At

https://github.com/openjdk/jdk/blob/dcac4b0a532f2ca6cb374da7ece331e8266ab351/src/hotspot/cpu/ppc/macroAssembler_ppc.cpp#L2742

ObjectMonitor::_succ is compared to null. Not equal means the unlock operation was successfully completed. This should be signaled by setting `flag` to EQ but instead it is NE at the end of the operation. Consequently the slow path will be taken to complete the monitor exit in the runtime.