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         unsigned long mod;
 168         void *hcpu;
 169 };
 170
 171 /* Take this CPU down. */
 172 static int __ref take_cpu_down(void *_param)
 173 {
 174         struct take_cpu_down_param *param = _param;
 175         int err;
 176
 177         /* Ensure this CPU doesn't handle any more interrupts. */
 178         err = __cpu_disable();
 179         if (err < 0)
 180                 return err;
 181
 182         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 183                                 param->hcpu);
 184
 185         /* Force idle task to run as soon as we yield: it should
 186            immediately notice cpu is offline and die quickly. */
 187         sched_idle_next();
 188         return 0;
 189 }
 190
 191 /* Requires cpu_add_remove_lock to be held */
 192 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 193 {
 194         int err, nr_calls = 0;
 195         cpumask_var_t old_allowed;
 196         void *hcpu = (void *)(long)cpu;
 197         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 198         struct take_cpu_down_param tcd_param = {
 199                 .mod = mod,
 200                 .hcpu = hcpu,
 201         };
 202
 203         if (num_online_cpus() == 1)
 204                 return -EBUSY;
 205
 206         if (!cpu_online(cpu))
 207                 return -EINVAL;
 208
 209         if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
 210                 return -ENOMEM;
 211
 212         cpu_hotplug_begin();
 213         set_cpu_active(cpu, false);
 214         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 215                                         hcpu, -1, &nr_calls);
 216         if (err == NOTIFY_BAD) {
 217                 set_cpu_active(cpu, true);
 218
 219                 nr_calls--;
 220                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 221                                           hcpu, nr_calls, NULL);
 222                 printk("%s: attempt to take down CPU %u failed\n",
 223                                 __func__, cpu);
 224                 err = -EINVAL;
 225                 goto out_release;
 226         }
 227
 228         /* Ensure that we are not runnable on dying cpu */
 229         cpumask_copy(old_allowed, &current->cpus_allowed);
 230         set_cpus_allowed_ptr(current, cpu_active_mask);
 231
 232         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
 233         if (err) {
 234                 set_cpu_active(cpu, true);
 235                 /* CPU didn't die: tell everyone.  Can't complain. */
 236                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 237                                             hcpu) == NOTIFY_BAD)
 238                         BUG();
 239
 240                 goto out_allowed;
 241         }
 242         BUG_ON(cpu_online(cpu));
 243
 244         /* Wait for it to sleep (leaving idle task). */
 245         while (!idle_cpu(cpu))
 246                 yield();
 247
 248         /* This actually kills the CPU. */
 249         __cpu_die(cpu);
 250
 251         /* CPU is completely dead: tell everyone.  Too late to complain. */
 252         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 253                                     hcpu) == NOTIFY_BAD)
 254                 BUG();
 255
 256         check_for_tasks(cpu);
 257
 258 out_allowed:
 259         set_cpus_allowed_ptr(current, old_allowed);
 260 out_release:
 261         cpu_hotplug_done();
 262         if (!err) {
 263                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 264                                             hcpu) == NOTIFY_BAD)
 265                         BUG();
 266         }
 267         free_cpumask_var(old_allowed);
 268         return err;
 269 }
 270
 271 int __ref cpu_down(unsigned int cpu)
 272 {
 273         int err;
 274
 275         err = stop_machine_create();
 276         if (err)
 277                 return err;
 278         cpu_maps_update_begin();
 279
 280         if (cpu_hotplug_disabled) {
 281                 err = -EBUSY;
 282                 goto out;
 283         }
 284
 285         err = _cpu_down(cpu, 0);
 286
 287 out:
 288         cpu_maps_update_done();
 289         stop_machine_destroy();
 290         return err;
 291 }
 292 EXPORT_SYMBOL(cpu_down);
 293 #endif /*CONFIG_HOTPLUG_CPU*/
 294
 295 /* Requires cpu_add_remove_lock to be held */
 296 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 297 {
 298         int ret, nr_calls = 0;
 299         void *hcpu = (void *)(long)cpu;
 300         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 301
 302         if (cpu_online(cpu) || !cpu_present(cpu))
 303                 return -EINVAL;
 304
 305         cpu_hotplug_begin();
 306         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 307                                                         -1, &nr_calls);
 308         if (ret == NOTIFY_BAD) {
 309                 nr_calls--;
 310                 printk("%s: attempt to bring up CPU %u failed\n",
 311                                 __func__, cpu);
 312                 ret = -EINVAL;
 313                 goto out_notify;
 314         }
 315
 316         /* Arch-specific enabling code. */
 317         ret = __cpu_up(cpu);
 318         if (ret != 0)
 319                 goto out_notify;
 320         BUG_ON(!cpu_online(cpu));
 321
 322         set_cpu_active(cpu, true);
 323
 324         /* Now call notifier in preparation. */
 325         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 326
 327 out_notify:
 328         if (ret != 0)
 329                 __raw_notifier_call_chain(&cpu_chain,
 330                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 331         cpu_hotplug_done();
 332
 333         return ret;
 334 }
 335
 336 int __cpuinit cpu_up(unsigned int cpu)
 337 {
 338         int err = 0;
 339         if (!cpu_possible(cpu)) {
 340                 printk(KERN_ERR "can't online cpu %d because it is not "
 341                         "configured as may-hotadd at boot time\n", cpu);
 342 #if defined(CONFIG_IA64)
 343                 printk(KERN_ERR "please check additional_cpus= boot "
 344                                 "parameter\n");
 345 #endif
 346                 return -EINVAL;
 347         }
 348
 349         cpu_maps_update_begin();
 350
 351         if (cpu_hotplug_disabled) {
 352                 err = -EBUSY;
 353                 goto out;
 354         }
 355
 356         err = _cpu_up(cpu, 0);
 357
 358 out:
 359         cpu_maps_update_done();
 360         return err;
 361 }
 362
 363 #ifdef CONFIG_PM_SLEEP_SMP
 364 static cpumask_var_t frozen_cpus;
 365
 366 int disable_nonboot_cpus(void)
 367 {
 368         int cpu, first_cpu, error;
 369
 370         error = stop_machine_create();
 371         if (error)
 372                 return error;
 373         cpu_maps_update_begin();
 374         first_cpu = cpumask_first(cpu_online_mask);
 375         /*
 376          * We take down all of the non-boot CPUs in one shot to avoid races
 377          * with the userspace trying to use the CPU hotplug at the same time
 378          */
 379         cpumask_clear(frozen_cpus);
 380
 381         printk("Disabling non-boot CPUs ...\n");
 382         for_each_online_cpu(cpu) {
 383                 if (cpu == first_cpu)
 384                         continue;
 385                 error = _cpu_down(cpu, 1);
 386                 if (!error)
 387                         cpumask_set_cpu(cpu, frozen_cpus);
 388                 else {
 389                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 390                                 cpu, error);
 391                         break;
 392                 }
 393         }
 394
 395         if (!error) {
 396                 BUG_ON(num_online_cpus() > 1);
 397                 /* Make sure the CPUs won't be enabled by someone else */
 398                 cpu_hotplug_disabled = 1;
 399         } else {
 400                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 401         }
 402         cpu_maps_update_done();
 403         stop_machine_destroy();
 404         return error;
 405 }
 406
 407 void __weak arch_enable_nonboot_cpus_begin(void)
 408 {
 409 }
 410
 411 void __weak arch_enable_nonboot_cpus_end(void)
 412 {
 413 }
 414
 415 void __ref enable_nonboot_cpus(void)
 416 {
 417         int cpu, error;
 418
 419         /* Allow everyone to use the CPU hotplug again */
 420         cpu_maps_update_begin();
 421         cpu_hotplug_disabled = 0;
 422         if (cpumask_empty(frozen_cpus))
 423                 goto out;
 424
 425         printk("Enabling non-boot CPUs ...\n");
 426
 427         arch_enable_nonboot_cpus_begin();
 428
 429         for_each_cpu(cpu, frozen_cpus) {
 430                 error = _cpu_up(cpu, 1);
 431                 if (!error) {
 432                         printk("CPU%d is up\n", cpu);
 433                         continue;
 434                 }
 435                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 436         }
 437
 438         arch_enable_nonboot_cpus_end();
 439
 440         cpumask_clear(frozen_cpus);
 441 out:
 442         cpu_maps_update_done();
 443 }
 444
 445 static int alloc_frozen_cpus(void)
 446 {
 447         if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
 448                 return -ENOMEM;
 449         return 0;
 450 }
 451 core_initcall(alloc_frozen_cpus);
 452 #endif /* CONFIG_PM_SLEEP_SMP */
 453
 454 /**
 455  * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
 456  * @cpu: cpu that just started
 457  *
 458  * This function calls the cpu_chain notifiers with CPU_STARTING.
 459  * It must be called by the arch code on the new cpu, before the new cpu
 460  * enables interrupts and before the "boot" cpu returns from __cpu_up().
 461  */
 462 void __cpuinit notify_cpu_starting(unsigned int cpu)
 463 {
 464         unsigned long val = CPU_STARTING;
 465
 466 #ifdef CONFIG_PM_SLEEP_SMP
 467         if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
 468                 val = CPU_STARTING_FROZEN;
 469 #endif /* CONFIG_PM_SLEEP_SMP */
 470         raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
 471 }
 472
 473 #endif /* CONFIG_SMP */
 474
 475 /*
 476  * cpu_bit_bitmap[] is a special, "compressed" data structure that
 477  * represents all NR_CPUS bits binary values of 1<<nr.
 478  *
 479  * It is used by cpumask_of() to get a constant address to a CPU
 480  * mask value that has a single bit set only.
 481  */
 482
 483 /* cpu_bit_bitmap[0] is empty - so we can back into it */
 484 #define MASK_DECLARE_1(x)       [x+1][0] = 1UL << (x)
 485 #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 486 #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 487 #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 488
 489 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 490
 491         MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
 492         MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 493 #if BITS_PER_LONG > 32
 494         MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
 495         MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 496 #endif
 497 };
 498 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 499
 500 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 501 EXPORT_SYMBOL(cpu_all_bits);
 502
 503 #ifdef CONFIG_INIT_ALL_POSSIBLE
 504 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
 505         = CPU_BITS_ALL;
 506 #else
 507 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
 508 #endif
 509 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
 510 EXPORT_SYMBOL(cpu_possible_mask);
 511
 512 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
 513 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
 514 EXPORT_SYMBOL(cpu_online_mask);
 515
 516 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
 517 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
 518 EXPORT_SYMBOL(cpu_present_mask);
 519
 520 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
 521 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
 522 EXPORT_SYMBOL(cpu_active_mask);
 523
 524 void set_cpu_possible(unsigned int cpu, bool possible)
 525 {
 526         if (possible)
 527                 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
 528         else
 529                 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
 530 }
 531
 532 void set_cpu_present(unsigned int cpu, bool present)
 533 {
 534         if (present)
 535                 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
 536         else
 537                 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
 538 }
 539
 540 void set_cpu_online(unsigned int cpu, bool online)
 541 {
 542         if (online)
 543                 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
 544         else
 545                 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
 546 }
 547
 548 void set_cpu_active(unsigned int cpu, bool active)
 549 {
 550         if (active)
 551                 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
 552         else
 553                 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
 554 }
 555
 556 void init_cpu_present(const struct cpumask *src)
 557 {
 558         cpumask_copy(to_cpumask(cpu_present_bits), src);
 559 }
 560
 561 void init_cpu_possible(const struct cpumask *src)
 562 {
 563         cpumask_copy(to_cpumask(cpu_possible_bits), src);
 564 }
 565
 566 void init_cpu_online(const struct cpumask *src)
 567 {
 568         cpumask_copy(to_cpumask(cpu_online_bits), src);
 569 }