How to stop Linux kernel threads on rmmod?

Question

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?

Answer 1

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:

1. Call do_exit() when you're done.
2. Return a value when another thread calls kthread_stop().

Hopefully after fixing these two small problems, you'll have a functional thread creator / reaper.

Answer 2

I hope the below program resolves your problem.... thumbs up :-)

`#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;      printk(KERN_INFO "IN THREAD FUNCTION");      while(!kthread_should_stop()){              schedule();              }      /*do_exit(1);*/   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) {    kthread_stop(task); }  module_init(kernel_init); module_exit(kernel_exit); MODULE_AUTHOR("SHRQ"); MODULE_LICENSE("GPL");