diff --git a/src/replica/duplication/replica_duplicator_manager.cpp b/src/replica/duplication/replica_duplicator_manager.cpp
index 4bdc58f320..b0a02b4b45 100644
--- a/src/replica/duplication/replica_duplicator_manager.cpp
+++ b/src/replica/duplication/replica_duplicator_manager.cpp
@@ -102,6 +102,7 @@ replica_duplicator_manager::get_duplication_confirms_to_update() const
 
 void replica_duplicator_manager::sync_duplication(const duplication_entry &ent)
 {
+    zauto_lock l(_lock);
     auto it = ent.progress.find(get_gpid().get_partition_index());
     if (it == ent.progress.end()) {
         // Inconsistent with the meta server.
@@ -109,8 +110,6 @@ void replica_duplicator_manager::sync_duplication(const duplication_entry &ent)
         return;
     }
 
-    zauto_lock l(_lock);
-
     dupid_t dupid = ent.dupid;
     duplication_status::type next_status = ent.status;
 
@@ -183,7 +182,6 @@ void replica_duplicator_manager::update_confirmed_decree_if_secondary(decree con
         return;
     }
 
-    zauto_lock l(_lock);
     remove_all_duplications();
     if (confirmed >= 0) { // duplication ongoing
         // confirmed decree never decreases
@@ -197,7 +195,8 @@ void replica_duplicator_manager::update_confirmed_decree_if_secondary(decree con
 
 void replica_duplicator_manager::METRIC_FUNC_NAME_SET(dup_pending_mutations)()
 {
-    int64_t total = 0;
+    zauto_lock l(_lock);
+    uint64_t total = 0;
     for (const auto &dup : _duplications) {
         total += dup.second->get_pending_mutations_count();
     }
@@ -227,6 +226,7 @@ replica_duplicator_manager::get_dup_states() const
 
 void replica_duplicator_manager::remove_all_duplications()
 {
+    zauto_lock l(_lock);
     // fast path
     if (_duplications.empty()) {
         return;
diff --git a/src/task/task.h b/src/task/task.h
index 49a5ba05dc..22c16c8036 100644
--- a/src/task/task.h
+++ b/src/task/task.h
@@ -48,6 +48,7 @@
 #include "utils/fmt_logging.h"
 #include "utils/join_point.h"
 #include "utils/ports.h"
+#include "utils/synchronize.h"
 #include "utils/utils.h"
 
 namespace dsn {
@@ -329,6 +330,11 @@ class raw_task : public task
         : task(code, hash, node), _cb(std::move(cb))
     {
     }
+    ~raw_task() override
+    {
+        ::dsn::utils::auto_lock<::dsn::utils::ex_lock_nr> l(_lock);
+        _cb = nullptr;
+    }
 
     void exec() override
     {
@@ -338,10 +344,13 @@ class raw_task : public task
     }
 
 protected:
-    void clear_non_trivial_on_task_end() override { _cb = nullptr; }
-
-protected:
+    void clear_non_trivial_on_task_end() override
+    {
+        ::dsn::utils::auto_lock<::dsn::utils::ex_lock_nr> l(_lock);
+        _cb = nullptr;
+    }
     task_handler _cb;
+    ::dsn::utils::ex_lock_nr _lock;
 };
 
 //----------------- timer task -------------------------------------------------------