The following sequence of events can cause an overcommit
--> Launch task is called for a task whose executor is already running
--> Executor's resources are not accounted for on the master
--> Executor exits and the event is enqueued behind launch tasks on the master
--> Master sends the task to the slave which needs to commit for resources for task and the (new) executor.
--> Master processes the executor exited event and re-offers the executor's resources causing an overcommit of resources.