The Barbarian 1st level ability Rage states:
If you are able to cast spells, you can’t cast them or concentrate on them while raging.
And the Variant Human: Mark of Making innate ability Spellsmith states:
You know the mending cantrip. You can also cast the magic weapon spell with this trait. When you do so, the spell lasts for 1 hour and doesn’t require concentration. Once you cast the spell with this trait, you can’t do so again until you finish a long rest. Intelligence is your spellcasting ability for these spells.
If I cast magic weapon first with Spellsmith, and then Rage, will it cancel magic weapon even though I don't have to concentrate on it?