`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`.)
{
    AssertLockHeld(cs_main);
    
    
    for (const uint256& hash : locator.vHave) {
        CBlockIndex* pindex = LookupBlockIndex(hash);
        if (pindex) {
            if (chain.Contains(pindex))
                return pindex;
            if (pindex->GetAncestor(chain.Height()) == chain.Tip()) {
                return chain.Tip();
            }
        }
    }
    return chain.Genesis();
}
std::unique_ptr<CCoinsViewDB> pcoinsdbview;
std::unique_ptr<CCoinsViewCache> pcoinsTip;
std::unique_ptr<CBlockTreeDB> pblocktree;
enum class FlushStateMode {