I think Russia's view would be rational if there wasn't a history of North Korea progressing for decades towards a competent nuclear weapons capability and their practice of sharing that technology with Iran and other trouble makers.
What Russia and/or China could do is sign a pact with North Korea to come to their defense against enemy attacks and that would eliminate the need of North Korea to have a nuclear weapons arsenal.  But that wouldn't happen because North Korea enjoys the imagery of a world nuclear power.  Their hostile personality and puerile videos of giggling dictator and military generals is scary.  I wouldn't trust them with nuclear weapons and nobody else should.
Why not promise to help them become a world economic power with trade and skills training for the world trade like China has in exchange for nuclear weapons?  China should be able to do this.