I wrote the following code to create a kernel thread:
#include<linux/init.h>
#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/kthread.h>
#include<linux/sched.h>
struct task_struct *task;
int data;
int ret;
int thread_function(void *data)
{
int var;
var = 10;
return var;
}
static int kernel_init(void)
{
data = 20;
printk(KERN_INFO"--------------------------------------------");
task = kthread_create(&thread_function,(void *)data,"pradeep");
task = kthread_run(&thread_function,(void *)data,"pradeep");
printk(KERN_INFO"Kernel Thread : %s\n",task->comm);
return 0;
}
static void kernel_exit(void)
{
ret = kthread_stop(task);
}
module_init(kernel_init);
module_exit(kernel_exit);
On giving the insmod command, I am able to create a kernel thread named "pradeep" and I can see the new thread using the
ps -ef
command as follows
root 6071 2 0 10:21 ? 00:00:00 [pradeep]
and its parent is kthreadd whose PID is 2.
But I am not able to stop this thread on giving rmmod
command. It is giving the following output:
ERROR: Removing 'pradeep': Device or resource busy.
Can somebody please tell me how to kill this thread?
You should use only one of kthread_create()
or kthread_run()
:
/**
* kthread_run - create and wake a thread.
* @threadfn: the function to run until signal_pending(current).
* @data: data ptr for @threadfn.
* @namefmt: printf-style name for the thread.
*
* Description: Convenient wrapper for kthread_create() followed by
* wake_up_process(). Returns the kthread or ERR_PTR(-ENOMEM).
*/
#define kthread_run(threadfn, data, namefmt, ...) \
({ \
struct task_struct *__k \
= kthread_create(threadfn, data, namefmt, ## __VA_ARGS__); \
if (!IS_ERR(__k)) \
wake_up_process(__k); \
__k; \
})
So you're creating two threads and leaking one of them:
task = kthread_create(&thread_function,(void*) &data,"pradeep");
task = kthread_run(&thread_function,(void*) &data,"pradeep");
Furthermore, your thread function might be missing some details:
/**
* kthread_create - create a kthread.
* @threadfn: the function to run until signal_pending(current).
* @data: data ptr for @threadfn.
* @namefmt: printf-style name for the thread.
*
* Description: This helper function creates and names a kernel
* thread. The thread will be stopped: use wake_up_process() to start
* it. See also kthread_run().
*
* When woken, the thread will run @threadfn() with @data as its
* argument. @threadfn() can either call do_exit() directly if it is a
* standalone thread for which noone will call kthread_stop(), or
* return when 'kthread_should_stop()' is true (which means
* kthread_stop() has been called). The return value should be zero
* or a negative error number; it will be passed to kthread_stop().
*
* Returns a task_struct or ERR_PTR(-ENOMEM).
*/
I think the two choices for terminating a thread are:
do_exit()
when you're done.kthread_stop()
.Hopefully after fixing these two small problems, you'll have a functional thread creator / reaper.