...
To trigger the reassignment cancellation, a new znode /admin/cancel_reassignment_in_progress is created, the controller will be informed of the reassignment cancellation via a ZooKeeper watch on this. The controller will read the current pending reassignments in /admin/reassign_partitions and re-populate ControllerContext.partitionReplicaAssignmentpartitionsBeingReassigned. For each pending topic/partition reassignments, the cancellation /rollback works like below, it's like the opposite of doing reassignments, since we have the "original_replicas" of each topic/partition reassignments in /admin/reassign_partitions & ControllerContext.partitionReplicaAssignmentpartitionBeingReassigned, it is much easier to rollback.
...