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/* https://cirosantilli.com/linux-kernel-module-cheat#wait-queues */

#include <linux/delay.h> /* usleep_range */

#include <linux/kernel.h>

#include <linux/kthread.h>

#include <linux/module.h>

#include <linux/wait.h> /* wait_queue_head_t, wait_event_interruptible, wake_up_interruptible */

static struct task_struct *kthread_wake;

static struct task_struct *kthread_sleep1;

static struct task_struct *kthread_sleep2;

static wait_queue_head_t queue;

static atomic_t awake1 = ATOMIC_INIT(0);

static atomic_t awake2 = ATOMIC_INIT(0);

static int kthread_wake_func(void *data)

{

unsigned int i = 0;

while (!kthread_should_stop()) {

pr_info("0 %u\n", i);

usleep_range(1000000, 1000001);

atomic_set(&awake1, 1);

atomic_set(&awake2, 1);

wake_up(&queue);

i++;

}

return 0;

}

static int kthread_sleep_func_1(void *data)

{

unsigned int i = 0;

while (!kthread_should_stop()) {

pr_info("1 %u\n", i);

i++;

wait_event(queue, atomic_read(&awake1));

atomic_set(&awake1, 0);

schedule();

}

return 0;

}

static int kthread_sleep_func_2(void *data)

{

unsigned int i = 0;

while (!kthread_should_stop()) {

pr_info("2 %u\n", i);

i++;

wait_event(queue, atomic_read(&awake2));

atomic_set(&awake2, 0);

schedule();

}

return 0;

}

int init_module(void)

{

init_waitqueue_head(&queue);

kthread_wake = kthread_create(kthread_wake_func, NULL, "wake");

kthread_sleep1 = kthread_create(kthread_sleep_func_1, NULL, "sleep1");

kthread_sleep2 = kthread_create(kthread_sleep_func_2, NULL, "sleep2");

wake_up_process(kthread_wake);

wake_up_process(kthread_sleep1);

wake_up_process(kthread_sleep2);

return 0;

}

void cleanup_module(void)

{

kthread_stop(kthread_sleep2);

kthread_stop(kthread_sleep1);

kthread_stop(kthread_wake);

}

MODULE_LICENSE("GPL");