linux-kernel-module-cheat/kernel_module/schedule.c

/*
Let's block the entire kernel! Yay!

kthreads only allow interrupting if you call schedule.

If you don't, they just run forever, and you have to kill the VM.

Test with:

	dmesg -n 1
	insmod /schedule.ko yn=[01]
	dmesg | tail

Then:

- 	yn=0:
	- `qemu -smp 1`: everything blocks!
	- `qemu -smp 2`: you can still use the board, but is it noticeably slow
- 	yn=1: all good
*/

#include <linux/delay.h> /* usleep_range */
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <uapi/linux/stat.h> /* S_IRUSR | S_IWUSR */

MODULE_LICENSE("GPL");

static int yn = 1;
module_param(yn, int,  S_IRUSR | S_IWUSR);
MODULE_PARM_DESC(yn, "A short integer");

static struct task_struct *kthread;

static int work_func(void *data)
{
	unsigned int i = 0;
	while (!kthread_should_stop()) {
		pr_info("%u\n", i);
		i++;
		if (yn)
			schedule();
	}
	return 0;
}

int init_module(void)
{
	kthread = kthread_create(work_func, NULL, "mykthread");
	wake_up_process(kthread);
	return 0;
}

void cleanup_module(void)
{
	kthread_stop(kthread);
}