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