The error message "QEventDispatcherUNIX: internal error, wakeUps.testAndSetRelease(1, 0) failed!" is constantly being written to the error logs, which was filling up our disk and using 100% of one CPU.

The call in qt/src/corelib/kernel/qeventdispatcher_unix.cpp:
(!wakeUps.testAndSetRelease(1, 0)) {

should never fail. The issue might be derived from here qt/src/corelib/arch/qatomic_sparc.h:
inline bool QBasicAtomicInt::testAndSetOrdered(int expectedValue, int newValue)

It will return false if the value it is set currently is not the expected one. So, either the setting of it is failing of q_atomic_lock_int is.