Some question about "security context of a task"

[loody]

hi Mulyadi:

2012/2/1 Mulyadi Santosa <mulyadi.santosa at gmail.com>:
> Hi....
>
> On Wed, Feb 1, 2012 at 14:12, loody <miloody at gmail.com> wrote:
>> below is the place it happen
>>
>> if (atomic_read(&p->real_cred->user->processes) >=
>>             p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
>
> Seems like a normal user limit checking...the one we usually set via
> "ulimit" command. Checking number of processes to be precise...
>
>> after checking the parameter, I found p->real_cred->user is NULL.
>
> hm, IMHO if it exceeds ulimit, the process creation should just stop.
Yes, I think you are right.

> Not sure why read_cred->user becomes NULL. Maybe that's for clean up,
> since later process will be terminated?

The "later process" you mean is the caller?
please let me describe my environment more detail.
1. when outside event happen
2. calling driver's probe.
3. I use kernel_thread to create a thread in probe function.
Then the sequence seems like:
kernel_thread
  -> do_fork
  -> copy_process
  ..........
  p = dup_task_struct(current);
  /*The user_struct user is inherited from current.*/
  ...........
if (atomic_read(&p->real_cred->user->processes) >=
             p->signal->rlim[RLIMIT_NPROC].rlim_cur) {
.......

Then it panic.
1. why kernel thread need user_struct
2. is it use for kernel thread to record how may user mode program it created?

Thanks for your help,