Felix Tomski

Remote Memory Access (RMA) programming models enable processes running on a distributed-memory computer to access and manipulate the memory of other processes directly. Such one-sided communication has the benefit that the receiving process is not actively involved in the communication compared to the classical two-sided message-passing model. The three programming models MPI RMA, OpenSHMEM, and GASPI provide such a communication scheme. However, RMA models require the developer to synchronize the accesses with corresponding API calls correctly. Concurrent modifications of the same (remote) memory location due to wrong or missing synchronization lead to data races. Such data races are undefined behavior and may result in non-deterministic failures of the program execution. This paper presents RMASanitizer, an on-the-fly race detector for MPI RMA, OpenSHMEM, and GASPI applications. It relies on a generalized race detection model independent of the concrete RMA programming model. RMASanitizer combines a dynamic on-the-fly analysis with a static analysis at compile-time that detects and instruments only relevant memory accesses. It is implemented as part of the MPI correctness checking framework MUST which we extended with support for OpenSHMEM and GASPI. We show that RMASanitizer can detect races in MPI RMA, OpenSHMEM, and GASPI applications with an accuracy of over 95 percent by running it on the data race benchmark suite RMARaceBench. On proxy applications, the slowdown for the execution with up to 700 processes ranges from 1.1x to 30x, depending on the application, showing that our tool is applicable in practice.