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 /* Serializes the updates to cpu_online_map, cpu_present_map */
  19 static DEFINE_MUTEX(cpu_add_remove_lock);
  20
  21 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  22
  23 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  24  * Should always be manipulated under cpu_add_remove_lock
  25  */
  26 static int cpu_hotplug_disabled;
  27
  28 static struct {
  29         struct task_struct *active_writer;
  30         struct mutex lock; /* Synchronizes accesses to refcount, */
  31         /*
  32          * Also blocks the new readers during
  33          * an ongoing cpu hotplug operation.
  34          */
  35         int refcount;
  36 } cpu_hotplug;
  37
  38 void __init cpu_hotplug_init(void)
  39 {
  40         cpu_hotplug.active_writer = NULL;
  41         mutex_init(&cpu_hotplug.lock);
  42         cpu_hotplug.refcount = 0;
  43 }
  44
  45 #ifdef CONFIG_HOTPLUG_CPU
  46
  47 void get_online_cpus(void)
  48 {
  49         might_sleep();
  50         if (cpu_hotplug.active_writer == current)
  51                 return;
  52         mutex_lock(&cpu_hotplug.lock);
  53         cpu_hotplug.refcount++;
  54         mutex_unlock(&cpu_hotplug.lock);
  55
  56 }
  57 EXPORT_SYMBOL_GPL(get_online_cpus);
  58
  59 void put_online_cpus(void)
  60 {
  61         if (cpu_hotplug.active_writer == current)
  62                 return;
  63         mutex_lock(&cpu_hotplug.lock);
  64         if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  65                 wake_up_process(cpu_hotplug.active_writer);
  66         mutex_unlock(&cpu_hotplug.lock);
  67
  68 }
  69 EXPORT_SYMBOL_GPL(put_online_cpus);
  70
  71 #endif  /* CONFIG_HOTPLUG_CPU */
  72
  73 /*
  74  * The following two API's must be used when attempting
  75  * to serialize the updates to cpu_online_map, cpu_present_map.
  76  */
  77 void cpu_maps_update_begin(void)
  78 {
  79         mutex_lock(&cpu_add_remove_lock);
  80 }
  81
  82 void cpu_maps_update_done(void)
  83 {
  84         mutex_unlock(&cpu_add_remove_lock);
  85 }
  86
  87 /*
  88  * This ensures that the hotplug operation can begin only when the
  89  * refcount goes to zero.
  90  *
  91  * Note that during a cpu-hotplug operation, the new readers, if any,
  92  * will be blocked by the cpu_hotplug.lock
  93  *
  94  * Since cpu_hotplug_begin() is always called after invoking
  95  * cpu_maps_update_begin(), we can be sure that only one writer is active.
  96  *
  97  * Note that theoretically, there is a possibility of a livelock:
  98  * - Refcount goes to zero, last reader wakes up the sleeping
  99  *   writer.
 100  * - Last reader unlocks the cpu_hotplug.lock.
 101  * - A new reader arrives at this moment, bumps up the refcount.
 102  * - The writer acquires the cpu_hotplug.lock finds the refcount
 103  *   non zero and goes to sleep again.
 104  *
 105  * However, this is very difficult to achieve in practice since
 106  * get_online_cpus() not an api which is called all that often.
 107  *
 108  */
 109 static void cpu_hotplug_begin(void)
 110 {
 111         cpu_hotplug.active_writer = current;
 112
 113         for (;;) {
 114                 mutex_lock(&cpu_hotplug.lock);
 115                 if (likely(!cpu_hotplug.refcount))
 116                         break;
 117                 __set_current_state(TASK_UNINTERRUPTIBLE);
 118                 mutex_unlock(&cpu_hotplug.lock);
 119                 schedule();
 120         }
 121 }
 122
 123 static void cpu_hotplug_done(void)
 124 {
 125         cpu_hotplug.active_writer = NULL;
 126         mutex_unlock(&cpu_hotplug.lock);
 127 }
 128 /* Need to know about CPUs going up/down? */
 129 int __ref register_cpu_notifier(struct notifier_block *nb)
 130 {
 131         int ret;
 132         cpu_maps_update_begin();
 133         ret = raw_notifier_chain_register(&cpu_chain, nb);
 134         cpu_maps_update_done();
 135         return ret;
 136 }
 137
 138 #ifdef CONFIG_HOTPLUG_CPU
 139
 140 EXPORT_SYMBOL(register_cpu_notifier);
 141
 142 void __ref unregister_cpu_notifier(struct notifier_block *nb)
 143 {
 144         cpu_maps_update_begin();
 145         raw_notifier_chain_unregister(&cpu_chain, nb);
 146         cpu_maps_update_done();
 147 }
 148 EXPORT_SYMBOL(unregister_cpu_notifier);
 149
 150 static inline void check_for_tasks(int cpu)
 151 {
 152         struct task_struct *p;
 153
 154         write_lock_irq(&tasklist_lock);
 155         for_each_process(p) {
 156                 if (task_cpu(p) == cpu &&
 157                     (!cputime_eq(p->utime, cputime_zero) ||
 158                      !cputime_eq(p->stime, cputime_zero)))
 159                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 160                                 (state = %ld, flags = %x) \n",
 161                                  p->comm, task_pid_nr(p), cpu,
 162                                  p->state, p->flags);
 163         }
 164         write_unlock_irq(&tasklist_lock);
 165 }
 166
 167 struct take_cpu_down_param {
 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         int err;
 177
 178         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 179                                 param->hcpu);
 180         /* Ensure this CPU doesn't handle any more interrupts. */
 181         err = __cpu_disable();
 182         if (err < 0)
 183                 return err;
 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         struct task_struct *p;
 196         cpumask_t old_allowed, tmp;
 197         void *hcpu = (void *)(long)cpu;
 198         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 199         struct take_cpu_down_param tcd_param = {
 200                 .mod = mod,
 201                 .hcpu = hcpu,
 202         };
 203
 204         if (num_online_cpus() == 1)
 205                 return -EBUSY;
 206
 207         if (!cpu_online(cpu))
 208                 return -EINVAL;
 209
 210         cpu_hotplug_begin();
 211         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 212                                         hcpu, -1, &nr_calls);
 213         if (err == NOTIFY_BAD) {
 214                 nr_calls--;
 215                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 216                                           hcpu, nr_calls, NULL);
 217                 printk("%s: attempt to take down CPU %u failed\n",
 218                                 __func__, cpu);
 219                 err = -EINVAL;
 220                 goto out_release;
 221         }
 222
 223         /* Ensure that we are not runnable on dying cpu */
 224         old_allowed = current->cpus_allowed;
 225         cpus_setall(tmp);
 226         cpu_clear(cpu, tmp);
 227         set_cpus_allowed_ptr(current, &tmp);
 228
 229         p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
 230
 231         if (IS_ERR(p) || cpu_online(cpu)) {
 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                 if (IS_ERR(p)) {
 238                         err = PTR_ERR(p);
 239                         goto out_allowed;
 240                 }
 241                 goto out_thread;
 242         }
 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_thread:
 259         err = kthread_stop(p);
 260 out_allowed:
 261         set_cpus_allowed_ptr(current, &old_allowed);
 262 out_release:
 263         cpu_hotplug_done();
 264         return err;
 265 }
 266
 267 int __ref cpu_down(unsigned int cpu)
 268 {
 269         int err = 0;
 270
 271         cpu_maps_update_begin();
 272         if (cpu_hotplug_disabled)
 273                 err = -EBUSY;
 274         else
 275                 err = _cpu_down(cpu, 0);
 276
 277         cpu_maps_update_done();
 278         return err;
 279 }
 280 #endif /*CONFIG_HOTPLUG_CPU*/
 281
 282 /* Requires cpu_add_remove_lock to be held */
 283 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 284 {
 285         int ret, nr_calls = 0;
 286         void *hcpu = (void *)(long)cpu;
 287         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 288
 289         if (cpu_online(cpu) || !cpu_present(cpu))
 290                 return -EINVAL;
 291
 292         cpu_hotplug_begin();
 293         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 294                                                         -1, &nr_calls);
 295         if (ret == NOTIFY_BAD) {
 296                 nr_calls--;
 297                 printk("%s: attempt to bring up CPU %u failed\n",
 298                                 __func__, cpu);
 299                 ret = -EINVAL;
 300                 goto out_notify;
 301         }
 302
 303         /* Arch-specific enabling code. */
 304         ret = __cpu_up(cpu);
 305         if (ret != 0)
 306                 goto out_notify;
 307         BUG_ON(!cpu_online(cpu));
 308
 309         /* Now call notifier in preparation. */
 310         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 311
 312 out_notify:
 313         if (ret != 0)
 314                 __raw_notifier_call_chain(&cpu_chain,
 315                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 316         cpu_hotplug_done();
 317
 318         return ret;
 319 }
 320
 321 int __cpuinit cpu_up(unsigned int cpu)
 322 {
 323         int err = 0;
 324         if (!cpu_isset(cpu, cpu_possible_map)) {
 325                 printk(KERN_ERR "can't online cpu %d because it is not "
 326                         "configured as may-hotadd at boot time\n", cpu);
 327 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
 328                 printk(KERN_ERR "please check additional_cpus= boot "
 329                                 "parameter\n");
 330 #endif
 331                 return -EINVAL;
 332         }
 333
 334         cpu_maps_update_begin();
 335         if (cpu_hotplug_disabled)
 336                 err = -EBUSY;
 337         else
 338                 err = _cpu_up(cpu, 0);
 339
 340         cpu_maps_update_done();
 341         return err;
 342 }
 343
 344 #ifdef CONFIG_PM_SLEEP_SMP
 345 static cpumask_t frozen_cpus;
 346
 347 int disable_nonboot_cpus(void)
 348 {
 349         int cpu, first_cpu, error = 0;
 350
 351         cpu_maps_update_begin();
 352         first_cpu = first_cpu(cpu_online_map);
 353         /* We take down all of the non-boot CPUs in one shot to avoid races
 354          * with the userspace trying to use the CPU hotplug at the same time
 355          */
 356         cpus_clear(frozen_cpus);
 357         printk("Disabling non-boot CPUs ...\n");
 358         for_each_online_cpu(cpu) {
 359                 if (cpu == first_cpu)
 360                         continue;
 361                 error = _cpu_down(cpu, 1);
 362                 if (!error) {
 363                         cpu_set(cpu, frozen_cpus);
 364                         printk("CPU%d is down\n", cpu);
 365                 } else {
 366                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 367                                 cpu, error);
 368                         break;
 369                 }
 370         }
 371         if (!error) {
 372                 BUG_ON(num_online_cpus() > 1);
 373                 /* Make sure the CPUs won't be enabled by someone else */
 374                 cpu_hotplug_disabled = 1;
 375         } else {
 376                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 377         }
 378         cpu_maps_update_done();
 379         return error;
 380 }
 381
 382 void __ref enable_nonboot_cpus(void)
 383 {
 384         int cpu, error;
 385
 386         /* Allow everyone to use the CPU hotplug again */
 387         cpu_maps_update_begin();
 388         cpu_hotplug_disabled = 0;
 389         if (cpus_empty(frozen_cpus))
 390                 goto out;
 391
 392         printk("Enabling non-boot CPUs ...\n");
 393         for_each_cpu_mask(cpu, frozen_cpus) {
 394                 error = _cpu_up(cpu, 1);
 395                 if (!error) {
 396                         printk("CPU%d is up\n", cpu);
 397                         continue;
 398                 }
 399                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 400         }
 401         cpus_clear(frozen_cpus);
 402 out:
 403         cpu_maps_update_done();
 404 }
 405 #endif /* CONFIG_PM_SLEEP_SMP */