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 EXPORT_SYMBOL_GPL(cpucontrol);
  21
  22 static struct notifier_block *cpu_chain;
  23
  24 /*
  25  * Used to check by callers if they need to acquire the cpucontrol
  26  * or not to protect a cpu from being removed. Its sometimes required to
  27  * call these functions both for normal operations, and in response to
  28  * a cpu being added/removed. If the context of the call is in the same
  29  * thread context as a CPU hotplug thread, we dont need to take the lock
  30  * since its already protected
  31  * check drivers/cpufreq/cpufreq.c for its usage - Ashok Raj
  32  */
  33
  34 int current_in_cpu_hotplug(void)
  35 {
  36         return (current->flags & PF_HOTPLUG_CPU);
  37 }
  38
  39 EXPORT_SYMBOL_GPL(current_in_cpu_hotplug);
  40
  41
  42 /* Need to know about CPUs going up/down? */
  43 int register_cpu_notifier(struct notifier_block *nb)
  44 {
  45         int ret;
  46
  47         if ((ret = down_interruptible(&cpucontrol)) != 0)
  48                 return ret;
  49         ret = notifier_chain_register(&cpu_chain, nb);
  50         up(&cpucontrol);
  51         return ret;
  52 }
  53 EXPORT_SYMBOL(register_cpu_notifier);
  54
  55 void unregister_cpu_notifier(struct notifier_block *nb)
  56 {
  57         down(&cpucontrol);
  58         notifier_chain_unregister(&cpu_chain, nb);
  59         up(&cpucontrol);
  60 }
  61 EXPORT_SYMBOL(unregister_cpu_notifier);
  62
  63 #ifdef CONFIG_HOTPLUG_CPU
  64 static inline void check_for_tasks(int cpu)
  65 {
  66         struct task_struct *p;
  67
  68         write_lock_irq(&tasklist_lock);
  69         for_each_process(p) {
  70                 if (task_cpu(p) == cpu &&
  71                     (!cputime_eq(p->utime, cputime_zero) ||
  72                      !cputime_eq(p->stime, cputime_zero)))
  73                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
  74                                 (state = %ld, flags = %lx) \n",
  75                                  p->comm, p->pid, cpu, p->state, p->flags);
  76         }
  77         write_unlock_irq(&tasklist_lock);
  78 }
  79
  80 /* Take this CPU down. */
  81 static int take_cpu_down(void *unused)
  82 {
  83         int err;
  84
  85         /* Ensure this CPU doesn't handle any more interrupts. */
  86         err = __cpu_disable();
  87         if (err < 0)
  88                 return err;
  89
  90         /* Force idle task to run as soon as we yield: it should
  91            immediately notice cpu is offline and die quickly. */
  92         sched_idle_next();
  93         return 0;
  94 }
  95
  96 int cpu_down(unsigned int cpu)
  97 {
  98         int err;
  99         struct task_struct *p;
 100         cpumask_t old_allowed, tmp;
 101
 102         if ((err = lock_cpu_hotplug_interruptible()) != 0)
 103                 return err;
 104
 105         if (num_online_cpus() == 1) {
 106                 err = -EBUSY;
 107                 goto out;
 108         }
 109
 110         if (!cpu_online(cpu)) {
 111                 err = -EINVAL;
 112                 goto out;
 113         }
 114
 115         /*
 116          * Leave a trace in current->flags indicating we are already in
 117          * process of performing CPU hotplug. Callers can check if cpucontrol
 118          * is already acquired by current thread, and if so not cause
 119          * a dead lock by not acquiring the lock
 120          */
 121         current->flags |= PF_HOTPLUG_CPU;
 122         err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
 123                                                 (void *)(long)cpu);
 124         if (err == NOTIFY_BAD) {
 125                 printk("%s: attempt to take down CPU %u failed\n",
 126                                 __FUNCTION__, cpu);
 127                 err = -EINVAL;
 128                 goto out;
 129         }
 130
 131         /* Ensure that we are not runnable on dying cpu */
 132         old_allowed = current->cpus_allowed;
 133         tmp = CPU_MASK_ALL;
 134         cpu_clear(cpu, tmp);
 135         set_cpus_allowed(current, tmp);
 136
 137         p = __stop_machine_run(take_cpu_down, NULL, cpu);
 138         if (IS_ERR(p)) {
 139                 /* CPU didn't die: tell everyone.  Can't complain. */
 140                 if (notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED,
 141                                 (void *)(long)cpu) == NOTIFY_BAD)
 142                         BUG();
 143
 144                 err = PTR_ERR(p);
 145                 goto out_allowed;
 146         }
 147
 148         if (cpu_online(cpu))
 149                 goto out_thread;
 150
 151         /* Wait for it to sleep (leaving idle task). */
 152         while (!idle_cpu(cpu))
 153                 yield();
 154
 155         /* This actually kills the CPU. */
 156         __cpu_die(cpu);
 157
 158         /* Move it here so it can run. */
 159         kthread_bind(p, get_cpu());
 160         put_cpu();
 161
 162         /* CPU is completely dead: tell everyone.  Too late to complain. */
 163         if (notifier_call_chain(&cpu_chain, CPU_DEAD, (void *)(long)cpu)
 164             == NOTIFY_BAD)
 165                 BUG();
 166
 167         check_for_tasks(cpu);
 168
 169 out_thread:
 170         err = kthread_stop(p);
 171 out_allowed:
 172         set_cpus_allowed(current, old_allowed);
 173 out:
 174         current->flags &= ~PF_HOTPLUG_CPU;
 175         unlock_cpu_hotplug();
 176         return err;
 177 }
 178 #endif /*CONFIG_HOTPLUG_CPU*/
 179
 180 int __devinit cpu_up(unsigned int cpu)
 181 {
 182         int ret;
 183         void *hcpu = (void *)(long)cpu;
 184
 185         if ((ret = down_interruptible(&cpucontrol)) != 0)
 186                 return ret;
 187
 188         if (cpu_online(cpu) || !cpu_present(cpu)) {
 189                 ret = -EINVAL;
 190                 goto out;
 191         }
 192
 193         /*
 194          * Leave a trace in current->flags indicating we are already in
 195          * process of performing CPU hotplug.
 196          */
 197         current->flags |= PF_HOTPLUG_CPU;
 198         ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
 199         if (ret == NOTIFY_BAD) {
 200                 printk("%s: attempt to bring up CPU %u failed\n",
 201                                 __FUNCTION__, cpu);
 202                 ret = -EINVAL;
 203                 goto out_notify;
 204         }
 205
 206         /* Arch-specific enabling code. */
 207         ret = __cpu_up(cpu);
 208         if (ret != 0)
 209                 goto out_notify;
 210         if (!cpu_online(cpu))
 211                 BUG();
 212
 213         /* Now call notifier in preparation. */
 214         notifier_call_chain(&cpu_chain, CPU_ONLINE, hcpu);
 215
 216 out_notify:
 217         if (ret != 0)
 218                 notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
 219 out:
 220         current->flags &= ~PF_HOTPLUG_CPU;
 221         up(&cpucontrol);
 222         return ret;
 223 }