Simple Linux kernel module to toggle running process state between "D" (uninterruptible) and interruptible

README.md

This is related to:

• Creating controllable D state (uninterruptible sleep) processes

Makefile

ccflags-y := -DDEBUG -Wfatal-errors

ifneq ($(KERNELRELEASE),)
	obj-m += state-toggle.o
else
	BUILD_KERNEL ?= /lib/modules/$(shell uname -r)/build
default:
	$(MAKE) -C $(BUILD_KERNEL) M=$(CURDIR) modules
endif

all: default

clean:
	$(MAKE) -C $(BUILD_KERNEL) M=$(CURDIR) clean

install: default
	$(MAKE) -C $(BUILD_KERNEL) M=$(CURDIR) modules_install

state-toggle.c

#define DEFAULT_NAME "state-toggle"
#define KMSG_COMPONENT DEFAULT_NAME
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>

MODULE_AUTHOR("");
MODULE_DESCRIPTION("");
MODULE_VERSION("0.1.0");
MODULE_LICENSE("GPL");

static struct kobject *toggle_kobj;

static ssize_t pid_store(struct kobject *kobj, struct kobj_attribute *attr,
			 const char *buf, size_t count)
{
	pid_t pid;
	struct task_struct *task;
	int old_state, state;

	if (count >= PAGE_SIZE)
		return -EINVAL;

	if (kstrtoint(buf, 0, &pid) < 0)
		return -EINVAL;

	task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
	if (!task)
		return -ENOENT;

	old_state = task->__state;

	state = TASK_UNINTERRUPTIBLE;
	if (old_state & TASK_UNINTERRUPTIBLE)
		state = TASK_INTERRUPTIBLE;

	task->__state = state; /* This is generally a no-no. */

	pr_info("%s(%d): %c (0x%02x) -> %c (0x%02x)\n", task->comm, task->pid,
		task_index_to_char(old_state), old_state, task_index_to_char(state),
		state);

	/* Wake the task up so it can consume any pending signals. */
	if (state & TASK_INTERRUPTIBLE)
		wake_up_process(task);

	return count;
}

static struct kobj_attribute pid_attr = __ATTR_WO(pid);

static struct attribute *toggle_attrs[] = {
	&pid_attr.attr,
	NULL,
};

static struct attribute_group toggle_group = {
	.attrs = toggle_attrs,
};

static int __init toggle_init(void)
{
	int ret;

	/* Add an entry under /sys/kernel as /sys/kernel/state-toggle/pid. */
	toggle_kobj = kobject_create_and_add(DEFAULT_NAME, kernel_kobj);
	if (IS_ERR(toggle_kobj))
		return -ENOMEM;

	ret = sysfs_create_group(toggle_kobj, &toggle_group);
	if (ret)
		goto error;

	return 0;

error:
	kobject_put(toggle_kobj);
	return -ENOSYS;
}

static void __exit toggle_exit(void)
{
	kobject_put(toggle_kobj);
}

module_init(toggle_init);
module_exit(toggle_exit);