Get full process path from pid in kernel linux

I'm building custom kernel linux for my device (like embeded device). I want to log all information of kill system call. So I modify code in kill system call and get pid to kill. But I can't get full process path for it, I have just get full path of current process. This is my code to get process path from pid.

long GetProcessPathFromPid(const pid_t p_id, char* pszProcessPath, int iSize)
{
    struct task_struct *task = NULL;
    struct pid *pid_struct = NULL;
    struct mm_struct *mm = NULL;
    //struct file *exe_file = NULL;
    //char buf[256] = {0};
    //char *result = ERR_PTR(-ENOENT);
    //int iResultLength = 0;

    pid_struct = find_get_pid(p_id);
    if (pid_struct == NULL)
    {
        printk("Fail to find_get_pid.\n");
    }
    task = pid_task(pid_struct, PIDTYPE_PID);                               // Get task_struct
    if (task == NULL) 
    {
        printk("Fail to pid_task.\n");
    }
    mm = get_task_mm(task);                                                // Get mm of task_struct
    mmput(mm);

    printk("Finish hook kill process\n.");
    return 0;                                              // Get mm of task_struct
}

And this is error when I update firmware:

Call Trace:
[<8042971c>] printk+0x24/0x30
[<800c37c8>] GetProcessPathFromPid+0x38/0x88
[<800c3b60>] LogKillProcess+0x64/0xf4
[<800443d4>] sys_kill+0x30/0x1d8
[<800354b0>] do_wait+0x11c/0x220
[<8042e234>] wait_for_completion_killable+0x18/0x30
[<80043a3c>] set_current_blocked+0x30/0x48
[<80533210>] repair_env_string+0x0/0x94
[<8003664c>] sys_wait4+0x80/0xfc
[<800344d8>] child_wait_callback+0x0/0x8c
[<80533210>] repair_env_string+0x0/0x94
[<8001b59c>] stack_done+0x20/0x40
[<800b07a8>] sys_close+0x0/0x158
[<80533210>] repair_env_string+0x0/0x94


Call Trace:
[<8042fe88>] _raw_spin_lock+0x10/0x3c
[<8002ef68>] get_task_mm+0x20/0x7c
[<800c37c8>] GetProcessPathFromPid+0x38/0x88
[<800c3b60>] LogKillProcess+0x64/0xf4
[<800443d4>] sys_kill+0x30/0x1d8
[<8001b59c>] stack_done+0x20/0x40


Code: 24630001  af830014  3c020001 <c0830000> 00622821  e0850000  10a0fffc  00032c02  3063ffff 
pe=GPON

---[ end trace aee100dae37dfc66 ]---
note: init[1] exited with preempt_count 1
FinWLmngr Daeish hook kill process
.mon is running
 !!!!   PLL locked !!!!!!     !!!!   RX CDR locked !!!!!!     !!!!   TX CDR locked !!!!!!    GPON BEN Calibration Done 
GPON SerDes Initialization Sequence Done 
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Can you help me? Thanks!

I found way to get full path process from pid. Full path process is symlink of /proc//exe, so I must find symlink of it. Here is code:

long GetSymLinkOfFile(const char *pzsFilePath, char *pszRealPath, int iSize)
{
    struct path path_struct;
    char pszBuffer[256];
    char *result = ERR_PTR(-ENOENT);
    int err = 0;
    int iLengthOfResult = 0;

    if (pzsFilePath == NULL || pszRealPath == NULL)
    {
        printk("Buffer is NULL.\n");
        return -EINVAL;
    }

    err = kern_path(pzsFilePath, LOOKUP_FOLLOW, &path_struct);

    if (err < 0)
    {
        printk("kern_path error, error code: %d", err);
        return iLengthOfResult;
    }

    result = d_path(&path_struct, pszBuffer, 256);

    if (IS_ERR(result) == true)
    {
        printk("d_path GetSymlink error: %s", result);
        return iLengthOfResult;
    }

    iLengthOfResult = strlen(result);

    if (iLengthOfResult <= iSize)
        strcpy(pszRealPath, result);

    return iLengthOfResult;
}