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(cpucontrol);
  20
  21 static __cpuinitdata BLOCKING_NOTIFIER_HEAD(cpu_chain);
  22
  23 #ifdef CONFIG_HOTPLUG_CPU
  24 static struct task_struct *lock_cpu_hotplug_owner;
  25 static int lock_cpu_hotplug_depth;
  26
  27 static int __lock_cpu_hotplug(int interruptible)
  28 {
  29         int ret = 0;
  30
  31         if (lock_cpu_hotplug_owner != current) {
  32                 if (interruptible)
  33                         ret = mutex_lock_interruptible(&cpucontrol);
  34                 else
  35                         mutex_lock(&cpucontrol);
  36         }
  37
  38         /*
  39          * Set only if we succeed in locking
  40          */
  41         if (!ret) {
  42                 lock_cpu_hotplug_depth++;
  43                 lock_cpu_hotplug_owner = current;
  44         }
  45
  46         return ret;
  47 }
  48
  49 void lock_cpu_hotplug(void)
  50 {
  51         __lock_cpu_hotplug(0);
  52 }
  53 EXPORT_SYMBOL_GPL(lock_cpu_hotplug);
  54
  55 void unlock_cpu_hotplug(void)
  56 {
  57         if (--lock_cpu_hotplug_depth == 0) {
  58                 lock_cpu_hotplug_owner = NULL;
  59                 mutex_unlock(&cpucontrol);
  60         }
  61 }
  62 EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
  63
  64 int lock_cpu_hotplug_interruptible(void)
  65 {
  66         return __lock_cpu_hotplug(1);
  67 }
  68 EXPORT_SYMBOL_GPL(lock_cpu_hotplug_interruptible);
  69 #endif  /* CONFIG_HOTPLUG_CPU */
  70
  71 /* Need to know about CPUs going up/down? */
  72 int __cpuinit register_cpu_notifier(struct notifier_block *nb)
  73 {
  74         return blocking_notifier_chain_register(&cpu_chain, nb);
  75 }
  76
  77 #ifdef CONFIG_HOTPLUG_CPU
  78
  79 EXPORT_SYMBOL(register_cpu_notifier);
  80
  81 void unregister_cpu_notifier(struct notifier_block *nb)
  82 {
  83         blocking_notifier_chain_unregister(&cpu_chain, nb);
  84 }
  85 EXPORT_SYMBOL(unregister_cpu_notifier);
  86
  87 static inline void check_for_tasks(int cpu)
  88 {
  89         struct task_struct *p;
  90
  91         write_lock_irq(&tasklist_lock);
  92         for_each_process(p) {
  93                 if (task_cpu(p) == cpu &&
  94                     (!cputime_eq(p->utime, cputime_zero) ||
  95                      !cputime_eq(p->stime, cputime_zero)))
  96                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
  97                                 (state = %ld, flags = %lx) \n",
  98                                  p->comm, p->pid, cpu, p->state, p->flags);
  99         }
 100         write_unlock_irq(&tasklist_lock);
 101 }
 102
 103 /* Take this CPU down. */
 104 static int take_cpu_down(void *unused)
 105 {
 106         int err;
 107
 108         /* Ensure this CPU doesn't handle any more interrupts. */
 109         err = __cpu_disable();
 110         if (err < 0)
 111                 return err;
 112
 113         /* Force idle task to run as soon as we yield: it should
 114            immediately notice cpu is offline and die quickly. */
 115         sched_idle_next();
 116         return 0;
 117 }
 118
 119 int cpu_down(unsigned int cpu)
 120 {
 121         int err;
 122         struct task_struct *p;
 123         cpumask_t old_allowed, tmp;
 124
 125         if ((err = lock_cpu_hotplug_interruptible()) != 0)
 126                 return err;
 127
 128         if (num_online_cpus() == 1) {
 129                 err = -EBUSY;
 130                 goto out;
 131         }
 132
 133         if (!cpu_online(cpu)) {
 134                 err = -EINVAL;
 135                 goto out;
 136         }
 137
 138         err = blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
 139                                                 (void *)(long)cpu);
 140         if (err == NOTIFY_BAD) {
 141                 printk("%s: attempt to take down CPU %u failed\n",
 142                                 __FUNCTION__, cpu);
 143                 err = -EINVAL;
 144                 goto out;
 145         }
 146
 147         /* Ensure that we are not runnable on dying cpu */
 148         old_allowed = current->cpus_allowed;
 149         tmp = CPU_MASK_ALL;
 150         cpu_clear(cpu, tmp);
 151         set_cpus_allowed(current, tmp);
 152
 153         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 154         if (IS_ERR(p)) {
 155                 /* CPU didn't die: tell everyone.  Can't complain. */
 156                 if (blocking_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 157                                 (void *)(long)cpu) == NOTIFY_BAD)
 158                         BUG();
 159
 160                 err = PTR_ERR(p);
 161                 goto out_allowed;
 162         }
 163
 164         if (cpu_online(cpu))
 165                 goto out_thread;
 166
 167         /* Wait for it to sleep (leaving idle task). */
 168         while (!idle_cpu(cpu))
 169                 yield();
 170
 171         /* This actually kills the CPU. */
 172         __cpu_die(cpu);
 173
 174         /* Move it here so it can run. */
 175         kthread_bind(p, get_cpu());
 176         put_cpu();
 177
 178         /* CPU is completely dead: tell everyone.  Too late to complain. */
 179         if (blocking_notifier_call_chain(&cpu_chain, CPU_DEAD,
 180                         (void *)(long)cpu) == NOTIFY_BAD)
 181                 BUG();
 182
 183         check_for_tasks(cpu);
 184
 185 out_thread:
 186         err = kthread_stop(p);
 187 out_allowed:
 188         set_cpus_allowed(current, old_allowed);
 189 out:
 190         unlock_cpu_hotplug();
 191         return err;
 192 }
 193 #endif /*CONFIG_HOTPLUG_CPU*/
 194
 195 int __devinit cpu_up(unsigned int cpu)
 196 {
 197         int ret;
 198         void *hcpu = (void *)(long)cpu;
 199
 200         if ((ret = lock_cpu_hotplug_interruptible()) != 0)
 201                 return ret;
 202
 203         if (cpu_online(cpu) || !cpu_present(cpu)) {
 204                 ret = -EINVAL;
 205                 goto out;
 206         }
 207
 208         ret = blocking_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 209         if (ret == NOTIFY_BAD) {
 210                 printk("%s: attempt to bring up CPU %u failed\n",
 211                                 __FUNCTION__, cpu);
 212                 ret = -EINVAL;
 213                 goto out_notify;
 214         }
 215
 216         /* Arch-specific enabling code. */
 217         ret = __cpu_up(cpu);
 218         if (ret != 0)
 219                 goto out_notify;
 220         BUG_ON(!cpu_online(cpu));
 221
 222         /* Now call notifier in preparation. */
 223         blocking_notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 224
 225 out_notify:
 226         if (ret != 0)
 227                 blocking_notifier_call_chain(&cpu_chain,
 228                                 CPU_UP_CANCELED, hcpu);
 229 out:
 230         unlock_cpu_hotplug();
 231         return ret;
 232 }