Priority inversion comes about when a low-priority task holds a resource
that is needed by a higher-priority task, with the result that the wrong
task is the only one that can run. This problem is arguably most acute in
realtime settings, but it can happen in just about any system that has
multiple tasks running. The variety of
scheduling classes provided by the Linux kernel make handling priority
inversion a difficult problem; the latest version of the proxy
execution patch series points toward a possible solution.

Source: LWN.net – [$] Addressing priority inversion with proxy execution