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 <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         /* Ensure this CPU doesn't handle any more interrupts. */
  67         err = __cpu_disable();
  68         if (err < 0)
  69                 return err;
  70
  71         /* Force idle task to run as soon as we yield: it should
  72            immediately notice cpu is offline and die quickly. */
  73         sched_idle_next();
  74         return 0;
  75 }
  76
  77 int cpu_down(unsigned int cpu)
  78 {
  79         int err;
  80         struct task_struct *p;
  81         cpumask_t old_allowed, tmp;
  82
  83         if ((err = lock_cpu_hotplug_interruptible()) != 0)
  84                 return err;
  85
  86         if (num_online_cpus() == 1) {
  87                 err = -EBUSY;
  88                 goto out;
  89         }
  90
  91         if (!cpu_online(cpu)) {
  92                 err = -EINVAL;
  93                 goto out;
  94         }
  95
  96         err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
  97                                                 (void *)(long)cpu);
  98         if (err == NOTIFY_BAD) {
  99                 printk("%s: attempt to take down CPU %u failed\n",
 100                                 __FUNCTION__, cpu);
 101                 err = -EINVAL;
 102                 goto out;
 103         }
 104
 105         /* Ensure that we are not runnable on dying cpu */
 106         old_allowed = current->cpus_allowed;
 107         tmp = CPU_MASK_ALL;
 108         cpu_clear(cpu, tmp);
 109         set_cpus_allowed(current, tmp);
 110
 111         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 112         if (IS_ERR(p)) {
 113                 /* CPU didn't die: tell everyone.  Can't complain. */
 114                 if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 115                                 (void *)(long)cpu) == NOTIFY_BAD)
 116                         BUG();
 117
 118                 err = PTR_ERR(p);
 119                 goto out_allowed;
 120         }
 121
 122         if (cpu_online(cpu))
 123                 goto out_thread;
 124
 125         /* Wait for it to sleep (leaving idle task). */
 126         while (!idle_cpu(cpu))
 127                 yield();
 128
 129         /* This actually kills the CPU. */
 130         __cpu_die(cpu);
 131
 132         /* Move it here so it can run. */
 133         kthread_bind(p, get_cpu());
 134         put_cpu();
 135
 136         /* CPU is completely dead: tell everyone.  Too late to complain. */
 137         if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
 138             == NOTIFY_BAD)
 139                 BUG();
 140
 141         check_for_tasks(cpu);
 142
 143 out_thread:
 144         err = kthread_stop(p);
 145 out_allowed:
 146         set_cpus_allowed(current, old_allowed);
 147 out:
 148         unlock_cpu_hotplug();
 149         return err;
 150 }
 151 #endif /*CONFIG_HOTPLUG_CPU*/
 152
 153 int __devinit cpu_up(unsigned int cpu)
 154 {
 155         int ret;
 156         void *hcpu = (void *)(long)cpu;
 157
 158         if ((ret = down_interruptible(&cpucontrol)) != 0)
 159                 return ret;
 160
 161         if (cpu_online(cpu) || !cpu_present(cpu)) {
 162                 ret = -EINVAL;
 163                 goto out;
 164         }
 165         ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 166         if (ret == NOTIFY_BAD) {
 167                 printk("%s: attempt to bring up CPU %u failed\n",
 168                                 __FUNCTION__, cpu);
 169                 ret = -EINVAL;
 170                 goto out_notify;
 171         }
 172
 173         /* Arch-specific enabling code. */
 174         ret = __cpu_up(cpu);
 175         if (ret != 0)
 176                 goto out_notify;
 177         if (!cpu_online(cpu))
 178                 BUG();
 179
 180         /* Now call notifier in preparation. */
 181         notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 182
 183 out_notify:
 184         if (ret != 0)
 185                 notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
 186 out:
 187         up(&cpucontrol);
 188         return ret;
 189 }