Travis Barker Performs With MGK at Forum, Fully Back After Hospitalization

Travis Barker is fully back after a major health scare ... he jumped on stage with his bud Machine Gun Kelly to perform at a wild concert.

Travis took to the drums Wednesday night at The Forum in Inglewood during MGK's show -- part of Kelly's Mainstream Sellout tour. Trav got roaring cheers as he walked on stage, shirtless of course.

MGK also calls out their online haters before rockin' out, saying "If we would've listened to what the Internet f***ing said about us, we would've never made this album."

Willow and Avril Lavigne also got in the act ... quite the night for fans.

As we reported, Travis has been moving back into business mode ever since he was released from the hospital ... shortly after his release he headed into a Calabasas studio to record some tunes.