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   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 <asm/semaphore.h>
  17
  18 /* This protects CPUs going up and down... */
  19 DECLARE_MUTEX(cpucontrol);
  20
  21 static struct notifier_block *cpu_chain;
  22
  23 /* Need to know about CPUs going up/down? */
  24 int register_cpu_notifier(struct notifier_block *nb)
  25 {
  26         int ret;
  27
  28         if ((ret = down_interruptible(&cpucontrol)) != 0)
  29                 return ret;
  30         ret = notifier_chain_register(&cpu_chain, nb);
  31         up(&cpucontrol);
  32         return ret;
  33 }
  34 EXPORT_SYMBOL(register_cpu_notifier);
  35
  36 void unregister_cpu_notifier(struct notifier_block *nb)
  37 {
  38         down(&cpucontrol);
  39         notifier_chain_unregister(&cpu_chain, nb);
  40         up(&cpucontrol);
  41 }
  42 EXPORT_SYMBOL(unregister_cpu_notifier);
  43
  44 #ifdef CONFIG_HOTPLUG_CPU
  45 static inline void check_for_tasks(int cpu)
  46 {
  47         struct task_struct *p;
  48
  49         write_lock_irq(&tasklist_lock);
  50         for_each_process(p) {
  51                 if (task_cpu(p) == cpu &&
  52                     (!cputime_eq(p->utime, cputime_zero) ||
  53                      !cputime_eq(p->stime, cputime_zero)))
  54                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
  55                                 (state = %ld, flags = %lx) \n",
  56                                  p->comm, p->pid, cpu, p->state, p->flags);
  57         }
  58         write_unlock_irq(&tasklist_lock);
  59 }
  60
  61 /* Take this CPU down. */
  62 static int take_cpu_down(void *unused)
  63 {
  64         int err;
  65
  66         /* Take offline: makes arch_cpu_down somewhat easier. */
  67         cpu_clear(smp_processor_id(), cpu_online_map);
  68
  69         /* Ensure this CPU doesn't handle any more interrupts. */
  70         err = __cpu_disable();
  71         if (err < 0)
  72                 cpu_set(smp_processor_id(), cpu_online_map);
  73         else
  74                 /* Force idle task to run as soon as we yield: it should
  75                    immediately notice cpu is offline and die quickly. */
  76                 sched_idle_next();
  77
  78         return err;
  79 }
  80
  81 int cpu_down(unsigned int cpu)
  82 {
  83         int err;
  84         struct task_struct *p;
  85         cpumask_t old_allowed, tmp;
  86
  87         if ((err = lock_cpu_hotplug_interruptible()) != 0)
  88                 return err;
  89
  90         if (num_online_cpus() == 1) {
  91                 err = -EBUSY;
  92                 goto out;
  93         }
  94
  95         if (!cpu_online(cpu)) {
  96                 err = -EINVAL;
  97                 goto out;
  98         }
  99
 100         err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
 101                                                 (void *)(long)cpu);
 102         if (err == NOTIFY_BAD) {
 103                 printk("%s: attempt to take down CPU %u failed\n",
 104                                 __FUNCTION__, cpu);
 105                 err = -EINVAL;
 106                 goto out;
 107         }
 108
 109         /* Ensure that we are not runnable on dying cpu */
 110         old_allowed = current->cpus_allowed;
 111         tmp = CPU_MASK_ALL;
 112         cpu_clear(cpu, tmp);
 113         set_cpus_allowed(current, tmp);
 114
 115         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 116         if (IS_ERR(p)) {
 117                 /* CPU didn't die: tell everyone.  Can't complain. */
 118                 if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 119                                 (void *)(long)cpu) == NOTIFY_BAD)
 120                         BUG();
 121
 122                 err = PTR_ERR(p);
 123                 goto out_allowed;
 124         }
 125
 126         if (cpu_online(cpu))
 127                 goto out_thread;
 128
 129         /* Wait for it to sleep (leaving idle task). */
 130         while (!idle_cpu(cpu))
 131                 yield();
 132
 133         /* This actually kills the CPU. */
 134         __cpu_die(cpu);
 135
 136         /* Move it here so it can run. */
 137         kthread_bind(p, get_cpu());
 138         put_cpu();
 139
 140         /* CPU is completely dead: tell everyone.  Too late to complain. */
 141         if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
 142             == NOTIFY_BAD)
 143                 BUG();
 144
 145         check_for_tasks(cpu);
 146
 147 out_thread:
 148         err = kthread_stop(p);
 149 out_allowed:
 150         set_cpus_allowed(current, old_allowed);
 151 out:
 152         unlock_cpu_hotplug();
 153         return err;
 154 }
 155 #endif /*CONFIG_HOTPLUG_CPU*/
 156
 157 int __devinit cpu_up(unsigned int cpu)
 158 {
 159         int ret;
 160         void *hcpu = (void *)(long)cpu;
 161
 162         if ((ret = down_interruptible(&cpucontrol)) != 0)
 163                 return ret;
 164
 165         if (cpu_online(cpu) || !cpu_present(cpu)) {
 166                 ret = -EINVAL;
 167                 goto out;
 168         }
 169         ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 170         if (ret == NOTIFY_BAD) {
 171                 printk("%s: attempt to bring up CPU %u failed\n",
 172                                 __FUNCTION__, cpu);
 173                 ret = -EINVAL;
 174                 goto out_notify;
 175         }
 176
 177         /* Arch-specific enabling code. */
 178         ret = __cpu_up(cpu);
 179         if (ret != 0)
 180                 goto out_notify;
 181         if (!cpu_online(cpu))
 182                 BUG();
 183
 184         /* Now call notifier in preparation. */
 185         notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 186
 187 out_notify:
 188         if (ret != 0)
 189                 notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
 190 out:
 191         up(&cpucontrol);
 192         return ret;
 193 }