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 struct notifier_block *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         int ret;
  75
  76         if ((ret = lock_cpu_hotplug_interruptible()) != 0)
  77                 return ret;
  78         ret = notifier_chain_register(&cpu_chain, nb);
  79         unlock_cpu_hotplug();
  80         return ret;
  81 }
  82 EXPORT_SYMBOL(register_cpu_notifier);
  83
  84 void unregister_cpu_notifier(struct notifier_block *nb)
  85 {
  86         lock_cpu_hotplug();
  87         notifier_chain_unregister(&cpu_chain, nb);
  88         unlock_cpu_hotplug();
  89 }
  90 EXPORT_SYMBOL(unregister_cpu_notifier);
  91
  92 #ifdef CONFIG_HOTPLUG_CPU
  93 static inline void check_for_tasks(int cpu)
  94 {
  95         struct task_struct *p;
  96
  97         write_lock_irq(&tasklist_lock);
  98         for_each_process(p) {
  99                 if (task_cpu(p) == cpu &&
 100                     (!cputime_eq(p->utime, cputime_zero) ||
 101                      !cputime_eq(p->stime, cputime_zero)))
 102                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 103                                 (state = %ld, flags = %lx) \n",
 104                                  p->comm, p->pid, cpu, p->state, p->flags);
 105         }
 106         write_unlock_irq(&tasklist_lock);
 107 }
 108
 109 /* Take this CPU down. */
 110 static int take_cpu_down(void *unused)
 111 {
 112         int err;
 113
 114         /* Ensure this CPU doesn't handle any more interrupts. */
 115         err = __cpu_disable();
 116         if (err < 0)
 117                 return err;
 118
 119         /* Force idle task to run as soon as we yield: it should
 120            immediately notice cpu is offline and die quickly. */
 121         sched_idle_next();
 122         return 0;
 123 }
 124
 125 int cpu_down(unsigned int cpu)
 126 {
 127         int err;
 128         struct task_struct *p;
 129         cpumask_t old_allowed, tmp;
 130
 131         if ((err = lock_cpu_hotplug_interruptible()) != 0)
 132                 return err;
 133
 134         if (num_online_cpus() == 1) {
 135                 err = -EBUSY;
 136                 goto out;
 137         }
 138
 139         if (!cpu_online(cpu)) {
 140                 err = -EINVAL;
 141                 goto out;
 142         }
 143
 144         err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
 145                                                 (void *)(long)cpu);
 146         if (err == NOTIFY_BAD) {
 147                 printk("%s: attempt to take down CPU %u failed\n",
 148                                 __FUNCTION__, cpu);
 149                 err = -EINVAL;
 150                 goto out;
 151         }
 152
 153         /* Ensure that we are not runnable on dying cpu */
 154         old_allowed = current->cpus_allowed;
 155         tmp = CPU_MASK_ALL;
 156         cpu_clear(cpu, tmp);
 157         set_cpus_allowed(current, tmp);
 158
 159         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 160         if (IS_ERR(p)) {
 161                 /* CPU didn't die: tell everyone.  Can't complain. */
 162                 if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 163                                 (void *)(long)cpu) == NOTIFY_BAD)
 164                         BUG();
 165
 166                 err = PTR_ERR(p);
 167                 goto out_allowed;
 168         }
 169
 170         if (cpu_online(cpu))
 171                 goto out_thread;
 172
 173         /* Wait for it to sleep (leaving idle task). */
 174         while (!idle_cpu(cpu))
 175                 yield();
 176
 177         /* This actually kills the CPU. */
 178         __cpu_die(cpu);
 179
 180         /* Move it here so it can run. */
 181         kthread_bind(p, get_cpu());
 182         put_cpu();
 183
 184         /* CPU is completely dead: tell everyone.  Too late to complain. */
 185         if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
 186             == NOTIFY_BAD)
 187                 BUG();
 188
 189         check_for_tasks(cpu);
 190
 191 out_thread:
 192         err = kthread_stop(p);
 193 out_allowed:
 194         set_cpus_allowed(current, old_allowed);
 195 out:
 196         unlock_cpu_hotplug();
 197         return err;
 198 }
 199 #endif /*CONFIG_HOTPLUG_CPU*/
 200
 201 int __devinit cpu_up(unsigned int cpu)
 202 {
 203         int ret;
 204         void *hcpu = (void *)(long)cpu;
 205
 206         if ((ret = lock_cpu_hotplug_interruptible()) != 0)
 207                 return ret;
 208
 209         if (cpu_online(cpu) || !cpu_present(cpu)) {
 210                 ret = -EINVAL;
 211                 goto out;
 212         }
 213
 214         ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 215         if (ret == NOTIFY_BAD) {
 216                 printk("%s: attempt to bring up CPU %u failed\n",
 217                                 __FUNCTION__, cpu);
 218                 ret = -EINVAL;
 219                 goto out_notify;
 220         }
 221
 222         /* Arch-specific enabling code. */
 223         ret = __cpu_up(cpu);
 224         if (ret != 0)
 225                 goto out_notify;
 226         if (!cpu_online(cpu))
 227                 BUG();
 228
 229         /* Now call notifier in preparation. */
 230         notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 231
 232 out_notify:
 233         if (ret != 0)
 234                 notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
 235 out:
 236         unlock_cpu_hotplug();
 237         return ret;
 238 }