  Motivated by recent experiments [Zhang \textit{et al.}, Phys. Rev. Lett.
\textbf{95}, 216801 (2005) and Ellenberger \textit{et al.}, cond-mat/0602271]
reporting novel ringlike structures in the density--magnetic-field
($n_{2D}$\emph{--B}) diagrams of the longitudinal resistivity $\rho_{xx}$ of
quantum wells with two subbands, we investigate theoretically here the
magneto-transport properties of these quantum-Hall systems. We determine
$\rho_{xx}$ via both the Hartree and the Kohn-Sham self-consistent schemes plus
the Kubo formula. While the Hartree calculation yields diamond-shaped
structures in the $n_{2D}$\emph{--B} diagram, the calculation including
exchange and correlation effects (Kohn-Sham) more closely reproduces the
ringlike structures in the experiments.
