c - C Linux カーネル ページが以前の変数に干渉する

Question

readLinuxカーネルをフックして、ディレクトリ内のファイルを読み取るプロセスを表示したいと考えています/home/xytao/safe。

// get absolute file path from file struct
char *get_filename(struct file *file)
{
    char *buf = (char *)__get_free_page(GFP_KERNEL);
    if (!buf)
    {
        return NULL;
    }
    char *filename = dentry_path_raw(file->f_path.dentry, buf, PAGE_SIZE - 1);
    if (IS_ERR(filename))
    {
        free_page((unsigned long)buf);
        return NULL;
    }
    free_page((unsigned long)buf);
    return filename;
}

asmlinkage ssize_t fake_read(int __fd, void *__buf, size_t __nbytes)
{
    char *pathname;
    struct file *file;
    struct path *path;
    struct files_struct *files = current->files;
    spin_lock(&files->file_lock);
    file = fcheck_files(files, __fd);
    if (!file)
    {
        spin_unlock(&files->file_lock);
        return -ENOENT;
    }
    spin_unlock(&files->file_lock);
    ssize_t out = real_read(__fd, __buf, __nbytes);
    pathname=get_filename(file);
    if (!strncmp(pathname, "/home/xytao/safe", 15))
    {   fm_alert("pathname_before:%s\n", pathname);
        struct file *process_file = get_task_exe_file(current);
        fm_alert("process_name:%s\n", get_filename(process_file));
        fm_alert("pathname_after:%s\n:", pathname);    
    }
    return out;
}

しかしpathname、プロセス名を取得した後に変更されたようでpathname、get_filename(process_file).

たとえば、 を開いた後/home/xytao/safe/test、次の出力が得られます。

[ 1181.179485] fsmonko.fake_read: pathname_before:/home/xytao/safe/test
[ 1181.179488] fsmonko.fake_read: process_name:/usr/bin/gedit
[ 1181.179490] fsmonko.fake_read: pathname_after:/home/x/usr/bin/gedit
           :
[ 1181.181590] fsmonko.fake_read: pathname_before:/home/xytao/safe/test
[ 1181.181594] fsmonko.fake_read: process_name:/usr/bin/gedit
[ 1181.181595] fsmonko.fake_read: pathname_after:/home/x/usr/bin/gedit
           :
[ 1181.190503] fsmonko.fake_read: pathname_before:/home/xytao/safe/test
[ 1181.190509] fsmonko.fake_read: process_name:/usr/bin/gedit
[ 1181.190511] fsmonko.fake_read: pathname_after:/home/x/usr/bin/gedit
           :
[ 1197.523906] fsmonko.fake_read: pathname_before:/home/xytao/safe/test
[ 1197.523915] fsmonko.fake_read: process_name:/usr/bin/nautilus

これを修正する方法は？