`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`.)
private:
    std::vector<PerBlockConnectTrace> blocksConnected;
    CTxMemPool &pool;
    boost::signals2::scoped_connection m_connNotifyEntryRemoved;
public:
    explicit ConnectTrace(CTxMemPool &_pool) : blocksConnected(1), pool(_pool) {
        m_connNotifyEntryRemoved = pool.NotifyEntryRemoved.connect(std::bind(&ConnectTrace::NotifyEntryRemoved, this, std::placeholders::_1, std::placeholders::_2));
    }
    void BlockConnected(CBlockIndex* pindex, std::shared_ptr<const CBlock> pblock) {
        assert(!blocksConnected.back().pindex);
        assert(pindex);
        assert(pblock);
        blocksConnected.back().pindex = pindex;
        blocksConnected.back().pblock = std::move(pblock);
        blocksConnected.emplace_back();
    }
    std::vector<PerBlockConnectTrace>& GetBlocksConnected() {