Bugs in concurrent programs are extremely difficult to find and fix during testing. In this paper, we propose Kivati, which can efficiently detect and prevent atomicity violation bugs. Kivati imposes an average run-time overhead of 19%, which makes it practical to deploy on software in production environments. The key attribute that allows Kivati to impose this low overhead is its use of hardware watchpoints, which can be found on most commodity processors. Kivati combines watchpoints with a simple static analysis that annotates regions of codes that likely need to be executed atomically. The watchpoints are then used to monitor these regions for interleaving accesses that may lead to an atomicity violation. When an atomicity violation is detected, Kivati dynamically reorders the access to prevent the violation from occurring. Kivati can be run in prevention mode, which optimizes for performance, or in bug-finding mode, which trades some performance for an enhanced ability to find bugs.