I think I'm seeing the same issue here on a Schenker XMG A506 notebook. The NV
GPU is the dedicated one. AFAIK all display hardware is connected to the Intel
iGPU.

Kernel is vanilla 4.6.1. Actually this is the first kernel (and the first time)
that I try to use the dedicated GPU.

lspci:
01:00.0 VGA compatible controller: NVIDIA Corporation GM107M [GeForce GTX 960M]
(rev a2)

Without runpm=0 even just calling DRI_PRIME=1 glxinfo leaves the system
unresponsive shortly afterwards. SysRq still works though.

Going to attach the part of the log in a second.