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