`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.LoadBlockIndex(chainparams.GetConsensus(), *pblocktree))
        return false;
    
    pblocktree->ReadLastBlockFile(nLastBlockFile);
    vinfoBlockFile.resize(nLastBlockFile + 1);
    LogPrintf("%s: last block file = %i\n", __func__, nLastBlockFile);
    for (int nFile = 0; nFile <= nLastBlockFile; nFile++) {
        pblocktree->ReadBlockFileInfo(nFile, vinfoBlockFile[nFile]);
    }
    LogPrintf("%s: last block file info: %s\n", __func__, vinfoBlockFile[nLastBlockFile].ToString());
    for (int nFile = nLastBlockFile + 1; true; nFile++) {
        CBlockFileInfo info;
        if (pblocktree->ReadBlockFileInfo(nFile, info)) {
            vinfoBlockFile.push_back(info);
        } else {
            break;