[PATCH 5/7] pid: rewrite task helper function is_global_init() avoiding task->pid

[Oleg Nesterov]

On 01/23, Richard Guy Briggs wrote:
>
>  static inline int is_global_init(struct task_struct *tsk)
>  {
> -	return tsk->pid == 1;
> +	return task_pid_nr(tsk) == 1;
>  }

ACK, but we need to fix it.

With or without this change is_global_init() actually means
is-the-main-thread-of-global-init.

This is not what the callers actually want. Just look at
oom_unkillable_task(). Suppose that p is the sub-thread of
/sbin/init, if we kill this thread we kill the whole process.

The same of other callers. is_global_init() should return T
if this task is the part of init's thread group.

Oleg.