`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
```
wallet->AddKeyPubKey(coinbaseKey, coinbaseKey.GetPubKey());
        JSONRPCRequest request;
        request.params.setArray();
        request.params.push_back(backup_file);
        AddWallet(wallet);
        ::dumpwallet(request);
        RemoveWallet(wallet);
    }
    
    
    {
        std::shared_ptr<CWallet> wallet = std::make_shared<CWallet>(chain.get(), WalletLocation(), WalletDatabase::CreateDummy());
        JSONRPCRequest request;
        request.params.setArray();
        request.params.push_back(backup_file);
        AddWallet(wallet);
        ::importwallet(request);
        RemoveWallet(wallet);
        LOCK(wallet->cs_wallet);
        BOOST_CHECK_EQUAL(wallet->mapWallet.size(), 3U);
        BOOST_CHECK_EQUAL(m_coinbase_txns.size(), 103U);
        for (size_t i = 0; i < m_coinbase_txns.size(); ++i) {
            bool found = wallet->GetWalletTx(m_coinbase_txns[i]->GetHash());
            bool expected = i >= 100;
            BOOST_CHECK_EQUAL(found, expected);
        }
    }
    SetMockTime(0);
}
BOOST_FIXTURE_TEST_CASE(coin_mark_dirty_immature_credit, TestChain100Setup)