Dear Maintainer,

I'm stuck up when calling QOpenGLContext::create(), it didn't return, and one cpu
was totally occupied by QSGRenderThread, it looks like dead loop occurs in that
thread.

this's not always happening; and sometimes UI rendering error (like unexpected
chessboard-like pattern shows up in my GL render area) happens before this problem
occurs.

i'm using libGLX_mesa, and i'm not sure which side should responsible for this
problem, so i send this bugreport to you.

Regards,