`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 (!ParseMoney(gArgs.GetArg("-mintxfee", ""), n) || 0 == n) {
            chain.initError(AmountErrMsg("mintxfee", gArgs.GetArg("-mintxfee", "")));
            return nullptr;
        }
        if (n > HIGH_TX_FEE_PER_KB) {
            chain.initWarning(AmountHighWarn("-mintxfee") + " " +
                              _("This is the minimum transaction fee you pay on every transaction."));
        }
        walletInstance->m_min_fee = CFeeRate(n);
    }
    walletInstance->m_allow_fallback_fee = Params().IsFallbackFeeEnabled();
    if (gArgs.IsArgSet("-fallbackfee")) {
        CAmount nFeePerK = 0;
        if (!ParseMoney(gArgs.GetArg("-fallbackfee", ""), nFeePerK)) {
            chain.initError(strprintf(_("Invalid amount for -fallbackfee=<amount>: '%s'"), gArgs.GetArg("-fallbackfee", "")));
            return nullptr;
        }
        if (nFeePerK > HIGH_TX_FEE_PER_KB) {
            chain.initWarning(AmountHighWarn("-fallbackfee") + " " +
                              _("This is the transaction fee you may pay when fee estimates are not available."));
        }
        walletInstance->m_fallback_fee = CFeeRate(nFeePerK);
        walletInstance->m_allow_fallback_fee = nFeePerK != 0; 
    }
    if (gArgs.IsArgSet("-discardfee")) {
        CAmount nFeePerK = 0;
        if (!ParseMoney(gArgs.GetArg("-discardfee", ""), nFeePerK)) {
            chain.initError(strprintf(_("Invalid amount for -discardfee=<amount>: '%s'"), gArgs.GetArg("-discardfee", "")));
            return nullptr;
        }