A Synchronous IPC Protocol for Predictable Access to Shared Resources in Mixed-Criticality Systems

Abstract—In mixed-criticality systems, highly critical tasks must be temporally and logically isolated from faults in lower-criticality tasks. Such strict isolation, however, is difficult to ensure even for independent tasks, and has not yet been attained if low- and high-criticality tasks share resources subject to mutual exclusion constraints (e.g., shared data structures, peripheral I/O devices, or OS services), as it is often the case in practical systems. Taking a pragmatic, systems-oriented point of view, this pa-per argues that traditional real-time locking approaches are un-suitable in a mixed-criticality context: locking is a cooperative activity and requires trust, which is inherently in conflict with the paramount isolation requirements. Instead, a solution based on resource servers (in the microkernel sense) is proposed, and MC-IPC, a novel synchronous multiprocessor IPC protocol for invoking such servers, is presented. The MC-IPC protocol enables strict temporal and logical isola-tion among mutually untrusted tasks and thus can be used to share resources among tasks of different criticalities. It is shown to be practically viable with a prototype implementation in LITMUSRT and validated with a case study involving several antagonistic fail-ure modes. Finally, MC-IPC is shown to offer analytical benefits in the context of Vestal’s mixed-criticality task model. I