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