CCSK is a reversible form of CCS which is causal, meaning that ac-
tions can be reversed if and only if each action caused by them has already been
reversed; there is no control on whether or when a computation reverses. We pro-
pose an event structure semantics for CCSK. For this purpose we define a cat-
egory of reversible bundle event structures, and use the causal subcategory to
model CCSK. We then modify CCSK to control the reversibility with a rollback
primitive, which reverses a specific action and all actions caused by it. To define
the event structure semantics of rollback, we change our reversible bundle event
structures by making the conflict relation asymmetric rather than symmetric, and
we exploit their capacity for non-causal reversibility.