`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
```
{
    std::vector<std::string> values;
    for (const auto& address : mapAddressBook) {
        for (const auto& data : address.second.destdata) {
            if (!data.first.compare(0, prefix.size(), prefix)) {
                values.emplace_back(data.second);
            }
        }
    }
    return values;
}
void CWallet::MarkPreSplitKeys()
{
    WalletBatch batch(*database);
    for (auto it = setExternalKeyPool.begin(); it != setExternalKeyPool.end();) {
        int64_t index = *it;
        CKeyPool keypool;
        if (!batch.ReadPool(index, keypool)) {
            throw std::runtime_error(std::string(__func__) + ": read keypool entry failed");
        }
        keypool.m_pre_split = true;
        if (!batch.WritePool(index, keypool)) {
            throw std::runtime_error(std::string(__func__) + ": writing modified keypool entry failed");
        }
        set_pre_split_keypool.insert(index);
        it = setExternalKeyPool.erase(it);
    }
}
bool CWallet::Verify(interfaces::Chain& chain, const WalletLocation& location, bool salvage_wallet, std::string& error_string, std::string& warning_string)