`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
```
key.setObject();
        key.pushKV("scriptPubKey", HexStr(GetScriptForRawPubKey(coinbaseKey.GetPubKey())));
        key.pushKV("timestamp", 0);
        key.pushKV("internal", UniValue(true));
        keys.push_back(key);
        key.clear();
        key.setObject();
        CKey futureKey;
        futureKey.MakeNewKey(true);
        key.pushKV("scriptPubKey", HexStr(GetScriptForRawPubKey(futureKey.GetPubKey())));
        key.pushKV("timestamp", newTip->GetBlockTimeMax() + TIMESTAMP_WINDOW + 1);
        key.pushKV("internal", UniValue(true));
        keys.push_back(key);
        JSONRPCRequest request;
        request.params.setArray();
        request.params.push_back(keys);
        UniValue response = importmulti(request);
        BOOST_CHECK_EQUAL(response.write(),
            strprintf("[{\"success\":false,\"error\":{\"code\":-1,\"message\":\"Rescan failed for key with creation "
                      "timestamp %d. There was an error reading a block from time %d, which is after or within %d "
                      "seconds of key creation, and could contain transactions pertaining to the key. As a result, "
                      "transactions and coins using this key may not appear in the wallet. This error could be caused "
                      "by pruning or data corruption (see bitcoind log for details) and could be dealt with by "
                      "downloading and rescanning the relevant blocks (see -reindex and -rescan "
                      "options).\"}},{\"success\":true}]",
                              0, oldTip->GetBlockTimeMax(), TIMESTAMP_WINDOW));
        RemoveWallet(wallet);
    }
}
BOOST_FIXTURE_TEST_CASE(importwallet_rescan, TestChain100Setup)