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 = %x) \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, int tasks_frozen)
 124 {
 125         int err, nr_calls = 0;
 126         struct task_struct *p;
 127         cpumask_t old_allowed, tmp;
 128         void *hcpu = (void *)(long)cpu;
 129         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 130
 131         if (num_online_cpus() == 1)
 132                 return -EBUSY;
 133
 134         if (!cpu_online(cpu))
 135                 return -EINVAL;
 136
 137         raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
 138         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 139                                         hcpu, -1, &nr_calls);
 140         if (err == NOTIFY_BAD) {
 141                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 142                                           hcpu, nr_calls, NULL);
 143                 printk("%s: attempt to take down CPU %u failed\n",
 144                                 __FUNCTION__, cpu);
 145                 err = -EINVAL;
 146                 goto out_release;
 147         }
 148
 149         /* Ensure that we are not runnable on dying cpu */
 150         old_allowed = current->cpus_allowed;
 151         tmp = CPU_MASK_ALL;
 152         cpu_clear(cpu, tmp);
 153         set_cpus_allowed(current, tmp);
 154
 155         mutex_lock(&cpu_bitmask_lock);
 156         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 157         mutex_unlock(&cpu_bitmask_lock);
 158
 159         if (IS_ERR(p) || cpu_online(cpu)) {
 160                 /* CPU didn't die: tell everyone.  Can't complain. */
 161                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 162                                             hcpu) == NOTIFY_BAD)
 163                         BUG();
 164
 165                 if (IS_ERR(p)) {
 166                         err = PTR_ERR(p);
 167                         goto out_allowed;
 168                 }
 169                 goto out_thread;
 170         }
 171
 172         /* Wait for it to sleep (leaving idle task). */
 173         while (!idle_cpu(cpu))
 174                 yield();
 175
 176         /* This actually kills the CPU. */
 177         __cpu_die(cpu);
 178
 179         /* CPU is completely dead: tell everyone.  Too late to complain. */
 180         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 181                                     hcpu) == NOTIFY_BAD)
 182                 BUG();
 183
 184         check_for_tasks(cpu);
 185
 186 out_thread:
 187         err = kthread_stop(p);
 188 out_allowed:
 189         set_cpus_allowed(current, old_allowed);
 190 out_release:
 191         raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
 192         return err;
 193 }
 194
 195 int cpu_down(unsigned int cpu)
 196 {
 197         int err = 0;
 198
 199         mutex_lock(&cpu_add_remove_lock);
 200         if (cpu_hotplug_disabled)
 201                 err = -EBUSY;
 202         else
 203                 err = _cpu_down(cpu, 0);
 204
 205         mutex_unlock(&cpu_add_remove_lock);
 206         return err;
 207 }
 208 #endif /*CONFIG_HOTPLUG_CPU*/
 209
 210 /* Requires cpu_add_remove_lock to be held */
 211 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 212 {
 213         int ret, nr_calls = 0;
 214         void *hcpu = (void *)(long)cpu;
 215         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 216
 217         if (cpu_online(cpu) || !cpu_present(cpu))
 218                 return -EINVAL;
 219
 220         raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
 221         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 222                                                         -1, &nr_calls);
 223         if (ret == NOTIFY_BAD) {
 224                 printk("%s: attempt to bring up CPU %u failed\n",
 225                                 __FUNCTION__, cpu);
 226                 ret = -EINVAL;
 227                 goto out_notify;
 228         }
 229
 230         /* Arch-specific enabling code. */
 231         mutex_lock(&cpu_bitmask_lock);
 232         ret = __cpu_up(cpu);
 233         mutex_unlock(&cpu_bitmask_lock);
 234         if (ret != 0)
 235                 goto out_notify;
 236         BUG_ON(!cpu_online(cpu));
 237
 238         /* Now call notifier in preparation. */
 239         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 240
 241 out_notify:
 242         if (ret != 0)
 243                 __raw_notifier_call_chain(&cpu_chain,
 244                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 245         raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
 246
 247         return ret;
 248 }
 249
 250 int __cpuinit cpu_up(unsigned int cpu)
 251 {
 252         int err = 0;
 253
 254         mutex_lock(&cpu_add_remove_lock);
 255         if (cpu_hotplug_disabled)
 256                 err = -EBUSY;
 257         else
 258                 err = _cpu_up(cpu, 0);
 259
 260         mutex_unlock(&cpu_add_remove_lock);
 261         return err;
 262 }
 263
 264 #ifdef CONFIG_SUSPEND_SMP
 265 static cpumask_t frozen_cpus;
 266
 267 int disable_nonboot_cpus(void)
 268 {
 269         int cpu, first_cpu, error = 0;
 270
 271         mutex_lock(&cpu_add_remove_lock);
 272         first_cpu = first_cpu(cpu_online_map);
 273         /* We take down all of the non-boot CPUs in one shot to avoid races
 274          * with the userspace trying to use the CPU hotplug at the same time
 275          */
 276         cpus_clear(frozen_cpus);
 277         printk("Disabling non-boot CPUs ...\n");
 278         for_each_online_cpu(cpu) {
 279                 if (cpu == first_cpu)
 280                         continue;
 281                 error = _cpu_down(cpu, 1);
 282                 if (!error) {
 283                         cpu_set(cpu, frozen_cpus);
 284                         printk("CPU%d is down\n", cpu);
 285                 } else {
 286                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
 287                                 cpu, error);
 288                         break;
 289                 }
 290         }
 291         if (!error) {
 292                 BUG_ON(num_online_cpus() > 1);
 293                 /* Make sure the CPUs won't be enabled by someone else */
 294                 cpu_hotplug_disabled = 1;
 295         } else {
 296                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 297         }
 298         mutex_unlock(&cpu_add_remove_lock);
 299         return error;
 300 }
 301
 302 void enable_nonboot_cpus(void)
 303 {
 304         int cpu, error;
 305
 306         /* Allow everyone to use the CPU hotplug again */
 307         mutex_lock(&cpu_add_remove_lock);
 308         cpu_hotplug_disabled = 0;
 309         if (cpus_empty(frozen_cpus))
 310                 goto out;
 311
 312         printk("Enabling non-boot CPUs ...\n");
 313         for_each_cpu_mask(cpu, frozen_cpus) {
 314                 error = _cpu_up(cpu, 1);
 315                 if (!error) {
 316                         printk("CPU%d is up\n", cpu);
 317                         continue;
 318                 }
 319                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 320         }
 321         cpus_clear(frozen_cpus);
 322 out:
 323         mutex_unlock(&cpu_add_remove_lock);
 324 }
 325 #endif