quoted

From some light research, I can't find a trace of RCU sync. Pity, I'll
need to move furhter investigation to later. I'll report back if I have
something, but it may take a while. Thanks for the help!

If you don't want to spend too much time you can just call it yourself
right? :) Put a synchronize_rcu() with a comment about concurrent stat
reading after pdata->is_open = false; and that's it?

Probably. Although I trust you, I would still add code which I a) don't
fully understand myself yet and b) feels somehow wrong because something
like synchronize_rcu() should likely not be in drivers but somewhere
more generic. Given that the bug in this driver went unnoticed for years
(same with the race in other drivers), I do prefer to come back later
with the good feeling that I understood the problem and fixed it
thoroughly.