Most tents don’t smell very fresh when you first pull it out of the bag. If you pull your tent out and it smells like puke them you have a real problem.
That very bad oder is the smell of moisture breaking down the waterproof coating. Even a small amount of condensation can cause mildew to grow, so never store a wet tent. After a rainy or humid night, drape the fly over a tree and turn the tent on its side to let the sun dry the bottom. Once you get home, hang the tent on a clothesline or shower rod. Once it’s dry, store it loosely in a cotton pillowcase or mesh storage sack.
Those small steps will make a vast improvement on the oder coming from your tent on your next camping or backpacking trip.