`RewindBlockIndex` reads `chainActive` (via `ChainActive()`) without holding `cs_main`:

https://github.com/bitcoin/bitcoin/blob/b2a6b0216192b6e8428f1a80b47f5178fccb961a/src/validation.cpp#L4314-L4331

(Please note that callers of `RewindBlockIndex` are _not_ allowed to hold `cs_main` since `RewindBlockIndex` indirectly calls `LimitValidationInterfaceQueue`.)
if (!g_chainstate.RewindBlockIndex(params)) {
        return false;
    }
    if (::ChainActive().Tip() != nullptr) {
        
        
        
        CValidationState state;
        if (!FlushStateToDisk(params, state, FlushStateMode::ALWAYS)) {
            LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", FormatStateMessage(state));
            return false;
        }
    }
    return true;
}
void CChainState::UnloadBlockIndex() {