c - 如何在 rmmod 上停止 Linux 内核线程？

Question

我写了下面的代码来创建一个内核线程:

#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);

在给出 insmod 命令时，我能够创建一个名为“pradeep”的内核线程，并且我可以使用ps -ef命令如下

root      6071     2  0 10:21 ?        00:00:00 [pradeep]

它的父线程是 kthreadd，它的 PID 是 2。但是我无法在发出 rmmod 命令时停止此线程。它给出以下输出:

ERROR: Removing 'pradeep': Device or resource busy.

有人可以告诉我如何终止这个线程吗？

Answer 1

您应该只使用kthread_create() 或kthread_run() 之一:

/**
 * 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;                                                               \
})

因此您正在创建两个 线程并泄漏其中一个:

task = kthread_create(&thread_function,(void*) &data,"pradeep");
task = kthread_run(&thread_function,(void*) &data,"pradeep");

此外，您的线程函数可能缺少一些细节:

/**
 * 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).
 */

我认为终止线程的两种选择是:

1. 完成后调用 do_exit()。
2. 当另一个线程调用kthread_stop()时返回一个值。

希望在解决这两个小问题后，您将拥有一个功能强大的线程创建器/收割器。