how can i get the CPU number of current task (In kernel)?

Is there any way to get CPU number of current task?(What I need is not the number of CPUs the task is running on, but which CPU the task is running on)

This process must be in kernel-level, therefore something like command line won't help.

I am trying to do this by calling kernel functions or using kernel data structures(like task_struct), but I am having trouble.