Data races are a major contributor to parallel software unreliability. A type of race that is both common and typically harmful is the Asymmetric data race. It occurs when at least one of the racing threads is inside a critical section. Current proposals that target them are software-based. They slow down execution and require significant compiler, operating system (OS), or application changes. This paper proposes the first scheme to tolerate asymmetric data races in production runs with negligible execution overhead. The scheme, called Pacman, exploits cache coherence hardware to temporarily protect the variables that a thread accesses in a critical section from other threads' requests. Unlike previous schemes, Pacman induces negligible slowdown, needs no support from the compiler or (in the baseline design) from the OS, and requires no application source code changes. In addition, its hardware is relatively unintrusive. We test Pacman with the SPLASH-2, PARSEC, Sphinx 3, and Apache codes, and discover two unreported asymmetric data races.

A particularly insidious type of concurrency bug is atomicity violations. While there has been substantial work on automatic detection of atomicity violations, each existing technique has focused on a certain type of atomic region. To address this limitation, this paper presents Atom Tracker, a comprehensive approach to atomic region inference and violation detection. Atom Tracker is the first scheme to (1) automatically infer generic atomic regions (not limited by issues such as the number of variables accessed, the number of instructions included, or the type of code construct the region is embedded in) and (2) automatically detect violations of them at runtime with negligible execution overhead. Atom Tracker provides novel algorithms to infer generic atomic regions and to detect atomicity violations of them. Moreover, we present a hardware implementation of the violation detection algorithm that leverages cache coherence state transitions in a multiprocessor. In our evaluation, we take eight atomicity violation bugs from real-world codes like Apache, MySql, and Mozilla, and show that Atom Tracker detects them all. In addition, Atom Tracker automatically infers all of the atomic regions in a set of micro benchmarks accurately. Finally, we also show that the hardware implementation induces a negligible execution time overhead of 0.2-4.0% and, therefore, enables Atom Tracker to find atomicity violations on-the-fly in production runs.