From a performance point of view, this doesn't matter. Incomplete split are extremely rare. For convenience, though, I added a new function specifically for handling these "leftover" incomplete splits as opposed to finishing a split that you just made, which performs the lock-upgrade. See attached. I think that helps with readability, and makes it less likely that we'll forget the lock-upgrade in the future if the insertion code is refactored.
I think that the lock-upgrade in the ginFinishOldSplit function is unsafe
because it violates the requirement of the ginStepRight function that
"The next page is locked first, before releasing the current page.”
