"SystemTap was given as an example here: according to Linus, time has shown that the SystemTap interface is not a good one."
What mush. systemtap was never proposed for pulling. In any case, systemtap does not provide a kernel interface or ABI. Perhaps he meant "utrace", but that also was not a user-space ABI. So I can't see what he might have meant in this context. Can someone clarify / correct?