`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);
    assert(lp);
    
    
    if (lp->maxInputBlock) {
        
        
        if (!::ChainActive().Contains(lp->maxInputBlock)) {
            return false;
        }
    }
    
    return true;
}
bool CheckSequenceLocks(const CTxMemPool& pool, const CTransaction& tx, int flags, LockPoints* lp, bool useExistingLockPoints)