A collection drop and index creation on a primary node may interleave in a way that causes a two phase index build to start the index build on a drop-pending collection namespace (db.system.drop.*). This is partly due to the checks, introduced in SERVER-43403, that a collection drop has to bypass in SERVER-46122 when we have to potentially abort in-progress two phase index builds.

This bug affects configurations that disable majority reads or use the

storage engine.