[Mesa-dev] Crash inside iris_dri.so when using the OpenGL backend in Cairo on Ubuntu 20.04

[Filip Strömbäck]

Dear mesa-dev,

I recently updated my system, and it seems like Mesa is now using the 
new iris driver for my Intel GPU (a Lenovo Thinkpad), which makes a 
program I'm developing crash somewhere inside iris_dri.so (it is drawing 
using the GLX backend in Cairo). Forcing the old i965 driver with the 
environment variable solves the problem, which makes me suspect a bug 
(or at least more strict behavior) in the new iris driver compared to 
the old one.

Is this a known issue, or should I report it as a bug? It might as well 
be the case that Cairo is misbehaving subtly, but that the behavior was 
tolerated by the old i965 driver.

My short-term solution (which is perhaps better anyway) is to migrate 
away from the experimental GL backend in Cairo, but as this could 
indicate a bug in the iris driver I thought it might be interesting for 
you to be aware of.

The program is available in compiled form here: 
https://www.ida.liu.se/~TDDI16/2020/tutorials/trees.tar (I might update 
it during the coming days to work around the bug). I can provide both 
source and compiled binaries that reproduce the problem more 
consistently if you wish to investigate further. The linked program 
requires some interaction to crash, but crashes fairly consistently.

With kind regards,
Filip Strömbäck