This is what I am trying to do in linux kernel. When some event occurs; Process X wants to tell process Y to un-schedule itself(Y) [ and change state from "running or ready to run" to "not ready to run until told otherwise" ]. Process X will take care of waking up Y later.

One approach probably is to set "need_resched" for process Y so that schedular picks another process at the first opportunity. Is there any other alternative ? Is it safe to do this from interrupt context instead of process X's context ?

Sunil