  Integrated sensing and communication (ISAC) has emerged as a promising
technology to facilitate high-rate communications and super-resolution sensing,
particularly operating in the millimeter wave (mmWave) band. However, the
vulnerability of mmWave signals to blockages severely impairs ISAC capabilities
and coverage. To tackle this, an efficient and low-cost solution is to deploy
distributed reconfigurable intelligent surfaces (RISs) to construct virtual
links between the base stations (BSs) and users in a controllable fashion. In
this paper, we investigate the generalized RIS-assisted mmWave ISAC networks
considering the blockage effect, and examine the beneficial impact of RISs on
the coverage rate utilizing stochastic geometry. Specifically, taking into
account the coupling effect of ISAC dual functions within the same network
topology, we derive the conditional coverage probability of ISAC performance
for two association cases, based on the proposed beam pattern model and user
association policies. Then, the marginal coverage rate is calculated by
combining these two cases through the distance-dependent thinning method.
Simulation results verify the accuracy of derived theoretical formulations and
provide valuable guidelines for the practical network deployment. Specifically,
our results indicate the superiority of the RIS deployment with the density of
40 km${}^{-2}$ BSs, and that the joint coverage rate of ISAC performance
exhibits potential growth from $67.1\%$ to $92.2\%$ with the deployment of
RISs.
