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         struct task_struct *p;
 220         cpumask_t old_allowed, tmp;
 221         void *hcpu = (void *)(long)cpu;
 222         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 223         struct take_cpu_down_param tcd_param = {
 224                 .mod = mod,
 225                 .hcpu = hcpu,
 226         };
 227
 228         if (num_online_cpus() == 1)
 229                 return -EBUSY;
 230
 231         if (!cpu_online(cpu))
 232                 return -EINVAL;
 233
 234         cpu_hotplug_begin();
 235         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 236                                         hcpu, -1, &nr_calls);
 237         if (err == NOTIFY_BAD) {
 238                 nr_calls--;
 239                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 240                                           hcpu, nr_calls, NULL);
 241                 printk("%s: attempt to take down CPU %u failed\n",
 242                                 __func__, cpu);
 243                 err = -EINVAL;
 244                 goto out_release;
 245         }
 246
 247         /* Ensure that we are not runnable on dying cpu */
 248         old_allowed = current->cpus_allowed;
 249         cpus_setall(tmp);
 250         cpu_clear(cpu, tmp);
 251         set_cpus_allowed_ptr(current, &tmp);
 252
 253         p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
 254
 255         if (IS_ERR(p) || cpu_online(cpu)) {
 256                 /* CPU didn't die: tell everyone.  Can't complain. */
 257                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 258                                             hcpu) == NOTIFY_BAD)
 259                         BUG();
 260
 261                 if (IS_ERR(p)) {
 262                         err = PTR_ERR(p);
 263                         goto out_allowed;
 264                 }
 265                 goto out_thread;
 266         }
 267
 268         /* Wait for it to sleep (leaving idle task). */
 269         while (!idle_cpu(cpu))
 270                 yield();
 271
 272         /* This actually kills the CPU. */
 273         __cpu_die(cpu);
 274
 275         /* CPU is completely dead: tell everyone.  Too late to complain. */
 276         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 277                                     hcpu) == NOTIFY_BAD)
 278                 BUG();
 279
 280         check_for_tasks(cpu);
 281
 282 out_thread:
 283         err = kthread_stop(p);
 284 out_allowed:
 285         set_cpus_allowed_ptr(current, &old_allowed);
 286 out_release:
 287         cpu_hotplug_done();
 288         if (!err) {
 289                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 290                                             hcpu) == NOTIFY_BAD)
 291                         BUG();
 292         }
 293         return err;
 294 }
 295
 296 int __ref cpu_down(unsigned int cpu)
 297 {
 298         int err = 0;
 299
 300         cpu_maps_update_begin();
 301
 302         if (cpu_hotplug_disabled) {
 303                 err = -EBUSY;
 304                 goto out;
 305         }
 306
 307         cpu_clear(cpu, cpu_active_map);
 308
 309         /*
 310          * Make sure the all cpus did the reschedule and are not
 311          * using stale version of the cpu_active_map.
 312          * This is not strictly necessary becuase stop_machine()
 313          * that we run down the line already provides the required
 314          * synchronization. But it's really a side effect and we do not
 315          * want to depend on the innards of the stop_machine here.
 316          */
 317         synchronize_sched();
 318
 319         err = _cpu_down(cpu, 0);
 320
 321         if (cpu_online(cpu))
 322                 cpu_set(cpu, cpu_active_map);
 323
 324 out:
 325         cpu_maps_update_done();
 326         return err;
 327 }
 328 EXPORT_SYMBOL(cpu_down);
 329 #endif /*CONFIG_HOTPLUG_CPU*/
 330
 331 /* Requires cpu_add_remove_lock to be held */
 332 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 333 {
 334         int ret, nr_calls = 0;
 335         void *hcpu = (void *)(long)cpu;
 336         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 337
 338         if (cpu_online(cpu) || !cpu_present(cpu))
 339                 return -EINVAL;
 340
 341         cpu_hotplug_begin();
 342         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 343                                                         -1, &nr_calls);
 344         if (ret == NOTIFY_BAD) {
 345                 nr_calls--;
 346                 printk("%s: attempt to bring up CPU %u failed\n",
 347                                 __func__, cpu);
 348                 ret = -EINVAL;
 349                 goto out_notify;
 350         }
 351
 352         /* Arch-specific enabling code. */
 353         ret = __cpu_up(cpu);
 354         if (ret != 0)
 355                 goto out_notify;
 356         BUG_ON(!cpu_online(cpu));
 357
 358         /* Now call notifier in preparation. */
 359         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 360
 361 out_notify:
 362         if (ret != 0)
 363                 __raw_notifier_call_chain(&cpu_chain,
 364                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 365         cpu_hotplug_done();
 366
 367         return ret;
 368 }
 369
 370 int __cpuinit cpu_up(unsigned int cpu)
 371 {
 372         int err = 0;
 373         if (!cpu_isset(cpu, cpu_possible_map)) {
 374                 printk(KERN_ERR "can't online cpu %d because it is not "
 375                         "configured as may-hotadd at boot time\n", cpu);
 376 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
 377                 printk(KERN_ERR "please check additional_cpus= boot "
 378                                 "parameter\n");
 379 #endif
 380                 return -EINVAL;
 381         }
 382
 383         cpu_maps_update_begin();
 384
 385         if (cpu_hotplug_disabled) {
 386                 err = -EBUSY;
 387                 goto out;
 388         }
 389
 390         err = _cpu_up(cpu, 0);
 391
 392         if (cpu_online(cpu))
 393                 cpu_set(cpu, cpu_active_map);
 394
 395 out:
 396         cpu_maps_update_done();
 397         return err;
 398 }
 399
 400 #ifdef CONFIG_PM_SLEEP_SMP
 401 static cpumask_t frozen_cpus;
 402
 403 int disable_nonboot_cpus(void)
 404 {
 405         int cpu, first_cpu, error = 0;
 406
 407         cpu_maps_update_begin();
 408         first_cpu = first_cpu(cpu_online_map);
 409         /* We take down all of the non-boot CPUs in one shot to avoid races
 410          * with the userspace trying to use the CPU hotplug at the same time
 411          */
 412         cpus_clear(frozen_cpus);
 413         printk("Disabling non-boot CPUs ...\n");
 414         for_each_online_cpu(cpu) {
 415                 if (cpu == first_cpu)
 416                         continue;
 417                 error = _cpu_down(cpu, 1);
 418                 if (!error) {
 419                         cpu_set(cpu, frozen_cpus);
 420                         printk("CPU%d is down\n", cpu);
 421                 } else {
 422                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 423                                 cpu, error);
 424                         break;
 425                 }
 426         }
 427         if (!error) {
 428                 BUG_ON(num_online_cpus() > 1);
 429                 /* Make sure the CPUs won't be enabled by someone else */
 430                 cpu_hotplug_disabled = 1;
 431         } else {
 432                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 433         }
 434         cpu_maps_update_done();
 435         return error;
 436 }
 437
 438 void __ref enable_nonboot_cpus(void)
 439 {
 440         int cpu, error;
 441
 442         /* Allow everyone to use the CPU hotplug again */
 443         cpu_maps_update_begin();
 444         cpu_hotplug_disabled = 0;
 445         if (cpus_empty(frozen_cpus))
 446                 goto out;
 447
 448         printk("Enabling non-boot CPUs ...\n");
 449         for_each_cpu_mask_nr(cpu, frozen_cpus) {
 450                 error = _cpu_up(cpu, 1);
 451                 if (!error) {
 452                         printk("CPU%d is up\n", cpu);
 453                         continue;
 454                 }
 455                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 456         }
 457         cpus_clear(frozen_cpus);
 458 out:
 459         cpu_maps_update_done();
 460 }
 461 #endif /* CONFIG_PM_SLEEP_SMP */
 462
 463 #endif /* CONFIG_SMP */