searchMethodInner iterates up the inheritance hierarchy and calls searchMethodCommon on each module in the chain, but searchMethodCommon also calls searchMethodInner on its superClass! This results in ridiculous exponential expansion of work when a method can't be found. To reproduce the issue:

cls = Class.new
20.times { cls = Class.new(cls) }
cls.non_existing_method rescue nil

Calling non_existing_method takes ~8 sec at a depth of 20, ~14 sec at 21, ~26 sec at 22, etc.

I'm not quite sure what the right fix is, since this is in prepend territory, but it's a definite problem right now.