Spin diffusion in spin glasses requires two magnetic variables, $\vec{M}$ and $\vec{m}$

Experiment has established that spin glasses can support a steady-state spin current ${\vec{j}}_i$. However, the accepted theory of spin-glass dynamics permits oscillations but no steady-state spin current. Onsager's irreversible thermodynamics implies that the spin current is proportional to the gradient of a magnetization. We argue, however, that the magnon distribution function associated with the local equilibrium magnetization $\vec{M}$ cannot diffuse because it represents ${10}^{23}$ variables. We therefore invoke the nonequilibrium magnetization $\vec{m}$, which in spintronics is called the spin accumulation. Applying the theory of irreversible thermodynamics, we indeed find that it predicts spin diffusion, and we consider other experimental consequences of the theory, including a wavelength-dependent coupling between the reactive and the diffusive degrees of freedom.