Formal Verification of Resource Synchronization Protocol Implementations: A Case Study in RTEMS

Abstract

To avoid race conditions and ensure data integrity, resource synchronization protocols have been widely studied in real-time systems for decades, providing systematical policies to guarantee a bound on priority inversion-induced blocking time and the avoidance of deadlocks. However, the corresponding realization is often based on assumed abstractions and necessary adaptions in a real-time operating system, by which the theoretically proven properties of such a protocol may not be delivered, leading to potential mismatches. To prevent such mismatches, in this work, we propose to contract the obligations of involved primitives and operations, and apply the deductive verification on a corresponding implementation. To this end, we present a modularized verification framework and demonstrate its applicability by verifying the official implementation of the immediate ceiling priority protocol (ICPP) and the multiprocessor resource sharing protocol (MrsP) in RTEMS, resulting in the discovery of long-stayed mismatches for both synchronization protocols. To resolve them, we provide a possible remedy for the ICPP and an additional precondition regarding nested locking for the MrsP.