Verification of a Lock-Free Implementation of Multiword LL/SC Object

On shared memory multiprocessors, synchronization often turns out to be a performance bottleneck and the source of poor fault-tolerance. By avoiding locks, the significant benefit of lock (or wait)-freedom for real-time systems is that the potentials for deadlock and priority inversion are avoided. The lock-free algorithms often require the use of special atomic processor primitives such as CAS (Compare And Swap) or LL/SC (Load Linked/Store Conditional). However, many machine architectures support either CAS or LL/SC, but not both. In this paper, we present a lock-free implementation of the ideal semantics of LL/SC using only pointer-size CAS, and show how to use refinement mapping to prove the correctness of the algorithm.