Comment # 1 on bug 106324 from Darek

This [1] patch prevents random xserver freezes
tested:
GPU GTX 550Ti
mesa 18.1.0rc2
xorg-server 1.19.99.905
xf86-video-nouveau-git 1.0.15.r5.gac8f7b9
DRI3 enabled

I noted the same behavior with:
mesa 18.0.1-1
xorg-server 1.19.6+13+gd0d1a694f-2
xf86-video-nouveau-git 1.0.15.r5.gac8f7b9
DRI3 enabled

[1] https://patchwork.freedesktop.org/series/41258/ (rev 4)

I'm not sure if it is related, but it's worth mentioning