  Light mesons $(\sigma, \pi^0, \pi^\pm)$ are investigated in
$T-\mu_B-\mu_I-eB$ space by using a two-flavor NJL model, which are related to
the chiral symmetry restoration and pion superfluid phase transition. In
$T-\mu_B-eB$ space, during the chiral restoration process, the mass of
pseudo-Goldstone mode $\pi^0$ keeps increasing, together with the sudden mass
jump. At the critical end point region, $\pi^0$ meson has a very sharp but
continuous mass increase, together with a sudden mass jump at the Mott
transition, and in the first order chiral phase transition region nearby, we
observe twice $\pi^0$ mass jumps, induced by the Mott transition and quark mass
jump, respectively. The mass of Higgs mode $\sigma$ first decreases and then
increases associated with the chiral symmetry restoration, and shows a jump at
the first order chiral phase transition. We plot the chiral phase diagram in
terms of the change of quark mass, the Mott transition of $\pi^0$ and the
minimum mass of $\sigma$. Due to the explicit breaking of chiral symmetry in
physical case, the chiral restoration phase boundaries in $T-\mu_B$ plane from
the order parameter and meson side are different from each other. In $T-\mu_I$
plane, the competition between pion superfluid phase transition and chiral
symmetry restoration under magnetic fields is studied in terms of the Goldstone
mode $\pi^+$ and the pseudo-Goldstone mode $\pi^0$. The separation of the two
phase boundaries is enhanced by the external magnetic field. Different from the
twice mass jumps of $\pi^0$ in the first order chiral phase transition region,
the $\pi^+$ meson displays several mass jumps in the chiral crossover region.
At the critical end point, $\pi^+$ also shows very sharp but continuous mass
changes, together with a mass jump at the Mott transition.
