priority for kernel thread?

Hi,
In the code that I have written,I have 7 processes running.for two of the processes I have given real time priorities.In one of the work queue functions in my driver,I am handling real time data also.This is creating No queue(return value of my schedule_work call in driver)condition and is hanging the system.When I remove the real time priorities given to 2 user space processes,this problem gets solved.So my doubts are
1.Why a conflict arises between a kernel thread and user thread
2.Is there any way to give real time priority for a kernel thread(ie. a work queue function inside driver,similar to sched_setscheduler)

Thank You