`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
```
double guessVerificationProgress(const uint256& block_hash) override
    {
        LOCK(cs_main);
        return GuessVerificationProgress(Params().TxData(), LookupBlockIndex(block_hash));
    }
    RBFTransactionState isRBFOptIn(const CTransaction& tx) override
    {
        LOCK(::mempool.cs);
        return IsRBFOptIn(tx, ::mempool);
    }
    bool hasDescendantsInMempool(const uint256& txid) override
    {
        LOCK(::mempool.cs);
        auto it = ::mempool.GetIter(txid);
        return it && (*it)->GetCountWithDescendants() > 1;
    }
    void relayTransaction(const uint256& txid) override
    {
        CInv inv(MSG_TX, txid);
        g_connman->ForEachNode([&inv](CNode* node) { node->PushInventory(inv); });
    }
    void getTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants) override
    {
        ::mempool.GetTransactionAncestry(txid, ancestors, descendants);
    }
    bool checkChainLimits(const CTransactionRef& tx) override