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/* Copyright 2008, 2005 Rusty Russell rusty@rustcorp.com.au IBM Corporation.
* GPL v2 and any later version.
*/
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/stop_machine.h>
#include <linux/syscalls.h>
#include <linux/interrupt.h>
#include <asm/atomic.h>
#include <asm/uaccess.h>
/* This controls the threads on each CPU. */
enum stopmachine_state {
/* Dummy starting state for thread. */
STOPMACHINE_NONE,
/* Awaiting everyone to be scheduled. */
STOPMACHINE_PREPARE,
/* Disable interrupts. */
STOPMACHINE_DISABLE_IRQ,
/* Run the function */
STOPMACHINE_RUN,
/* Exit */
STOPMACHINE_EXIT,
};
static enum stopmachine_state state;
struct stop_machine_data {
int (*fn)(void *);
void *data;
int fnret;
};
/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
static unsigned int num_threads;
static atomic_t thread_ack;
static struct completion finished;
static DEFINE_MUTEX(lock);
static void set_state(enum stopmachine_state newstate)
{
/* Reset ack counter. */
atomic_set(&thread_ack, num_threads);
smp_wmb();
state = newstate;
}
/* Last one to ack a state moves to the next state. */
static void ack_state(void)
{
if (atomic_dec_and_test(&thread_ack)) {
/* If we're the last one to ack the EXIT, we're finished. */
if (state == STOPMACHINE_EXIT)
complete(&finished);
else
set_state(state + 1);
}
}
/* This is the actual thread which stops the CPU. It exits by itself rather
* than waiting for kthread_stop(), because it's easier for hotplug CPU. */
static int stop_cpu(struct stop_machine_data *smdata)
{
enum stopmachine_state curstate = STOPMACHINE_NONE;
/* Simple state machine */
do {
/* Chill out and ensure we re-read stopmachine_state. */
cpu_relax();
if (state != curstate) {
curstate = state;
switch (curstate) {
case STOPMACHINE_DISABLE_IRQ:
local_irq_disable();
hard_irq_disable();
break;
case STOPMACHINE_RUN:
/* |= allows error detection if functions on
* multiple CPUs. */
smdata->fnret |= smdata->fn(smdata->data);
break;
default:
break;
}
ack_state();
}
} while (curstate != STOPMACHINE_EXIT);
local_irq_enable();
do_exit(0);
}
/* Callback for CPUs which aren't supposed to do anything. */
static int chill(void *unused)
{
return 0;
}
int __stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
{
int i, err;
struct stop_machine_data active, idle;
struct task_struct **threads;
active.fn = fn;
active.data = data;
active.fnret = 0;
idle.fn = chill;
idle.data = NULL;
/* This could be too big for stack on large machines. */
threads = kcalloc(NR_CPUS, sizeof(threads[0]), GFP_KERNEL);
if (!threads)
return -ENOMEM;
/* Set up initial state. */
mutex_lock(&lock);
init_completion(&finished);
num_threads = num_online_cpus();
set_state(STOPMACHINE_PREPARE);
for_each_online_cpu(i) {
struct stop_machine_data *smdata = &idle;
struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
if (!cpus) {
if (i == first_cpu(cpu_online_map))
smdata = &active;
} else {
if (cpu_isset(i, *cpus))
smdata = &active;
}
threads[i] = kthread_create((void *)stop_cpu, smdata, "kstop%u",
i);
if (IS_ERR(threads[i])) {
err = PTR_ERR(threads[i]);
threads[i] = NULL;
goto kill_threads;
}
/* Place it onto correct cpu. */
kthread_bind(threads[i], i);
/* Make it highest prio. */
if (sched_setscheduler_nocheck(threads[i], SCHED_FIFO, ¶m))
BUG();
}
/* We've created all the threads. Wake them all: hold this CPU so one
* doesn't hit this CPU until we're ready. */
get_cpu();
for_each_online_cpu(i)
wake_up_process(threads[i]);
/* This will release the thread on our CPU. */
put_cpu();
wait_for_completion(&finished);
mutex_unlock(&lock);
kfree(threads);
return active.fnret;
kill_threads:
for_each_online_cpu(i)
if (threads[i])
kthread_stop(threads[i]);
mutex_unlock(&lock);
kfree(threads);
return err;
}
int stop_machine(int (*fn)(void *), void *data, const cpumask_t *cpus)
{
int ret;
/* No CPUs can come up or down during this. */
get_online_cpus();
ret = __stop_machine(fn, data, cpus);
put_online_cpus();
return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);
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