QMutex::tryLock can lead to deadlocks when being called repeatedly. Attached is a file that will reproducible hang up sooner or later (or trigger "QMutex: mutex destroy failure: Device or resource busy" on exit). To reproduce compile and run it repeatedly:

g++ -I/usr/include/qt4/QtCore -I/usr/include/qt4/ /usr/lib64/libQtCore.so qmutex-trylock.cpp -o qmutex-trylock
while true; do ./qmutex-trylock; done

This was confirmed on multiple machines by multiple people, Thiago being one of them.

KDE Bug report: https://bugs.kde.org/show_bug.cgi?id=252659 (affects KDevelop 4.2)