`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
```
if (block_hash == stop_block) {
            break;
        }
        {
            auto locked_chain = chain().lock();
            Optional<int> tip_height = locked_chain->getHeight();
            if (!tip_height || *tip_height <= block_height || !locked_chain->getBlockHeight(block_hash)) {
                
                
                break;
            }
            
            block_hash = locked_chain->getBlockHash(++*block_height);
            progress_current = chain().guessVerificationProgress(block_hash);
            
            const uint256 prev_tip_hash = tip_hash;
            tip_hash = locked_chain->getBlockHash(*tip_height);
            if (stop_block.IsNull() && prev_tip_hash != tip_hash) {
                
                progress_end = chain().guessVerificationProgress(tip_hash);
            }
        }
    }
    ShowProgress(strprintf("%s " + _("Rescanning..."), GetDisplayName()), 100); 
    if (block_height && fAbortRescan) {
        WalletLogPrintf("Rescan aborted at block %d. Progress=%f\n", *block_height, progress_current);
        result.status = ScanResult::USER_ABORT;
    } else if (block_height && chain().shutdownRequested()) {
        WalletLogPrintf("Rescan interrupted by shutdown request at block %d. Progress=%f\n", *block_height, progress_current);
        result.status = ScanResult::USER_ABORT;