifier(struct notifier_block *nb)
 142 {
 143         cpu_maps_update_begin();
 144         raw_notifier_chain_unregister(&cpu_chain, nb);
 145         cpu_maps_update_done();
 146 }
 147 EXPORT_SYMBOL(unregister_cpu_notifier);
 148
 149 static inline void check_for_tasks(int cpu)
 150 {
 151         struct task_struct *p;
 152
 153         write_lock_irq(&tasklist_lock);
 154         for_each_process(p) {
 155                 if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
 156                     (!cputime_eq(p->utime, cputime_zero) ||
 157                      !cputime_eq(p->stime, cputime_zero)))
 158                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
 159                                 "(state = %ld, flags = %x)\n",
 160                                 p->comm, task_pid_nr(p), cpu,
 161                                 p->state, p->flags);
 162         }
 163         write_unlock_irq(&tasklist_lock);
 164 }
 165
 166 struct take_cpu_down_param {
 167         struct task_struct *caller;
 168         unsigned long mod;
 169         void *hcpu;
 170 };
 171
 172 /* Take this CPU down. */
 173 static int __ref take_cpu_down(void *_param)
 174 {
 175         struct take_cpu_down_param *param = _param;
 176         unsigned int cpu = (unsigned long)param->hcpu;
 177         int err;
 178
 179         /* Ensure this CPU doesn't handle any more interrupts. */
 180         err = __cpu_disable();
 181         if (err < 0)
 182                 return err;
 183
 184         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 185                                 param->hcpu);
 186
 187         if (task_cpu(param->caller) == cpu)
 188                 move_task_off_dead_cpu(cpu, param->caller);
 189         /* Force idle task to run as soon as we yield: it should
 190            immediately notice cpu is offline and die quickly. */
 191         sched_idle_next();
 192         return 0;
 193 }
 194
 195 /* Requires cpu_add_remove_lock to be held */
 196 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 197 {
 198         int err, nr_calls = 0;
 199         void *hcpu = (void *)(long)cpu;
 200         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 201         struct take_cpu_down_param tcd_param = {
 202                 .caller = current,
 203                 .mod = mod,
 204                 .hcpu = hcpu,
 205         };
 206
 207         if (num_online_cpus() == 1)
 208                 return -EBUSY;
 209
 210         if (!cpu_online(cpu))
 211                 return -EINVAL;
 212
 213         cpu_hotplug_begin();
 214         set_cpu_active(cpu, false);
 215         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 216                                         hcpu, -1, &nr_calls);
 217         if (err == NOTIFY_BAD) {
 218                 set_cpu_active(cpu, true);
 219
 220                 nr_calls--;
 221                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 222                                           hcpu, nr_calls, NULL);
 223                 printk("%s: attempt to take down CPU %u failed\n",
 224                                 __func__, cpu);
 225                 err = -EINVAL;
 226                 goto out_release;
 227         }
 228
 229         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
 230         if (err) {
 231                 set_cpu_active(cpu, true);
 232                 /* CPU didn't die: tell everyone.  Can't complain. */
 233                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 234                                             hcpu) == NOTIFY_BAD)
 235                         BUG();
 236
 237                 goto out_release;
 238         }
 239         BUG_ON(cpu_online(cpu));
 240
 241         /* Wait for it to sleep (leaving idle task). */
 242         while (!idle_cpu(cpu))
 243                 yield();
 244
 245         /* This actually kills the CPU. */
 246         __cpu_die(cpu);
 247
 248         /* CPU is completely dead: tell everyone.  Too late to complain. */
 249         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 250                                     hcpu) == NOTIFY_BAD)
 251                 BUG();
 252
 253         check_for_tasks(cpu);
 254
 255 out_release:
 256         cpu_hotplug_done();
 257         if (!err) {
 258                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 259                                             hcpu) == NOTIFY_BAD)
 260                         BUG();
 261         }
 262         return err;
 263 }
 264
 265 int __ref cpu_down(unsigned int cpu)
 266 {
 267         int err;
 268
 269         cpu_maps_update_begin();
 270
 271         if (cpu_hotplug_disabled) {
 272                 err = -EBUSY;
 273                 goto out;
 274         }
 275
 276         err = _cpu_down(cpu, 0);
 277
 278 out:
 279         cpu_maps_update_done();
 280         return err;
 281 }
 282 EXPORT_SYMBOL(cpu_down);
 283 #endif /*CONFIG_HOTPLUG_CPU*/
 284
 285 /* Requires cpu_add_remove_lock to be held */
 286 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 287 {
 288         int ret, nr_calls = 0;
 289         void *hcpu = (void *)(long)cpu;
 290         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 291
 292         if (cpu_online(cpu) || !cpu_present(cpu))
 293                 return -EINVAL;
 294
 295         cpu_hotplug_begin();
 296         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 297                                                         -1, &nr_calls);
 298         if (ret == NOTIFY_BAD) {
 299                 nr_calls--;
 300                 printk("%s: attempt to bring up CPU %u failed\n",
 301                                 __func__, cpu);
 302                 ret = -EINVAL;
 303                 goto out_notify;
 304         }
 305
 306         /* Arch-specific enabling code. */
 307         ret = __cpu_up(cpu);
 308         if (ret != 0)
 309                 goto out_notify;
 310         BUG_ON(!cpu_online(cpu));
 311
 312         set_cpu_active(cpu, true);
 313
 314         /* Now call notifier in preparation. */
 315         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 316
 317 out_notify:
 318         if (ret != 0)
 319                 __raw_notifier_call_chain(&cpu_chain,
 320                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 321         cpu_hotplug_done();
 322
 323         return ret;
 324 }
 325
 326 int __cpuinit cpu_up(unsigned int cpu)
 327 {
 328         int err = 0;
 329         if (!cpu_possible(cpu)) {
 330                 printk(KERN_ERR "can't online cpu %d because it is not "
 331                         "configured as may-hotadd at boot time\n", cpu);
 332 #if defined(CONFIG_IA64)
 333                 printk(KERN_ERR "please check additional_cpus= boot "
 334                                 "parameter\n");
 335 #endif
 336                 return -EINVAL;
 337         }
 338
 339         cpu_maps_update_begin();
 340
 341         if (cpu_hotplug_disabled) {
 342                 err = -EBUSY;
 343                 goto out;
 344         }
 345
 346         err = _cpu_up(cpu, 0);
 347
 348 out:
 349         cpu_maps_update_done();
 350         return err;
 351 }
 352
 353 #ifdef CONFIG_PM_SLEEP_SMP
 354 static cpumask_var_t frozen_cpus;
 355
 356 int disable_nonboot_cpus(void)
 357 {
 358         int cpu, first_cpu, error;
 359
 360         cpu_maps_update_begin();
 361         first_cpu = cpumask_first(cpu_online_mask);
 362         /*
 363          * We take down all of the non-boot CPUs in one shot to avoid races
 364          * with the userspace trying to use the CPU hotplug at the same time
 365          */
 366         cpumask_clear(frozen_cpus);
 367
 368         printk("Disabling non-boot CPUs ...\n");
 369         for_each_online_cpu(cpu) {
 370                 if (cpu == first_cpu)
 371                         continue;
 372                 error = _cpu_down(cpu, 1);
 373                 if (!error)
 374                         cpumask_set_cpu(cpu, frozen_cpus);
 375                 else {
 376                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 377                                 cpu, error);
 378                         break;
 379                 }
 380         }
 381
 382         if (!error) {
 383                 BUG_ON(num_online_cpus() > 1);
 384                 /* Make sure the CPUs won't be enabled by someone else */
 385                 cpu_hotplug_disabled = 1;
 386         } else {
 387                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 388         }
 389         cpu_maps_update_done();
 390         return error;
 391 }
 392
 393 void __weak arch_enable_nonboot_cpus_begin(void)
 394 {
 395 }
 396
 397 void __weak arch_enable_nonboot_cpus_end(void)
 398 {
 399 }
 400
 401 void __ref enable_nonboot_cpus(void)
 402 {
 403         int cpu, error;
 404
 405         /* Allow everyone to use the CPU hotplug again */
 406         cpu_maps_update_begin();
 407         cpu_hotplug_disabled = 0;
 408         if (cpumask_empty(frozen_cpus))
 409                 goto out;
 410
 411         printk("Enabling non-boot CPUs ...\n");
 412
 413         arch_enable_nonboot_cpus_begin();
 414
 415         for_each_cpu(cpu, frozen_cpus) {
 416                 error = _cpu_up(cpu, 1);
 417                 if (!error) {
 418                         printk("CPU%d is up\n", cpu);
 419                         continue;
 420                 }
 421                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 422         }
 423
 424         arch_enable_nonboot_cpus_end();
 425
 426         cpumask_clear(frozen_cpus);
 427 out:
 428         cpu_maps_update_done();
 429 }
 430
 431 static int alloc_frozen_cpus(void)
 432 {
 433         if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
 434                 return -ENOMEM;
 435         return 0;
 436 }
 437 core_initcall(alloc_frozen_cpus);
 438 #endif /* CONFIG_PM_SLEEP_SMP */
 439
 440 /**
 441  * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
 442  * @cpu: cpu that just started
 443  *
 444  * This function calls the cpu_chain notifiers with CPU_STARTING.
 445  * It must be called by the arch code on the new cpu, before the new cpu
 446  * enables interrupts and before the "boot" cpu returns from __cpu_up().
 447  */
 448 void __cpuinit notify_cpu_starting(unsigned int cpu)
 449 {
 450         unsigned long val = CPU_STARTING;
 451
 452 #ifdef CONFIG_PM_SLEEP_SMP
 453         if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
 454                 val = CPU_STARTING_FROZEN;
 455 #endif /* CONFIG_PM_SLEEP_SMP */
 456         raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
 457 }
 458
 459 #endif /* CONFIG_SMP */
 460
 461 /*
 462  * cpu_bit_bitmap[] is a special, "compressed" data structure that
 463  * represents all NR_CPUS bits binary values of 1<<nr.
 464  *
 465  * It is used by cpumask_of() to get a constant address to a CPU
 466  * mask value that has a single bit set only.
 467  */
 468
 469 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 470 #define MASK_DECLARE_1(x)       [x+1][0] = 1UL << (x)
 471 #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 472 #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 473 #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 474
 475 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 476
 477         MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
 478         MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 479 #if BITS_PER_LONG > 32
 480         MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
 481         MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 482 #endif
 483 };
 484 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 485
 486 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 487 EXPORT_SYMBOL(cpu_all_bits);
 488
 489 #ifdef CONFIG_INIT_ALL_POSSIBLE
 490 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
 491         = CPU_BITS_ALL;
 492 #else
 493 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
 494 #endif
 495 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
 496 EXPORT_SYMBOL(cpu_possible_mask);
 497
 498 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
 499 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
 500 EXPORT_SYMBOL(cpu_online_mask);
 501
 502 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
 503 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
 504 EXPORT_SYMBOL(cpu_present_mask);
 505
 506 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
 507 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
 508 EXPORT_SYMBOL(cpu_active_mask);
 509
 510 void set_cpu_possible(unsigned int cpu, bool possible)
 511 {
 512         if (possible)
 513                 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
 514         else
 515                 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
 516 }
 517
 518 void set_cpu_present(unsigned int cpu, bool present)
 519 {
 520         if (present)
 521                 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
 522         else
 523                 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
 524 }
 525
 526 void set_cpu_online(unsigned int cpu, bool online)
 527 {
 528         if (online)
 529                 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
 530         else
 531                 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
 532 }
 533
 534 void set_cpu_active(unsigned int cpu, bool active)
 535 {
 536         if (active)
 537                 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
 538         else
 539                 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
 540 }
 541
 542 void init_cpu_present(const struct cpumask *src)
 543 {
 544         cpumask_copy(to_cpumask(cpu_present_bits), src);
 545 }
 546
 547 void init_cpu_possible(const struct cpumask *src)
 548 {
 549         cpumask_copy(to_cpumask(cpu_possible_bits), src);
 550 }
 551
 552 void init_cpu_online(const struct cpumask *src)
 553 {
 554         cpumask_copy(to_cpumask(cpu_online_bits), src);
 555 }