`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
```
wtx.m_it_wtxOrdered = wtxOrdered.insert(std::make_pair(wtx.nOrderPos, &wtx));
        wtx.nTimeSmart = ComputeTimeSmart(wtx);
        AddToSpends(hash);
    }
    bool fUpdated = false;
    if (!fInsertedNew)
    {
        
        if (!wtxIn.hashUnset() && wtxIn.hashBlock != wtx.hashBlock)
        {
            wtx.hashBlock = wtxIn.hashBlock;
            fUpdated = true;
        }
        
        if (wtxIn.hashBlock.IsNull() && wtx.isAbandoned())
        {
            wtx.hashBlock = wtxIn.hashBlock;
            fUpdated = true;
        }
        if (wtxIn.nIndex != -1 && (wtxIn.nIndex != wtx.nIndex))
        {
            wtx.nIndex = wtxIn.nIndex;
            fUpdated = true;
        }
        if (wtxIn.fFromMe && wtxIn.fFromMe != wtx.fFromMe)
        {
            wtx.fFromMe = wtxIn.fFromMe;
            fUpdated = true;
        }