`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`.)
CValidationState state;
    const CChainParams& chainparams = Params();
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::ALWAYS)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
    }
}
void PruneAndFlush() {
    CValidationState state;
    fCheckForPruning = true;
    const CChainParams& chainparams = Params();
    if (!FlushStateToDisk(chainparams, state, FlushStateMode::NONE)) {
        LogPrintf("%s: failed to flush state (%s)\n", __func__, FormatStateMessage(state));
    }
}
static void DoWarning(const std::string& strWarning)
{
    static bool fWarned = false;
    SetMiscWarning(strWarning);
    if (!fWarned) {
        AlertNotify(strWarning);
        fWarned = true;
    }
}
static void AppendWarning(std::string& res, const std::string& warn)