Priority inversion occurs when a higher priority process is blocked by one or more lower priority processes for a long time. The use of synchronization primitives such as mutual-exclusion locks in the SunOS 5.0 through 5.8 kernel can lead to priority inversion.
The problem of priority inversion has been addressed for mutual-exclusion locks for the SunOS 5.0 through 5.8 kernel by implementing a basic priority inheritance policy. The policy states that a lower priority process inherits the priority of a higher priority process when the lower priority process blocks the execution of the higher priority process. This places an upper bound on the amount of time a process can remain blocked. The policy is a property of the kernel's behavior, not a solution that a programmer institutes through system calls or function execution. User-level processes can still exhibit priority inversion, however.