LoadChainTip requires cs_main to be locked. Under some conditions, it may call ActivateBestChain. However, ActivateBestChain requires cs_main NOT to be taken when called.
if (!AcceptBlockHeader(block, state, chainparams, &pindex))
        return false;
    
    
    
    bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
    bool fHasMoreOrSameWork = (m_chain.Tip() ? pindex->nChainWork >= m_chain.Tip()->nChainWork : true);
    
    
    
    
    
    bool fTooFarAhead = (pindex->nHeight > int(m_chain.Height() + MIN_BLOCKS_TO_KEEP));
    
    
    
    
    
    
    if (fAlreadyHave) return true;
    if (!fRequested) {  
        if (pindex->nTx != 0) return true;    
        if (!fHasMoreOrSameWork) return true; 
        if (fTooFarAhead) return true;        
        
        
        
        
        if (pindex->nChainWork < nMinimumChainWork) return true;
    }