Puzzle on Priority Ceiling Protocol

[CARERI/SED]

I am confused with the Priority Ceiling Protocol implemented in the rtems.

I learn that the protocol defined as "The priority ceiling of a semaphore is defined as the priority of the highest priority task that may lock this semaphore. A task T is allowed to enter a critical section only if its assigned priority is higher than the priority ceilings of all semaphores currently locked by tasks other than T."
But RTEMS doesn't seem to conform to it when I leafed through the code in coremutex.c.

I am not sure what principle RTEMS uses as to Priority Ceiling Protocol.
Would you mind explaining it or pointing out where I can get help ?
Thanks a lot in advance.