`LockAnnotation lock(::cs_main)` is a guarantee to the compiler thread analysis that `::cs_main` is locked (when it couldn't be determined otherwise).

Despite being annotated with the locking guarantee ...

https://github.com/bitcoin/bitcoin/blob/65526fc8666fef35ef908dbc225f706bef642c7e/src/interfaces/chain.cpp#L134-L138

... `getTipLocator()` reads `chainActive` (via `::ChainActive()`) without holding `cs_main`.

This can be verified by adding the following `AssertLockHeld(cs_main)`:

```
$ git diff
diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
index 59623284d..9fc693a0f 100644
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -134,6 +134,7 @@ class LockImpl : public Chain::Lock
     CBlockLocator getTipLocator() override
     {
         LockAnnotation lock(::cs_main);
+        AssertLockHeld(::cs_main);
         return ::ChainActive().GetLocator();
     }
     Optional<int> findLocatorFork(const CBlockLocator& locator) override
$ make check
../build-aux/test-driver: line 107: 12881 Aborted                 "$@" > $log_file 2>&1
FAIL: qt/test/test_bitcoin-qt
```
if (nMaxFee > HIGH_MAX_TX_FEE) {
            chain.initWarning(_("-maxtxfee is set very high! Fees this large could be paid on a single transaction."));
        }
        if (CFeeRate(nMaxFee, 1000) < chain.relayMinFee()) {
            chain.initError(strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s' (must be at least the minrelay fee of %s to prevent stuck transactions)"),
                                       gArgs.GetArg("-maxtxfee", ""), chain.relayMinFee().ToString()));
            return nullptr;
        }
        walletInstance->m_default_max_tx_fee = nMaxFee;
    }
    if (chain.relayMinFee().GetFeePerK() > HIGH_TX_FEE_PER_KB)
        chain.initWarning(AmountHighWarn("-minrelaytxfee") + " " +
                    _("The wallet will avoid paying less than the minimum relay fee."));
    walletInstance->m_confirm_target = gArgs.GetArg("-txconfirmtarget", DEFAULT_TX_CONFIRM_TARGET);
    walletInstance->m_spend_zero_conf_change = gArgs.GetBoolArg("-spendzeroconfchange", DEFAULT_SPEND_ZEROCONF_CHANGE);
    walletInstance->m_signal_rbf = gArgs.GetBoolArg("-walletrbf", DEFAULT_WALLET_RBF);
    walletInstance->WalletLogPrintf("Wallet completed loading in %15dms\n", GetTimeMillis() - nStart);
    
    walletInstance->TopUpKeyPool();
    auto locked_chain = chain.lock();
    LOCK(walletInstance->cs_wallet);
    int rescan_height = 0;
    if (!gArgs.GetBoolArg("-rescan", false))
    {
        WalletBatch batch(*walletInstance->database);
        CBlockLocator locator;
        if (batch.ReadBestBlock(locator)) {
            if (const Optional<int> fork_height = locked_chain->findLocatorFork(locator)) {
                rescan_height = *fork_height;
            }