init.cpp:1635 prints mapBlockIndex.size() without cs_main. This is technically a race (though it is rather inconsequential). At some point someone should fix this so tsan stops complaining.
bool fNotify = false;
    bool fInitialBlockDownload = false;
    static CBlockIndex* pindexHeaderOld = nullptr;
    CBlockIndex* pindexHeader = nullptr;
    {
        LOCK(cs_main);
        pindexHeader = pindexBestHeader;
        if (pindexHeader != pindexHeaderOld) {
            fNotify = true;
            fInitialBlockDownload = IsInitialBlockDownload();
            pindexHeaderOld = pindexHeader;
        }
    }
    
    if (fNotify) {
        uiInterface.NotifyHeaderTip(fInitialBlockDownload, pindexHeader);
    }
}
/**
 * Make the best chain active, in multiple steps. The result is either failure
 * or an activated best chain. pblock is either nullptr or a pointer to a block
 * that is already loaded (to avoid loading it again from disk).
 */
bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) {