It's not a, pardon me for the expression, fucking XNU specific programming rule - it is a general rule that was invented long before Ian got to it! You don't hold a reference counted pointer and operate on it without taking a :gasp: reference first - having that shit in your sample code is just, well extra shitty!

Also, separately from the dangling pointer issue, the first sentence of the post is literally - This post discusses a design issue at the core of the XNU kernel!