A method, system, and computer usable program product for using a dual mode reader writer lock. A contention condition is detected in the use of a lock in a data processing system, the lock being used for managing read and write access to a resource in the data processing system. A determination of the data structure used for implementing the lock is made. If the data structure is a data structure of a reader writer lock (RWL), the data structure is transitioned to a second data structure suitable for implementing the DML. A determination is made whether the DML has been expanded. If the DML is not expanded, the DML is expanded such that the data structure includes an original lock and a set of expanded locks. The original lock and each expanded lock in the set of expanded locks forms an element of the DML.