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/kmod.h>         /* for hotplug_path */
  15 #include <linux/kthread.h>
  16 #include <linux/stop_machine.h>
  17 #include <asm/semaphore.h>
  18
  19 /* This protects CPUs going up and down... */
  20 DECLARE_MUTEX(cpucontrol);
  21
  22 static struct notifier_block *cpu_chain;
  23
  24 /* Need to know about CPUs going up/down? */
  25 int register_cpu_notifier(struct notifier_block *nb)
  26 {
  27         int ret;
  28
  29         if ((ret = down_interruptible(&cpucontrol)) != 0)
  30                 return ret;
  31         ret = notifier_chain_register(&cpu_chain, nb);
  32         up(&cpucontrol);
  33         return ret;
  34 }
  35 EXPORT_SYMBOL(register_cpu_notifier);
  36
  37 void unregister_cpu_notifier(struct notifier_block *nb)
  38 {
  39         down(&cpucontrol);
  40         notifier_chain_unregister(&cpu_chain, nb);
  41         up(&cpucontrol);
  42 }
  43 EXPORT_SYMBOL(unregister_cpu_notifier);
  44
  45 #ifdef CONFIG_HOTPLUG_CPU
  46 static inline void check_for_tasks(int cpu)
  47 {
  48         struct task_struct *p;
  49
  50         write_lock_irq(&tasklist_lock);
  51         for_each_process(p) {
  52                 if (task_cpu(p) == cpu && (p->utime != 0 || p->stime != 0))
  53                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
  54                                 (state = %ld, flags = %lx) \n",
  55                                  p->comm, p->pid, cpu, p->state, p->flags);
  56         }
  57         write_unlock_irq(&tasklist_lock);
  58 }
  59
  60 /* Notify userspace when a cpu event occurs, by running '/sbin/hotplug
  61  * cpu' with certain environment variables set.  */
  62 static int cpu_run_sbin_hotplug(unsigned int cpu, const char *action)
  63 {
  64         char *argv[3], *envp[6], cpu_str[12], action_str[32], devpath_str[40];
  65         int i;
  66
  67         sprintf(cpu_str, "CPU=%d", cpu);
  68         sprintf(action_str, "ACTION=%s", action);
  69         sprintf(devpath_str, "DEVPATH=devices/system/cpu/cpu%d", cpu);
  70
  71         i = 0;
  72         argv[i++] = hotplug_path;
  73         argv[i++] = "cpu";
  74         argv[i] = NULL;
  75
  76         i = 0;
  77         /* minimal command environment */
  78         envp[i++] = "HOME=/";
  79         envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
  80         envp[i++] = cpu_str;
  81         envp[i++] = action_str;
  82         envp[i++] = devpath_str;
  83         envp[i] = NULL;
  84
  85         return call_usermodehelper(argv[0], argv, envp, 0);
  86 }
  87
  88 /* Take this CPU down. */
  89 static int take_cpu_down(void *unused)
  90 {
  91         int err;
  92
  93         /* Take offline: makes arch_cpu_down somewhat easier. */
  94         cpu_clear(smp_processor_id(), cpu_online_map);
  95
  96         /* Ensure this CPU doesn't handle any more interrupts. */
  97         err = __cpu_disable();
  98         if (err < 0)
  99                 cpu_set(smp_processor_id(), cpu_online_map);
 100         else
 101                 /* Force idle task to run as soon as we yield: it should
 102                    immediately notice cpu is offline and die quickly. */
 103                 sched_idle_next();
 104
 105         return err;
 106 }
 107
 108 int cpu_down(unsigned int cpu)
 109 {
 110         int err;
 111         struct task_struct *p;
 112         cpumask_t old_allowed, tmp;
 113
 114         if ((err = lock_cpu_hotplug_interruptible()) != 0)
 115                 return err;
 116
 117         if (num_online_cpus() == 1) {
 118                 err = -EBUSY;
 119                 goto out;
 120         }
 121
 122         if (!cpu_online(cpu)) {
 123                 err = -EINVAL;
 124                 goto out;
 125         }
 126
 127         /* Ensure that we are not runnable on dying cpu */
 128         old_allowed = current->cpus_allowed;
 129         tmp = CPU_MASK_ALL;
 130         cpu_clear(cpu, tmp);
 131         set_cpus_allowed(current, tmp);
 132
 133         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 134         if (IS_ERR(p)) {
 135                 err = PTR_ERR(p);
 136                 goto out_allowed;
 137         }
 138
 139         if (cpu_online(cpu))
 140                 goto out_thread;
 141
 142         /* Wait for it to sleep (leaving idle task). */
 143         while (!idle_cpu(cpu))
 144                 yield();
 145
 146         /* This actually kills the CPU. */
 147         __cpu_die(cpu);
 148
 149         /* Move it here so it can run. */
 150         kthread_bind(p, smp_processor_id());
 151
 152         /* CPU is completely dead: tell everyone.  Too late to complain. */
 153         if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
 154             == NOTIFY_BAD)
 155                 BUG();
 156
 157         check_for_tasks(cpu);
 158
 159         cpu_run_sbin_hotplug(cpu, "offline");
 160
 161 out_thread:
 162         err = kthread_stop(p);
 163 out_allowed:
 164         set_cpus_allowed(current, old_allowed);
 165 out:
 166         unlock_cpu_hotplug();
 167         return err;
 168 }
 169 #else
 170 static inline int cpu_run_sbin_hotplug(unsigned int cpu, const char *action)
 171 {
 172         return 0;
 173 }
 174 #endif /*CONFIG_HOTPLUG_CPU*/
 175
 176 int __devinit cpu_up(unsigned int cpu)
 177 {
 178         int ret;
 179         void *hcpu = (void *)(long)cpu;
 180
 181         if ((ret = down_interruptible(&cpucontrol)) != 0)
 182                 return ret;
 183
 184         if (cpu_online(cpu) || !cpu_present(cpu)) {
 185                 ret = -EINVAL;
 186                 goto out;
 187         }
 188         ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 189         if (ret == NOTIFY_BAD) {
 190                 printk("%s: attempt to bring up CPU %u failed\n",
 191                                 __FUNCTION__, cpu);
 192                 ret = -EINVAL;
 193                 goto out_notify;
 194         }
 195
 196         /* Arch-specific enabling code. */
 197         ret = __cpu_up(cpu);
 198         if (ret != 0)
 199                 goto out_notify;
 200         if (!cpu_online(cpu))
 201                 BUG();
 202
 203         /* Now call notifier in preparation. */
 204         notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 205
 206 out_notify:
 207         if (ret != 0)
 208                 notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
 209 out:
 210         up(&cpucontrol);
 211         return ret;
 212 }