`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
```
{
    AssertLockHeld(cs_wallet);
    for (std::set<COutPoint>::iterator it = setLockedCoins.begin();
         it != setLockedCoins.end(); it++) {
        COutPoint outpt = (*it);
        vOutpts.push_back(outpt);
    }
}
 
void CWallet::GetKeyBirthTimes(interfaces::Chain::Lock& locked_chain, std::map<CKeyID, int64_t>& mapKeyBirth) const {
    AssertLockHeld(cs_wallet);
    mapKeyBirth.clear();
    
    for (const auto& entry : mapKeyMetadata) {
        if (entry.second.nCreateTime) {
            mapKeyBirth[entry.first] = entry.second.nCreateTime;
        }
    }
    
    const Optional<int> tip_height = locked_chain.getHeight();
    const int max_height = tip_height && *tip_height > 144 ? *tip_height - 144 : 0; 
    std::map<CKeyID, int> mapKeyFirstBlock;
    for (const CKeyID &keyid : GetKeys()) {
        if (mapKeyBirth.count(keyid) == 0)
            mapKeyFirstBlock[keyid] = max_height;