Yeah plus Cc: stable for backporting and I think an igt or similar for panfrost to check this works correctly would be pretty good too. Since if it took us over 1 year to notice this bug it's pretty clear that normal testing doesn't catch this. So very likely we'll break this again.
Unfortunately there are a lot of kernel bugs which are noticed during actual use (but not CI runs), some of which have never been fixed. I do know the shrinker impl is buggy for us, if this is the fix I'm very happy.
btw for testing shrinkers recommended way is to have a debugfs file that just force-shrinks everything. That way you avoid all the trouble that tend to happen when you drive a system close to OOM on linux, and it's also much faster.
2nding this as a good idea.