it was introduced by this commmit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
which by itself is in a 4.12 vanilla code tree
which by itself is in a 4.12 vanilla code tree
https://github.com/torvalds/linux/commit/4c48abe91be03d191d0... (click the little '...' to expand tags it's in) or:
$ git tag --contains 4c48abe91be03d191d0c20cc755877da2cb35622
v4.13
What is your methodology that gets that it is in the 4.12 tree?