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|
/* CPU control.
* (C) 2001, 2002, 2003, 2004 Rusty Russell
*
* This code is licenced under the GPL.
*/
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <linux/mutex.h>
#ifdef CONFIG_SMP
/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);
static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
* Should always be manipulated under cpu_add_remove_lock
*/
static int cpu_hotplug_disabled;
static struct {
struct task_struct *active_writer;
struct mutex lock; /* Synchronizes accesses to refcount, */
/*
* Also blocks the new readers during
* an ongoing cpu hotplug operation.
*/
int refcount;
} cpu_hotplug = {
.active_writer = NULL,
.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
.refcount = 0,
};
#ifdef CONFIG_HOTPLUG_CPU
void get_online_cpus(void)
{
might_sleep();
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
cpu_hotplug.refcount++;
mutex_unlock(&cpu_hotplug.lock);
}
EXPORT_SYMBOL_GPL(get_online_cpus);
void put_online_cpus(void)
{
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
wake_up_process(cpu_hotplug.active_writer);
mutex_unlock(&cpu_hotplug.lock);
}
EXPORT_SYMBOL_GPL(put_online_cpus);
#endif /* CONFIG_HOTPLUG_CPU */
/*
* The following two API's must be used when attempting
* to serialize the updates to cpu_online_mask, cpu_present_mask.
*/
void cpu_maps_update_begin(void)
{
mutex_lock(&cpu_add_remove_lock);
}
void cpu_maps_update_done(void)
{
mutex_unlock(&cpu_add_remove_lock);
}
/*
* This ensures that the hotplug operation can begin only when the
* refcount goes to zero.
*
* Note that during a cpu-hotplug operation, the new readers, if any,
* will be blocked by the cpu_hotplug.lock
*
* Since cpu_hotplug_begin() is always called after invoking
* cpu_maps_update_begin(), we can be sure that only one writer is active.
*
* Note that theoretically, there is a possibility of a livelock:
* - Refcount goes to zero, last reader wakes up the sleeping
* writer.
* - Last reader unlocks the cpu_hotplug.lock.
* - A new reader arrives at this moment, bumps up the refcount.
* - The writer acquires the cpu_hotplug.lock finds the refcount
* non zero and goes to sleep again.
*
* However, this is very difficult to achieve in practice since
* get_online_cpus() not an api which is called all that often.
*
*/
static void cpu_hotplug_begin(void)
{
cpu_hotplug.active_writer = current;
for (;;) {
mutex_lock(&cpu_hotplug.lock);
if (likely(!cpu_hotplug.refcount))
break;
__set_current_state(TASK_UNINTERRUPTIBLE);
mutex_unlock(&cpu_hotplug.lock);
schedule();
}
}
static void cpu_hotplug_done(void)
{
cpu_hotplug.active_writer = NULL;
mutex_unlock(&cpu_hotplug.lock);
}
/* Need to know about CPUs going up/down? */
int __ref register_cpu_notifier(struct notifier_block *nb)
{
int ret;
cpu_maps_update_begin();
ret = raw_notifier_chain_register(&cpu_chain, nb);
cpu_maps_update_done();
return ret;
}
#ifdef CONFIG_HOTPLUG_CPU
EXPORT_SYMBOL(register_cpu_notifier);
void __ref unregister_cpu_notifier(struct notifier_block *nb)
{
cpu_maps_update_begin();
raw_notifier_chain_unregister(&cpu_chain, nb);
cpu_maps_update_done();
}
EXPORT_SYMBOL(unregister_cpu_notifier);
static inline void check_for_tasks(int cpu)
{
struct task_struct *p;
write_lock_irq(&tasklist_lock);
for_each_process(p) {
if (task_cpu(p) == cpu &&
(!cputime_eq(p->utime, cputime_zero) ||
!cputime_eq(p->stime, cputime_zero)))
printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
(state = %ld, flags = %x) \n",
p->comm, task_pid_nr(p), cpu,
p->state, p->flags);
}
write_unlock_irq(&tasklist_lock);
}
struct take_cpu_down_param {
unsigned long mod;
void *hcpu;
};
/* Take this CPU down. */
static int __ref take_cpu_down(void *_param)
{
struct take_cpu_down_param *param = _param;
int err;
/* Ensure this CPU doesn't handle any more interrupts. */
err = __cpu_disable();
if (err < 0)
return err;
raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
param->hcpu);
/* Force idle task to run as soon as we yield: it should
immediately notice cpu is offline and die quickly. */
sched_idle_next();
return 0;
}
/* Requires cpu_add_remove_lock to be held */
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
{
int err, nr_calls = 0;
cpumask_var_t old_allowed;
void *hcpu = (void *)(long)cpu;
unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
struct take_cpu_down_param tcd_param = {
.mod = mod,
.hcpu = hcpu,
};
if (num_online_cpus() == 1)
return -EBUSY;
if (!cpu_online(cpu))
return -EINVAL;
if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
return -ENOMEM;
cpu_hotplug_begin();
err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
hcpu, -1, &nr_calls);
if (err == NOTIFY_BAD) {
set_cpu_active(cpu, true);
nr_calls--;
__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
hcpu, nr_calls, NULL);
printk("%s: attempt to take down CPU %u failed\n",
__func__, cpu);
err = -EINVAL;
goto out_release;
}
/* Ensure that we are not runnable on dying cpu */
cpumask_copy(old_allowed, ¤t->cpus_allowed);
set_cpus_allowed_ptr(current, cpu_active_mask);
err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
if (err) {
set_cpu_active(cpu, true);
/* CPU didn't die: tell everyone. Can't complain. */
if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
hcpu) == NOTIFY_BAD)
BUG();
goto out_allowed;
}
BUG_ON(cpu_online(cpu));
/* Wait for it to sleep (leaving idle task). */
while (!idle_cpu(cpu))
yield();
/* This actually kills the CPU. */
__cpu_die(cpu);
/* CPU is completely dead: tell everyone. Too late to complain. */
if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
hcpu) == NOTIFY_BAD)
BUG();
check_for_tasks(cpu);
out_allowed:
set_cpus_allowed_ptr(current, old_allowed);
out_release:
cpu_hotplug_done();
if (!err) {
if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
hcpu) == NOTIFY_BAD)
BUG();
}
free_cpumask_var(old_allowed);
return err;
}
int __ref cpu_down(unsigned int cpu)
{
int err;
err = stop_machine_create();
if (err)
return err;
cpu_maps_update_begin();
if (cpu_hotplug_disabled) {
err = -EBUSY;
goto out;
}
set_cpu_active(cpu, false);
/*
* Make sure the all cpus did the reschedule and are not
* using stale version of the cpu_active_mask.
* This is not strictly necessary becuase stop_machine()
* that we run down the line already provides the required
* synchronization. But it's really a side effect and we do not
* want to depend on the innards of the stop_machine here.
*/
synchronize_sched();
err = _cpu_down(cpu, 0);
out:
cpu_maps_update_done();
stop_machine_destroy();
return err;
}
EXPORT_SYMBOL(cpu_down);
#endif /*CONFIG_HOTPLUG_CPU*/
/* Requires cpu_add_remove_lock to be held */
static int
|