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 /*
  19  * Represents all cpu's present in the system
  20  * In systems capable of hotplug, this map could dynamically grow
  21  * as new cpu's are detected in the system via any platform specific
  22  * method, such as ACPI for e.g.
  23  */
  24 cpumask_t cpu_present_map __read_mostly;
  25 EXPORT_SYMBOL(cpu_present_map);
  26
  27 #ifndef CONFIG_SMP
  28
  29 /*
  30  * Represents all cpu's that are currently online.
  31  */
  32 cpumask_t cpu_online_map __read_mostly = CPU_MASK_ALL;
  33 EXPORT_SYMBOL(cpu_online_map);
  34
  35 cpumask_t cpu_possible_map __read_mostly = CPU_MASK_ALL;
  36 EXPORT_SYMBOL(cpu_possible_map);
  37
  38 #else /* CONFIG_SMP */
  39
  40 /* Serializes the updates to cpu_online_map, cpu_present_map */
  41 static DEFINE_MUTEX(cpu_add_remove_lock);
  42
  43 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  44
  45 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  46  * Should always be manipulated under cpu_add_remove_lock
  47  */
  48 static int cpu_hotplug_disabled;
  49
  50 static struct {
  51         struct task_struct *active_writer;
  52         struct mutex lock; /* Synchronizes accesses to refcount, */
  53         /*
  54          * Also blocks the new readers during
  55          * an ongoing cpu hotplug operation.
  56          */
  57         int refcount;
  58 } cpu_hotplug;
  59
  60 void __init cpu_hotplug_init(void)
  61 {
  62         cpu_hotplug.active_writer = NULL;
  63         mutex_init(&cpu_hotplug.lock);
  64         cpu_hotplug.refcount = 0;
  65 }
  66
  67 cpumask_t cpu_active_map;
  68
  69 #ifdef CONFIG_HOTPLUG_CPU
  70
  71 void get_online_cpus(void)
  72 {
  73         might_sleep();
  74         if (cpu_hotplug.active_writer == current)
  75                 return;
  76         mutex_lock(&cpu_hotplug.lock);
  77         cpu_hotplug.refcount++;
  78         mutex_unlock(&cpu_hotplug.lock);
  79
  80 }
  81 EXPORT_SYMBOL_GPL(get_online_cpus);
  82
  83 void put_online_cpus(void)
  84 {
  85         if (cpu_hotplug.active_writer == current)
  86                 return;
  87         mutex_lock(&cpu_hotplug.lock);
  88         if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  89                 wake_up_process(cpu_hotplug.active_writer);
  90         mutex_unlock(&cpu_hotplug.lock);
  91
  92 }
  93 EXPORT_SYMBOL_GPL(put_online_cpus);
  94
  95 #endif  /* CONFIG_HOTPLUG_CPU */
  96
  97 /*
  98  * The following two API's must be used when attempting
  99  * to serialize the updates to cpu_online_map, cpu_present_map.
 100  */
 101 void cpu_maps_update_begin(void)
 102 {
 103         mutex_lock(&cpu_add_remove_lock);
 104 }
 105
 106 void cpu_maps_update_done(void)
 107 {
 108         mutex_unlock(&cpu_add_remove_lock);
 109 }
 110
 111 /*
 112  * This ensures that the hotplug operation can begin only when the
 113  * refcount goes to zero.
 114  *
 115  * Note that during a cpu-hotplug operation, the new readers, if any,
 116  * will be blocked by the cpu_hotplug.lock
 117  *
 118  * Since cpu_hotplug_begin() is always called after invoking
 119  * cpu_maps_update_begin(), we can be sure that only one writer is active.
 120  *
 121  * Note that theoretically, there is a possibility of a livelock:
 122  * - Refcount goes to zero, last reader wakes up the sleeping
 123  *   writer.
 124  * - Last reader unlocks the cpu_hotplug.lock.
 125  * - A new reader arrives at this moment, bumps up the refcount.
 126  * - The writer acquires the cpu_hotplug.lock finds the refcount
 127  *   non zero and goes to sleep again.
 128  *
 129  * However, this is very difficult to achieve in practice since
 130  * get_online_cpus() not an api which is called all that often.
 131  *
 132  */
 133 static void cpu_hotplug_begin(void)
 134 {
 135         cpu_hotplug.active_writer = current;
 136
 137         for (;;) {
 138                 mutex_lock(&cpu_hotplug.lock);
 139                 if (likely(!cpu_hotplug.refcount))
 140                         break;
 141                 __set_current_state(TASK_UNINTERRUPTIBLE);
 142                 mutex_unlock(&cpu_hotplug.lock);
 143                 schedule();
 144         }
 145 }
 146
 147 static void cpu_hotplug_done(void)
 148 {
 149         cpu_hotplug.active_writer = NULL;
 150         mutex_unlock(&cpu_hotplug.lock);
 151 }
 152 /* Need to know about CPUs going up/down? */
 153 int __ref register_cpu_notifier(struct notifier_block *nb)
 154 {
 155         int ret;
 156         cpu_maps_update_begin();
 157         ret = raw_notifier_chain_register(&cpu_chain, nb);
 158         cpu_maps_update_done();
 159         return ret;
 160 }
 161
 162 #ifdef CONFIG_HOTPLUG_CPU
 163
 164 EXPORT_SYMBOL(register_cpu_notifier);
 165
 166 void __ref unregister_cpu_notifier(struct notifier_block *nb)
 167 {
 168         cpu_maps_update_begin();
 169         raw_notifier_chain_unregister(&cpu_chain, nb);
 170         cpu_maps_update_done();
 171 }
 172 EXPORT_SYMBOL(unregister_cpu_notifier);
 173
 174 static inline void check_for_tasks(int cpu)
 175 {
 176         struct task_struct *p;
 177
 178         write_lock_irq(&tasklist_lock);
 179         for_each_process(p) {
 180                 if (task_cpu(p) == cpu &&
 181                     (!cputime_eq(p->utime, cputime_zero) ||
 182                      !cputime_eq(p->stime, cputime_zero)))
 183                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 184                                 (state = %ld, flags = %x) \n",
 185                                  p->comm, task_pid_nr(p), cpu,
 186                                  p->state, p->flags);
 187         }
 188         write_unlock_irq(&tasklist_lock);
 189 }
 190
 191 struct take_cpu_down_param {
 192         unsigned long mod;
 193         void *hcpu;
 194 };
 195
 196 /* Take this CPU down. */
 197 static int __ref take_cpu_down(void *_param)
 198 {
 199         struct take_cpu_down_param *param = _param;
 200         int err;
 201
 202         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 203                                 param->hcpu);
 204         /* Ensure this CPU doesn't handle any more interrupts. */
 205         err = __cpu_disable();
 206         if (err < 0)
 207                 return err;
 208
 209         /* Force idle task to run as soon as we yield: it should
 210            immediately notice cpu is offline and die quickly. */
 211         sched_idle_next();
 212         return 0;
 213 }
 214
 215 /* Requires cpu_add_remove_lock to be held */
 216 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 217 {
 218         int err, nr_calls = 0;
 219         cpumask_t old_allowed, tmp;
 220         void *hcpu = (void *)(long)cpu;
 221         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 222         struct take_cpu_down_param tcd_param = {
 223                 .mod = mod,
 224                 .hcpu = hcpu,
 225         };
 226
 227         if (num_online_cpus() == 1)
 228                 return -EBUSY;
 229
 230         if (!cpu_online(cpu))
 231                 return -EINVAL;
 232
 233         cpu_hotplug_begin();
 234         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 235                                         hcpu, -1, &nr_calls);
 236         if (err == NOTIFY_BAD) {
 237                 nr_calls--;
 238                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 239                                           hcpu, nr_calls, NULL);
 240                 printk("%s: attempt to take down CPU %u failed\n",
 241                                 __func__, cpu);
 242                 err = -EINVAL;
 243                 goto out_release;
 244         }
 245
 246         /* Ensure that we are not runnable on dying cpu */
 247         old_allowed = current->cpus_allowed;
 248         cpus_setall(tmp);
 249         cpu_clear(cpu, tmp);
 250         set_cpus_allowed_ptr(current, &tmp);
 251
 252         err = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
 253
 254         if (err || cpu_online(cpu)) {
 255                 /* CPU didn't die: tell everyone.  Can't complain. */
 256                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 257                                             hcpu) == NOTIFY_BAD)
 258                         BUG();
 259
 260                 goto out_allowed;
 261         }
 262
 263         /* Wait for it to sleep (leaving idle task). */
 264         while (!idle_cpu(cpu))
 265                 yield();
 266
 267         /* This actually kills the CPU. */
 268         __cpu_die(cpu);
 269
 270         /* CPU is completely dead: tell everyone.  Too late to complain. */
 271         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 272                                     hcpu) == NOTIFY_BAD)
 273                 BUG();
 274
 275         check_for_tasks(cpu);
 276
 277 out_allowed:
 278         set_cpus_allowed_ptr(current, &old_allowed);
 279 out_release:
 280         cpu_hotplug_done();
 281         if (!err) {
 282                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 283                                             hcpu) == NOTIFY_BAD)
 284                         BUG();
 285         }
 286         return err;
 287 }
 288
 289 int __ref cpu_down(unsigned int cpu)
 290 {
 291         int err = 0;
 292
 293         cpu_maps_update_begin();
 294
 295         if (cpu_hotplug_disabled) {
 296                 err = -EBUSY;
 297                 goto out;
 298         }
 299
 300         cpu_clear(cpu, cpu_active_map);
 301
 302         /*
 303          * Make sure the all cpus did the reschedule and are not
 304          * using stale version of the cpu_active_map.
 305          * This is not strictly necessary becuase stop_machine()
 306          * that we run down the line already provides the required
 307          * synchronization. But it's really a side effect and we do not
 308          * want to depend on the innards of the stop_machine here.
 309          */
 310         synchronize_sched();
 311
 312         err = _cpu_down(cpu, 0);
 313
 314         if (cpu_online(cpu))
 315                 cpu_set(cpu, cpu_active_map);
 316
 317 out:
 318         cpu_maps_update_done();
 319         return err;
 320 }
 321 EXPORT_SYMBOL(cpu_down);
 322 #endif /*CONFIG_HOTPLUG_CPU*/
 323
 324 /* Requires cpu_add_remove_lock to be held */
 325 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 326 {
 327         int ret, nr_calls = 0;
 328         void *hcpu = (void *)(long)cpu;
 329         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 330
 331         if (cpu_online(cpu) || !cpu_present(cpu))
 332                 return -EINVAL;
 333
 334         cpu_hotplug_begin();
 335         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 336                                                         -1, &nr_calls);
 337         if (ret == NOTIFY_BAD) {
 338                 nr_calls--;
 339                 printk("%s: attempt to bring up CPU %u failed\n",
 340                                 __func__, cpu);
 341                 ret = -EINVAL;
 342                 goto out_notify;
 343         }
 344
 345         /* Arch-specific enabling code. */
 346         ret = __cpu_up(cpu);
 347         if (ret != 0)
 348                 goto out_notify;
 349         BUG_ON(!cpu_online(cpu));
 350
 351         /* Now call notifier in preparation. */
 352         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 353
 354 out_notify:
 355         if (ret != 0)
 356                 __raw_notifier_call_chain(&cpu_chain,
 357                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 358         cpu_hotplug_done();
 359
 360         return ret;
 361 }
 362
 363 int __cpuinit cpu_up(unsigned int cpu)
 364 {
 365         int err = 0;
 366         if (!cpu_isset(cpu, cpu_possible_map)) {
 367                 printk(KERN_ERR "can't online cpu %d because it is not "
 368                         "configured as may-hotadd at boot time\n", cpu);
 369 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
 370                 printk(KERN_ERR "please check additional_cpus= boot "
 371                                 "parameter\n");
 372 #endif
 373                 return -EINVAL;
 374         }
 375
 376         cpu_maps_update_begin();
 377
 378         if (cpu_hotplug_disabled) {
 379                 err = -EBUSY;
 380                 goto out;
 381         }
 382
 383         err = _cpu_up(cpu, 0);
 384
 385         if (cpu_online(cpu))
 386                 cpu_set(cpu, cpu_active_map);
 387
 388 out:
 389         cpu_maps_update_done();
 390         return err;
 391 }
 392
 393 #ifdef CONFIG_PM_SLEEP_SMP
 394 static cpumask_t frozen_cpus;
 395
 396 int disable_nonboot_cpus(void)
 397 {
 398         int cpu, first_cpu, error = 0;
 399
 400         cpu_maps_update_begin();
 401         first_cpu = first_cpu(cpu_online_map);
 402         /* We take down all of the non-boot CPUs in one shot to avoid races
 403          * with the userspace trying to use the CPU hotplug at the same time
 404          */
 405         cpus_clear(frozen_cpus);
 406         printk("Disabling non-boot CPUs ...\n");
 407         for_each_online_cpu(cpu) {
 408                 if (cpu == first_cpu)
 409                         continue;
 410                 error = _cpu_down(cpu, 1);
 411                 if (!error) {
 412                         cpu_set(cpu, frozen_cpus);
 413                         printk("CPU%d is down\n", cpu);
 414                 } else {
 415                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 416                                 cpu, error);
 417                         break;
 418                 }
 419         }
 420         if (!error) {
 421                 BUG_ON(num_online_cpus() > 1);
 422                 /* Make sure the CPUs won't be enabled by someone else */
 423                 cpu_hotplug_disabled = 1;
 424         } else {
 425                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 426         }
 427         cpu_maps_update_done();
 428         return error;
 429 }
 430
 431 void __ref enable_nonboot_cpus(void)
 432 {
 433         int cpu, error;
 434
 435         /* Allow everyone to use the CPU hotplug again */
 436         cpu_maps_update_begin();
 437         cpu_hotplug_disabled = 0;
 438         if (cpus_empty(frozen_cpus))
 439                 goto out;
 440
 441         printk("Enabling non-boot CPUs ...\n");
 442         for_each_cpu_mask_nr(cpu, frozen_cpus) {
 443                 error = _cpu_up(cpu, 1);
 444                 if (!error) {
 445                         printk("CPU%d is up\n", cpu);
 446                         continue;
 447                 }
 448                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 449         }
 450         cpus_clear(frozen_cpus);
 451 out:
 452         cpu_maps_update_done();
 453 }
 454 #endif /* CONFIG_PM_SLEEP_SMP */
 455
 456 #endif /* CONFIG_SMP */