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
  18 #ifdef CONFIG_SMP
  19 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
  20 static DEFINE_MUTEX(cpu_add_remove_lock);
  21
  22 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  23
  24 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  25  * Should always be manipulated under cpu_add_remove_lock
  26  */
  27 static int cpu_hotplug_disabled;
  28
  29 static struct {
  30         struct task_struct *active_writer;
  31         struct mutex lock; /* Synchronizes accesses to refcount, */
  32         /*
  33          * Also blocks the new readers during
  34          * an ongoing cpu hotplug operation.
  35          */
  36         int refcount;
  37 } cpu_hotplug;
  38
  39 void __init cpu_hotplug_init(void)
  40 {
  41         cpu_hotplug.active_writer = NULL;
  42         mutex_init(&cpu_hotplug.lock);
  43         cpu_hotplug.refcount = 0;
  44 }
  45
  46 #ifdef CONFIG_HOTPLUG_CPU
  47
  48 void get_online_cpus(void)
  49 {
  50         might_sleep();
  51         if (cpu_hotplug.active_writer == current)
  52                 return;
  53         mutex_lock(&cpu_hotplug.lock);
  54         cpu_hotplug.refcount++;
  55         mutex_unlock(&cpu_hotplug.lock);
  56
  57 }
  58 EXPORT_SYMBOL_GPL(get_online_cpus);
  59
  60 void put_online_cpus(void)
  61 {
  62         if (cpu_hotplug.active_writer == current)
  63                 return;
  64         mutex_lock(&cpu_hotplug.lock);
  65         if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  66                 wake_up_process(cpu_hotplug.active_writer);
  67         mutex_unlock(&cpu_hotplug.lock);
  68
  69 }
  70 EXPORT_SYMBOL_GPL(put_online_cpus);
  71
  72 #endif  /* CONFIG_HOTPLUG_CPU */
  73
  74 /*
  75  * The following two API's must be used when attempting
  76  * to serialize the updates to cpu_online_mask, cpu_present_mask.
  77  */
  78 void cpu_maps_update_begin(void)
  79 {
  80         mutex_lock(&cpu_add_remove_lock);
  81 }
  82
  83 void cpu_maps_update_done(void)
  84 {
  85         mutex_unlock(&cpu_add_remove_lock);
  86 }
  87
  88 /*
  89  * This ensures that the hotplug operation can begin only when the
  90  * refcount goes to zero.
  91  *
  92  * Note that during a cpu-hotplug operation, the new readers, if any,
  93  * will be blocked by the cpu_hotplug.lock
  94  *
  95  * Since cpu_hotplug_begin() is always called after invoking
  96  * cpu_maps_update_begin(), we can be sure that only one writer is active.
  97  *
  98  * Note that theoretically, there is a possibility of a livelock:
  99  * - Refcount goes to zero, last reader wakes up the sleeping
 100  *   writer.
 101  * - Last reader unlocks the cpu_hotplug.lock.
 102  * - A new reader arrives at this moment, bumps up the refcount.
 103  * - The writer acquires the cpu_hotplug.lock finds the refcount
 104  *   non zero and goes to sleep again.
 105  *
 106  * However, this is very difficult to achieve in practice since
 107  * get_online_cpus() not an api which is called all that often.
 108  *
 109  */
 110 static void cpu_hotplug_begin(void)
 111 {
 112         cpu_hotplug.active_writer = current;
 113
 114         for (;;) {
 115                 mutex_lock(&cpu_hotplug.lock);
 116                 if (likely(!cpu_hotplug.refcount))
 117                         break;
 118                 __set_current_state(TASK_UNINTERRUPTIBLE);
 119                 mutex_unlock(&cpu_hotplug.lock);
 120                 schedule();
 121         }
 122 }
 123
 124 static void cpu_hotplug_done(void)
 125 {
 126         cpu_hotplug.active_writer = NULL;
 127         mutex_unlock(&cpu_hotplug.lock);
 128 }
 129 /* Need to know about CPUs going up/down? */
 130 int __ref register_cpu_notifier(struct notifier_block *nb)
 131 {
 132         int ret;
 133         cpu_maps_update_begin();
 134         ret = raw_notifier_chain_register(&cpu_chain, nb);
 135         cpu_maps_update_done();
 136         return ret;
 137 }
 138
 139 #ifdef CONFIG_HOTPLUG_CPU
 140
 141 EXPORT_SYMBOL(register_cpu_notifier);
 142
 143 void __ref unregister_cpu_notifier(struct notifier_block *nb)
 144 {
 145         cpu_maps_update_begin();
 146         raw_notifier_chain_unregister(&cpu_chain, nb);
 147         cpu_maps_update_done();
 148 }
 149 EXPORT_SYMBOL(unregister_cpu_notifier);
 150
 151 static inline void check_for_tasks(int cpu)
 152 {
 153         struct task_struct *p;
 154
 155         write_lock_irq(&tasklist_lock);
 156         for_each_process(p) {
 157                 if (task_cpu(p) == cpu &&
 158                     (!cputime_eq(p->utime, cputime_zero) ||
 159                      !cputime_eq(p->stime, cputime_zero)))
 160                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 161                                 (state = %ld, flags = %x) \n",
 162                                  p->comm, task_pid_nr(p), cpu,
 163                                  p->state, p->flags);
 164         }
 165         write_unlock_irq(&tasklist_lock);
 166 }
 167
 168 struct take_cpu_down_param {
 169         unsigned long mod;
 170         void *hcpu;
 171 };
 172
 173 /* Take this CPU down. */
 174 static int __ref take_cpu_down(void *_param)
 175 {
 176         struct take_cpu_down_param *param = _param;
 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         /* Force idle task to run as soon as we yield: it should
 188            immediately notice cpu is offline and die quickly. */
 189         sched_idle_next();
 190         return 0;
 191 }
 192
 193 /* Requires cpu_add_remove_lock to be held */
 194 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 195 {
 196         int err, nr_calls = 0;
 197         cpumask_t old_allowed, tmp;
 198         void *hcpu = (void *)(long)cpu;
 199         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 200         struct take_cpu_down_param tcd_param = {
 201                 .mod = mod,
 202                 .hcpu = hcpu,
 203         };
 204
 205         if (num_online_cpus() == 1)
 206                 return -EBUSY;
 207
 208         if (!cpu_online(cpu))
 209                 return -EINVAL;
 210
 211         cpu_hotplug_begin();
 212         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 213                                         hcpu, -1, &nr_calls);
 214         if (err == NOTIFY_BAD) {
 215                 nr_calls--;
 216                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 217                                           hcpu, nr_calls, NULL);
 218                 printk("%s: attempt to take down CPU %u failed\n",
 219                                 __func__, cpu);
 220                 err = -EINVAL;
 221                 goto out_release;
 222         }
 223
 224         /* Ensure that we are not runnable on dying cpu */
 225         old_allowed = current->cpus_allowed;
 226         cpus_setall(tmp);
 227         cpu_clear(cpu, tmp);
 228         set_cpus_allowed_ptr(current, &tmp);
 229         tmp = cpumask_of_cpu(cpu);
 230
 231         err = __stop_machine(take_cpu_down, &tcd_param, &tmp);
 232         if (err) {
 233                 /* CPU didn't die: tell everyone.  Can't complain. */
 234                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 235                                             hcpu) == NOTIFY_BAD)
 236                         BUG();
 237
 238                 goto out_allowed;
 239         }
 240         BUG_ON(cpu_online(cpu));
 241
 242         /* Wait for it to sleep (leaving idle task). */
 243         while (!idle_cpu(cpu))
 244                 yield();
 245
 246         /* This actually kills the CPU. */
 247         __cpu_die(cpu);
 248
 249         /* CPU is completely dead: tell everyone.  Too late to complain. */
 250         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 251                                     hcpu) == NOTIFY_BAD)
 252                 BUG();
 253
 254         check_for_tasks(cpu);
 255
 256 out_allowed:
 257         set_cpus_allowed_ptr(current, &old_allowed);
 258 out_release:
 259         cpu_hotplug_done();
 260         if (!err) {
 261                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 262                                             hcpu) == NOTIFY_BAD)
 263                         BUG();
 264         }
 265         return err;
 266 }
 267
 268 int __ref cpu_down(unsigned int cpu)
 269 {
 270         int err = 0;
 271
 272         cpu_maps_update_begin();
 273
 274         if (cpu_hotplug_disabled) {
 275                 err = -EBUSY;
 276                 goto out;
 277         }
 278
 279         cpu_clear(cpu, cpu_active_map);
 280
 281         /*
 282          * Make sure the all cpus did the reschedule and are not
 283          * using stale version of the cpu_active_map.
 284          * This is not strictly necessary becuase stop_machine()
 285          * that we run down the line already provides the required
 286          * synchronization. But it's really a side effect and we do not
 287          * want to depend on the innards of the stop_machine here.
 288          */
 289         synchronize_sched();
 290
 291         err = _cpu_down(cpu, 0);
 292
 293         if (cpu_online(cpu))
 294                 cpu_set(cpu, cpu_active_map);
 295
 296 out:
 297         cpu_maps_update_done();
 298         return err;
 299 }
 300 EXPORT_SYMBOL(cpu_down);
 301 #endif /*CONFIG_HOTPLUG_CPU*/
 302
 303 /* Requires cpu_add_remove_lock to be held */
 304 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 305 {
 306         int ret, nr_calls = 0;
 307         void *hcpu = (void *)(long)cpu;
 308         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 309
 310         if (cpu_online(cpu) || !cpu_present(cpu))
 311                 return -EINVAL;
 312
 313         cpu_hotplug_begin();
 314         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 315                                                         -1, &nr_calls);
 316         if (ret == NOTIFY_BAD) {
 317                 nr_calls--;
 318                 printk("%s: attempt to bring up CPU %u failed\n",
 319                                 __func__, cpu);
 320                 ret = -EINVAL;
 321                 goto out_notify;
 322         }
 323
 324         /* Arch-specific enabling code. */
 325         ret = __cpu_up(cpu);
 326         if (ret != 0)
 327                 goto out_notify;
 328         BUG_ON(!cpu_online(cpu));
 329
 330         cpu_set(cpu, cpu_active_map);
 331
 332         /* Now call notifier in preparation. */
 333         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 334
 335 out_notify:
 336         if (ret != 0)
 337                 __raw_notifier_call_chain(&cpu_chain,
 338                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 339         cpu_hotplug_done();
 340
 341         return ret;
 342 }
 343
 344 int __cpuinit cpu_up(unsigned int cpu)
 345 {
 346         int err = 0;
 347         if (!cpu_isset(cpu, cpu_possible_map)) {
 348                 printk(KERN_ERR "can't online cpu %d because it is not "
 349                         "configured as may-hotadd at boot time\n", cpu);
 350 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
 351                 printk(KERN_ERR "please check additional_cpus= boot "
 352                                 "parameter\n");
 353 #endif
 354                 return -EINVAL;
 355         }
 356
 357         cpu_maps_update_begin();
 358
 359         if (cpu_hotplug_disabled) {
 360                 err = -EBUSY;
 361                 goto out;
 362         }
 363
 364         err = _cpu_up(cpu, 0);
 365
 366 out:
 367         cpu_maps_update_done();
 368         return err;
 369 }
 370
 371 #ifdef CONFIG_PM_SLEEP_SMP
 372 static cpumask_t frozen_cpus;
 373
 374 int disable_nonboot_cpus(void)
 375 {
 376         int cpu, first_cpu, error = 0;
 377
 378         cpu_maps_update_begin();
 379         first_cpu = first_cpu(cpu_online_map);
 380         /* We take down all of the non-boot CPUs in one shot to avoid races
 381          * with the userspace trying to use the CPU hotplug at the same time
 382          */
 383         cpus_clear(frozen_cpus);
 384         printk("Disabling non-boot CPUs ...\n");
 385         for_each_online_cpu(cpu) {
 386                 if (cpu == first_cpu)
 387                         continue;
 388                 error = _cpu_down(cpu, 1);
 389                 if (!error) {
 390                         cpu_set(cpu, frozen_cpus);
 391                         printk("CPU%d is down\n", cpu);
 392                 } else {
 393                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 394                                 cpu, error);
 395                         break;
 396                 }
 397         }
 398         if (!error) {
 399                 BUG_ON(num_online_cpus() > 1);
 400                 /* Make sure the CPUs won't be enabled by someone else */
 401                 cpu_hotplug_disabled = 1;
 402         } else {
 403                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 404         }
 405         cpu_maps_update_done();
 406         return error;
 407 }
 408
 409 void __ref enable_nonboot_cpus(void)
 410 {
 411         int cpu, error;
 412
 413         /* Allow everyone to use the CPU hotplug again */
 414         cpu_maps_update_begin();
 415         cpu_hotplug_disabled = 0;
 416         if (cpus_empty(frozen_cpus))
 417                 goto out;
 418
 419         printk("Enabling non-boot CPUs ...\n");
 420         for_each_cpu_mask_nr(cpu, frozen_cpus) {
 421                 error = _cpu_up(cpu, 1);
 422                 if (!error) {
 423                         printk("CPU%d is up\n", cpu);
 424                         continue;
 425                 }
 426                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 427         }
 428         cpus_clear(frozen_cpus);
 429 out:
 430         cpu_maps_update_done();
 431 }
 432 #endif /* CONFIG_PM_SLEEP_SMP */
 433
 434 /**
 435  * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
 436  * @cpu: cpu that just started
 437  *
 438  * This function calls the cpu_chain notifiers with CPU_STARTING.
 439  * It must be called by the arch code on the new cpu, before the new cpu
 440  * enables interrupts and before the "boot" cpu returns from __cpu_up().
 441  */
 442 void __cpuinit notify_cpu_starting(unsigned int cpu)
 443 {
 444         unsigned long val = CPU_STARTING;
 445
 446 #ifdef CONFIG_PM_SLEEP_SMP
 447         if (cpu_isset(cpu, frozen_cpus))
 448                 val = CPU_STARTING_FROZEN;
 449 #endif /* CONFIG_PM_SLEEP_SMP */
 450         raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
 451 }
 452
 453 #endif /* CONFIG_SMP */
 454
 455 /*
 456  * cpu_bit_bitmap[] is a special, "compressed" data structure that
 457  * represents all NR_CPUS bits binary values of 1<<nr.
 458  *
 459  * It is used by cpumask_of_cpu() to get a constant address to a CPU
 460  * mask value that has a single bit set only.
 461  */
 462
 463 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 464 #define MASK_DECLARE_1(x)       [x+1][0] = 1UL << (x)
 465 #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 466 #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 467 #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 468
 469 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 470
 471         MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
 472         MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 473 #if BITS_PER_LONG > 32
 474         MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
 475         MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 476 #endif
 477 };
 478 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 479
 480 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 481 EXPORT_SYMBOL(cpu_all_bits);
 482
 483 #ifdef CONFIG_INIT_ALL_POSSIBLE
 484 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
 485         = CPU_BITS_ALL;
 486 #else
 487 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
 488 #endif
 489 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
 490 EXPORT_SYMBOL(cpu_possible_mask);
 491
 492 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
 493 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
 494 EXPORT_SYMBOL(cpu_online_mask);
 495
 496 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
 497 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
 498 EXPORT_SYMBOL(cpu_present_mask);
 499
 500 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
 501 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
 502 EXPORT_SYMBOL(cpu_active_mask);
 503
 504 void set_cpu_possible(unsigned int cpu, bool possible)
 505 {
 506         if (possible)
 507                 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
 508         else
 509                 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
 510 }
 511
 512 void set_cpu_present(unsigned int cpu, bool present)
 513 {
 514         if (present)
 515                 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
 516         else
 517                 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
 518 }
 519
 520 void set_cpu_online(unsigned int cpu, bool online)
 521 {
 522         if (online)
 523                 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
 524         else
 525                 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
 526 }
 527
 528 void set_cpu_active(unsigned int cpu, bool active)
 529 {
 530         if (active)
 531                 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
 532         else
 533                 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
 534 }
 535
 536 void init_cpu_present(const struct cpumask *src)
 537 {
 538         cpumask_copy(to_cpumask(cpu_present_bits), src);
 539 }
 540
 541 void init_cpu_possible(const struct cpumask *src)
 542 {
 543         cpumask_copy(to_cpumask(cpu_possible_bits), src);
 544 }
 545
 546 void init_cpu_online(const struct cpumask *src)
 547 {
 548         cpumask_copy(to_cpumask(cpu_online_bits), src);
 549 }