Weird interaction between QT and Nvidia proprietary driver for linux makes it impossible to close the Konsole

KDE Plasma 5 Konsole application has become unusable on linux systems with NVIDIA graphics and the NVIDIA proprietary driver (maybe restricted to the NVIDIA 340 and NVIDIA 361 driver series).

When one tries to close the Konsole, a process is left behind, using 100% cpu.

The bug seems to appear with some versions of the NVIDIA drivers (e.g. < 361.18) and disappear for others (361.18) and reappear again (361.28), with some suspicion that nvidia never touched anything relevant to the issue and that the different driver versions merely slightly change the timing of things, so that a race may end fine in one case and with an issue in another.

To the kde developers, the Konsole code is fine (it is not their bug), to the bug must be in something behind the Konsole code.

See also https://bugs.kde.org/show_bug.cgi?id=343803

People from NVIDIA also say that it is not their fault

"From what I've seen it may not be the nVidia driver which is at fault. There seems to be a complicated threading issue which might or might not be caused by the driver...it may just be this driver exposes the issue differently."

See also https://devtalk.nvidia.com/default/topic/879586/linux/kf5-konsole-15-04-and-15-08-consumes-100-cpu-on-close-only-with-proprietary-nvidia-driver/

Hard to say if this is a bug in the NVIDIA proprietary drivers or QT triggering a race somewhere. However, even if it is a NVIDIA problem, helping identify it (to properly report to NVIDIA) or working around it could be important.