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 /* This protects CPUs going up and down... */
  19 static DEFINE_MUTEX(cpu_add_remove_lock);
  20 static DEFINE_MUTEX(cpu_bitmask_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 #ifdef CONFIG_HOTPLUG_CPU
  30
  31 /* Crappy recursive lock-takers in cpufreq! Complain loudly about idiots */
  32 static struct task_struct *recursive;
  33 static int recursive_depth;
  34
  35 void lock_cpu_hotplug(void)
  36 {
  37         struct task_struct *tsk = current;
  38
  39         if (tsk == recursive) {
  40                 static int warnings = 10;
  41                 if (warnings) {
  42                         printk(KERN_ERR "Lukewarm IQ detected in hotplug locking\n");
  43                         WARN_ON(1);
  44                         warnings--;
  45                 }
  46                 recursive_depth++;
  47                 return;
  48         }
  49         mutex_lock(&cpu_bitmask_lock);
  50         recursive = tsk;
  51 }
  52 EXPORT_SYMBOL_GPL(lock_cpu_hotplug);
  53
  54 void unlock_cpu_hotplug(void)
  55 {
  56         WARN_ON(recursive != current);
  57         if (recursive_depth) {
  58                 recursive_depth--;
  59                 return;
  60         }
  61         recursive = NULL;
  62         mutex_unlock(&cpu_bitmask_lock);
  63 }
  64 EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
  65
  66 #endif  /* CONFIG_HOTPLUG_CPU */
  67
  68 /* Need to know about CPUs going up/down? */
  69 int __cpuinit register_cpu_notifier(struct notifier_block *nb)
  70 {
  71         int ret;
  72         mutex_lock(&cpu_add_remove_lock);
  73         ret = raw_notifier_chain_register(&cpu_chain, nb);
  74         mutex_unlock(&cpu_add_remove_lock);
  75         return ret;
  76 }
  77
  78 #ifdef CONFIG_HOTPLUG_CPU
  79
  80 EXPORT_SYMBOL(register_cpu_notifier);
  81
  82 void unregister_cpu_notifier(struct notifier_block *nb)
  83 {
  84         mutex_lock(&cpu_add_remove_lock);
  85         raw_notifier_chain_unregister(&cpu_chain, nb);
  86         mutex_unlock(&cpu_add_remove_lock);
  87 }
  88 EXPORT_SYMBOL(unregister_cpu_notifier);
  89
  90 static inline void check_for_tasks(int cpu)
  91 {
  92         struct task_struct *p;
  93
  94         write_lock_irq(&tasklist_lock);
  95         for_each_process(p) {
  96                 if (task_cpu(p) == cpu &&
  97                     (!cputime_eq(p->utime, cputime_zero) ||
  98                      !cputime_eq(p->stime, cputime_zero)))
  99                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 100                                 (state = %ld, flags = %lx) \n",
 101                                  p->comm, p->pid, cpu, p->state, p->flags);
 102         }
 103         write_unlock_irq(&tasklist_lock);
 104 }
 105
 106 /* Take this CPU down. */
 107 static int take_cpu_down(void *unused)
 108 {
 109         int err;
 110
 111         /* Ensure this CPU doesn't handle any more interrupts. */
 112         err = __cpu_disable();
 113         if (err < 0)
 114                 return err;
 115
 116         /* Force idle task to run as soon as we yield: it should
 117            immediately notice cpu is offline and die quickly. */
 118         sched_idle_next();
 119         return 0;
 120 }
 121
 122 /* Requires cpu_add_remove_lock to be held */
 123 static int _cpu_down(unsigned int cpu)
 124 {
 125         int err;
 126         struct task_struct *p;
 127         cpumask_t old_allowed, tmp;
 128
 129         if (num_online_cpus() == 1)
 130                 return -EBUSY;
 131
 132         if (!cpu_online(cpu))
 133                 return -EINVAL;
 134
 135         err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
 136                                                 (void *)(long)cpu);
 137         if (err == NOTIFY_BAD) {
 138                 printk("%s: attempt to take down CPU %u failed\n",
 139                                 __FUNCTION__, cpu);
 140                 return -EINVAL;
 141         }
 142
 143         /* Ensure that we are not runnable on dying cpu */
 144         old_allowed = current->cpus_allowed;
 145         tmp = CPU_MASK_ALL;
 146         cpu_clear(cpu, tmp);
 147         set_cpus_allowed(current, tmp);
 148
 149         mutex_lock(&cpu_bitmask_lock);
 150         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 151         mutex_unlock(&cpu_bitmask_lock);
 152
 153         if (IS_ERR(p) || cpu_online(cpu)) {
 154                 /* CPU didn't die: tell everyone.  Can't complain. */
 155                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 156                                 (void *)(long)cpu) == NOTIFY_BAD)
 157                         BUG();
 158
 159                 if (IS_ERR(p)) {
 160                         err = PTR_ERR(p);
 161                         goto out_allowed;
 162                 }
 163                 goto out_thread;
 164         }
 165
 166         /* Wait for it to sleep (leaving idle task). */
 167         while (!idle_cpu(cpu))
 168                 yield();
 169
 170         /* This actually kills the CPU. */
 171         __cpu_die(cpu);
 172
 173         /* Move it here so it can run. */
 174         kthread_bind(p, get_cpu());
 175         put_cpu();
 176
 177         /* CPU is completely dead: tell everyone.  Too late to complain. */
 178         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD,
 179                         (void *)(long)cpu) == NOTIFY_BAD)
 180                 BUG();
 181
 182         check_for_tasks(cpu);
 183
 184 out_thread:
 185         err = kthread_stop(p);
 186 out_allowed:
 187         set_cpus_allowed(current, old_allowed);
 188         return err;
 189 }
 190
 191 int cpu_down(unsigned int cpu)
 192 {
 193         int err = 0;
 194
 195         mutex_lock(&cpu_add_remove_lock);
 196         if (cpu_hotplug_disabled)
 197                 err = -EBUSY;
 198         else
 199                 err = _cpu_down(cpu);
 200
 201         mutex_unlock(&cpu_add_remove_lock);
 202         return err;
 203 }
 204 #endif /*CONFIG_HOTPLUG_CPU*/
 205
 206 /* Requires cpu_add_remove_lock to be held */
 207 static int __cpuinit _cpu_up(unsigned int cpu)
 208 {
 209         int ret;
 210         void *hcpu = (void *)(long)cpu;
 211
 212         if (cpu_online(cpu) || !cpu_present(cpu))
 213                 return -EINVAL;
 214
 215         ret = raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 216         if (ret == NOTIFY_BAD) {
 217                 printk("%s: attempt to bring up CPU %u failed\n",
 218                                 __FUNCTION__, cpu);
 219                 ret = -EINVAL;
 220                 goto out_notify;
 221         }
 222
 223         /* Arch-specific enabling code. */
 224         mutex_lock(&cpu_bitmask_lock);
 225         ret = __cpu_up(cpu);
 226         mutex_unlock(&cpu_bitmask_lock);
 227         if (ret != 0)
 228                 goto out_notify;
 229         BUG_ON(!cpu_online(cpu));
 230
 231         /* Now call notifier in preparation. */
 232         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 233
 234 out_notify:
 235         if (ret != 0)
 236                 raw_notifier_call_chain(&cpu_chain,
 237                                 CPU_UP_CANCELED, hcpu);
 238
 239         return ret;
 240 }
 241
 242 int __cpuinit cpu_up(unsigned int cpu)
 243 {
 244         int err = 0;
 245
 246         mutex_lock(&cpu_add_remove_lock);
 247         if (cpu_hotplug_disabled)
 248                 err = -EBUSY;
 249         else
 250                 err = _cpu_up(cpu);
 251
 252         mutex_unlock(&cpu_add_remove_lock);
 253         return err;
 254 }
 255
 256 #ifdef CONFIG_SUSPEND_SMP
 257 static cpumask_t frozen_cpus;
 258
 259 int disable_nonboot_cpus(void)
 260 {
 261         int cpu, first_cpu, error = 0;
 262
 263         mutex_lock(&cpu_add_remove_lock);
 264         first_cpu = first_cpu(cpu_present_map);
 265         if (!cpu_online(first_cpu)) {
 266                 error = _cpu_up(first_cpu);
 267                 if (error) {
 268                         printk(KERN_ERR "Could not bring CPU%d up.\n",
 269                                 first_cpu);
 270                         goto out;
 271                 }
 272         }
 273
 274         /* We take down all of the non-boot CPUs in one shot to avoid races
 275          * with the userspace trying to use the CPU hotplug at the same time
 276          */
 277         cpus_clear(frozen_cpus);
 278         printk("Disabling non-boot CPUs ...\n");
 279         for_each_online_cpu(cpu) {
 280                 if (cpu == first_cpu)
 281                         continue;
 282                 error = _cpu_down(cpu);
 283                 if (!error) {
 284                         cpu_set(cpu, frozen_cpus);
 285                         printk("CPU%d is down\n", cpu);
 286                 } else {
 287                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 288                                 cpu, error);
 289                         break;
 290                 }
 291         }
 292         if (!error) {
 293                 BUG_ON(num_online_cpus() > 1);
 294                 /* Make sure the CPUs won't be enabled by someone else */
 295                 cpu_hotplug_disabled = 1;
 296         } else {
 297                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 298         }
 299 out:
 300         mutex_unlock(&cpu_add_remove_lock);
 301         return error;
 302 }
 303
 304 void enable_nonboot_cpus(void)
 305 {
 306         int cpu, error;
 307
 308         /* Allow everyone to use the CPU hotplug again */
 309         mutex_lock(&cpu_add_remove_lock);
 310         cpu_hotplug_disabled = 0;
 311         mutex_unlock(&cpu_add_remove_lock);
 312         if (cpus_empty(frozen_cpus))
 313                 return;
 314
 315         printk("Enabling non-boot CPUs ...\n");
 316         for_each_cpu_mask(cpu, frozen_cpus) {
 317                 error = cpu_up(cpu);
 318                 if (!error) {
 319                         printk("CPU%d is up\n", cpu);
 320                         continue;
 321                 }
 322                 printk(KERN_WARNING "Error taking CPU%d up: %d\n",
 323                         cpu, error);
 324         }
 325         cpus_clear(frozen_cpus);
 326 }
 327 #endif