Sharing an exclusive-use resource (R in this case) in a well-designed system typically involves L relinquishing R promptly so that H (a higher-priority task) does not stay blocked for excessive periods of time.
The trouble experienced by the Mars Pathfinder lander in 1997[1][2] is a classic example of problems caused by priority inversion in realtime systems.
Low-priority tasks usually have a low priority because it is not important for them to finish promptly (for example, they might be a batch job or another non-interactive activity).
Because priority inversion results in the execution of a lower-priority task blocking the high-priority task, it can lead to reduced system responsiveness or even the violation of response time guarantees.
Lampson and Redell[3] published one of the first papers to point out the priority inversion problem.