waitqueue example works, kthread_uniterruptible completely wrong and renamed to schedule, params added

kernel_module/schedule.c

@@ -0,0 +1,58 @@
+/*
+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);
+}