Note the replies-to-self from Linus, like https://lore.kernel.org/all/CAHk-=whaiVhuO7W1tb8Yb-CuUHWn7bBnJ3bM7bvcQiEQwv_WrQ@mail.gmail.com/t/#u

""""Oh, and the fact that it hasn't been in linux-next became immediately clear, and it's a real practical problem.

I get a compile error when just doing a basic built-test: […] 

and that compile error is actually a sign of a pretty serious bug.

BTREE_NODE_UNLOCKED is of the wrong enum type, and has a value (-1) that simply cannot be represented in a 'enum six_lock_type'."""