In kernel lots of objects are freed by rcu, in such cases free stack is close to useless, e.g.:
We should extend KASAN to be able to remember 1 or several aux stacks for each object in FIFO order, insert hooks that note aux stacks to call_rcu (and maybe timer/workqueue functions), and print aux stacks in reports.
Ideally, we don't increase alloc_info size for this. I think we need to get back to storing free_info inside of the object.