@sun @Starkimarm @tris @SuperDicq @toatrika @lxo Linux kernel is GPLv2 only. The code cannot be taken and used in an GPLv3 project. This is a very clear restriction on how the code can be used which is very often relevant. These kinds of license incompatibilities between licenses considered 'free' are a result of restrictions on how the code can be used. Some major projects exist due to these silly incompatibilities.
State enforced rules about how you can use the code is not freedom maximalism.