diff --git a/test/cpp/end2end/xds_end2end_test.cc b/test/cpp/end2end/xds_end2end_test.cc
index e2a0fed5f50..3daf1a43e19 100644
--- a/test/cpp/end2end/xds_end2end_test.cc
+++ b/test/cpp/end2end/xds_end2end_test.cc
@@ -306,8 +306,8 @@ class CountedService : public ServiceType {
 
  private:
   grpc_core::Mutex mu_;
-  size_t request_count_ = 0;
-  size_t response_count_ = 0;
+  size_t request_count_ ABSL_GUARDED_BY(mu_) = 0;
+  size_t response_count_ ABSL_GUARDED_BY(mu_) = 0;
 };
 
 template <typename RpcService>
@@ -360,8 +360,8 @@ class BackendServiceImpl
 
  private:
   grpc_core::Mutex mu_;
-  std::set<std::string> clients_;
-  std::vector<std::string> last_peer_identity_;
+  std::set<std::string> clients_ ABSL_GUARDED_BY(mu_);
+  std::vector<std::string> last_peer_identity_ ABSL_GUARDED_BY(mu_);
 };
 
 class ClientStats {
@@ -643,7 +643,7 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
     NotifyDoneWithAdsCallLocked();
   }
 
-  void NotifyDoneWithAdsCallLocked() {
+  void NotifyDoneWithAdsCallLocked() ABSL_EXCLUSIVE_LOCKS_REQUIRED(ads_mu_) {
     if (!ads_done_) {
       ads_done_ = true;
       ads_cond_.SignalAll();
@@ -830,6 +830,28 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
     }
 
    private:
+    // NB: clang's annotalysis is confused by the use of inner template
+    // classes here and *ignores* the exclusive lock annotation on some
+    // functions. See https://bugs.llvm.org/show_bug.cgi?id=51368.
+    //
+    // This class is used for a dual purpose:
+    // - it convinces clang that the lock is held in a given scope
+    // - when used in a function that is annotated to require the inner lock it
+    //   will cause compilation to fail if the upstream bug is fixed!
+    //
+    // If you arrive here because of a compilation failure, that might mean the
+    // clang bug is fixed! Please report that on the ticket.
+    //
+    // Since the buggy compiler will still need to be supported, consider
+    // wrapping this class in a compiler version #if and replace its usage
+    // with a macro whose expansion is conditional on the compiler version. In
+    // time (years? decades?) this code can be deleted altogether.
+    class ABSL_SCOPED_LOCKABLE NoopMutexLock {
+     public:
+      explicit NoopMutexLock(grpc_core::Mutex& mu)
+          ABSL_EXCLUSIVE_LOCK_FUNCTION(mu) {}
+      ~NoopMutexLock() ABSL_UNLOCK_FUNCTION() {}
+    };
     // Processes a response read from the client.
     // Populates response if needed.
     void ProcessRequest(const DiscoveryRequest& request,
@@ -837,7 +859,9 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
                         UpdateQueue* update_queue,
                         SubscriptionMap* subscription_map,
                         SentState* sent_state,
-                        absl::optional<DiscoveryResponse>* response) {
+                        absl::optional<DiscoveryResponse>* response)
+        ABSL_EXCLUSIVE_LOCKS_REQUIRED(parent_->ads_mu_) {
+      NoopMutexLock mu(parent_->ads_mu_);
       // Check the nonce sent by the client, if any.
       // (This will be absent on the first request on a stream.)
       if (request.response_nonce().empty()) {
@@ -936,7 +960,9 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
     void ProcessUpdate(const std::string& resource_type,
                        const std::string& resource_name,
                        SubscriptionMap* subscription_map, SentState* sent_state,
-                       absl::optional<DiscoveryResponse>* response) {
+                       absl::optional<DiscoveryResponse>* response)
+        ABSL_EXCLUSIVE_LOCKS_REQUIRED(parent_->ads_mu_) {
+      NoopMutexLock mu(parent_->ads_mu_);
       const std::string v2_resource_type = TypeUrlToV2(resource_type);
       gpr_log(GPR_INFO, "ADS[%p]: Received update for type=%s name=%s", this,
               resource_type.c_str(), resource_name.c_str());
@@ -996,7 +1022,9 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
         const std::string& resource_type, const std::string& v2_resource_type,
         const int version, const SubscriptionNameMap& subscription_name_map,
         const std::set<std::string>& resources_added_to_response,
-        SentState* sent_state, DiscoveryResponse* response) {
+        SentState* sent_state, DiscoveryResponse* response)
+        ABSL_EXCLUSIVE_LOCKS_REQUIRED(parent_->ads_mu_) {
+      NoopMutexLock mu(parent_->ads_mu_);
       auto& response_state =
           parent_->resource_type_response_state_[resource_type];
       if (response_state.state == ResponseState::NOT_SENT) {
@@ -1140,22 +1168,23 @@ class AdsServiceImpl : public std::enable_shared_from_this<AdsServiceImpl> {
   std::atomic_bool seen_v3_client_{false};
 
   grpc_core::CondVar ads_cond_;
-  // Protect the members below.
   grpc_core::Mutex ads_mu_;
-  bool ads_done_ = false;
+  bool ads_done_ ABSL_GUARDED_BY(ads_mu_) = false;
   std::map<std::string /* type_url */, ResponseState>
-      resource_type_response_state_;
-  std::set<std::string /*resource_type*/> resource_types_to_ignore_;
-  std::map<std::string /*resource_type*/, int> resource_type_min_versions_;
+      resource_type_response_state_ ABSL_GUARDED_BY(ads_mu_);
+  std::set<std::string /*resource_type*/> resource_types_to_ignore_
+      ABSL_GUARDED_BY(ads_mu_);
+  std::map<std::string /*resource_type*/, int> resource_type_min_versions_
+      ABSL_GUARDED_BY(ads_mu_);
   // An instance data member containing the current state of all resources.
   // Note that an entry will exist whenever either of the following is true:
   // - The resource exists (i.e., has been created by SetResource() and has not
   //   yet been destroyed by UnsetResource()).
   // - There is at least one subscription for the resource.
-  ResourceMap resource_map_;
+  ResourceMap resource_map_ ABSL_GUARDED_BY(ads_mu_);
 
   grpc_core::Mutex clients_mu_;
-  std::set<std::string> clients_;
+  std::set<std::string> clients_ ABSL_GUARDED_BY(clients_mu_);
 };
 
 class LrsServiceImpl : public std::enable_shared_from_this<LrsServiceImpl> {
@@ -1193,9 +1222,15 @@ class LrsServiceImpl : public std::enable_shared_from_this<LrsServiceImpl> {
     cluster_names_ = cluster_names;
   }
 
-  void Start() {
-    lrs_done_ = false;
-    result_queue_.clear();
+  void Start() ABSL_LOCKS_EXCLUDED(lrs_mu_, load_report_mu_) {
+    {
+      grpc_core::MutexLock lock(&lrs_mu_);
+      lrs_done_ = false;
+    }
+    {
+      grpc_core::MutexLock lock(&load_report_mu_);
+      result_queue_.clear();
+    }
   }
 
   void Shutdown() {
@@ -1292,7 +1327,7 @@ class LrsServiceImpl : public std::enable_shared_from_this<LrsServiceImpl> {
     LrsServiceImpl* parent_;
   };
 
-  void NotifyDoneWithLrsCallLocked() {
+  void NotifyDoneWithLrsCallLocked() ABSL_EXCLUSIVE_LOCKS_REQUIRED(lrs_mu_) {
     if (!lrs_done_) {
       lrs_done_ = true;
       lrs_cv_.SignalAll();
@@ -1313,12 +1348,14 @@ class LrsServiceImpl : public std::enable_shared_from_this<LrsServiceImpl> {
   std::set<std::string> cluster_names_;
 
   grpc_core::CondVar lrs_cv_;
-  grpc_core::Mutex lrs_mu_;  // Protects lrs_done_.
-  bool lrs_done_ = false;
-
-  grpc_core::Mutex load_report_mu_;  // Protects the members below.
-  grpc_core::CondVar* load_report_cond_ = nullptr;
-  std::deque<std::vector<ClientStats>> result_queue_;
+  grpc_core::Mutex lrs_mu_;
+  bool lrs_done_ ABSL_GUARDED_BY(lrs_mu_) = false;
+
+  grpc_core::Mutex load_report_mu_;
+  grpc_core::CondVar* load_report_cond_ ABSL_GUARDED_BY(load_report_mu_) =
+      nullptr;
+  std::deque<std::vector<ClientStats>> result_queue_
+      ABSL_GUARDED_BY(load_report_mu_);
 };
 
 class TestType {
@@ -2472,7 +2509,7 @@ class XdsEnd2endTest : public ::testing::TestWithParam<TestType> {
    private:
     grpc_core::Mutex mu_;
     grpc_core::CondVar cond_;
-    std::map<std::string, grpc::Status> status_map;
+    std::map<std::string, grpc::Status> status_map ABSL_GUARDED_BY(mu_);
   };
 
   class ServerThread {