There are tools that get used by maintainers. For example, patchwork is used by many subsystem trees to track patches and the discussion around them. And th

There are tools that get used by maintainers. For example, patchwork is used by many subsystem trees to track patches and the discussion around them. And those developers and maintainers who fix bugs (and who are getting paid for it, as opposed to bugs that get fixed for free), do generally use some bug tracking system, but it tends to be one specific for the production kernel tree or product tree. Yes, that means that there is some duplication of effort, but the fact of the matter is that people don't use the upstream kernel tree directly for any product or production service, so having a bugzilla tree for that only makes sense if you have a large team of people who are exclusively working on upstream --- and often times, that's not the case.