Revert "kthread.c - Removing conflicted stuffs"

This reverts commit 99970e8d8ae06f6f9b6519af27a0926892e452ce.
Revert "kthread: Prevent unpark race which puts threads on the wrong cpu"

This reverts commit 3c4d1d64ec2aacdfdf611693ea4c3f3db4098604.