Hey folks, since kernel 4.6.2 I got a lot of X11 freezes as well as unusable gui tools (delayed inputs, scrolling and broken display rendering). Also all the virtual box clients are behaving the same. Only the chromium gui and xterm were usable (well, xterm only on my host, not on the virtual box clients).
I tried my best and here are the changes I made that stopped the system from a total freeze since four days:
run as root
cat /etc/X11/xorg.conf.d/20-intel-graphics.conf < DELIM Section "Device" Identifier "Intel Graphics" Driver "intel" Option "AccelMethod" "uxa" Option "NoAccel" "True" EndSection DELIM
I am crossing fingers it is working on your machine also.