A hydrogen atom weighs 13.6eV less than a proton + electron. This missing energy, which is tiny compared to the rest mass of almost a GeV, was carried off by a photon when the atom formed.
Nuclei show a much more pronounced mass defect and can be "missing" up to 1% of their mass.
But the opposite is the case for the quarks in the proton. Together they are less than 2% of the proton's mass. And gluons are massless.
But "quark mass" is a misnomer: quarks cannot be isolated. The "mass" (I think) is a "bare mass" without any gluon field. Similarly, I would think an electron would weigh less when measured at higher energies (shorter lengths) which exclude the stress-energy in its surrounding electric field.
If "mass" is defined as the mass of free, isolated particles, than would the quark mass be infinite because it would take an infinite amount of energy to create a free quark? If so the proton would be a finite mass particle made out of infinite mass particles and thus very stable.
