diff --git a/src/nameserver/chunkserver_manager.cc b/src/nameserver/chunkserver_manager.cc
index 4233b780..7156a5c6 100644
--- a/src/nameserver/chunkserver_manager.cc
+++ b/src/nameserver/chunkserver_manager.cc
@@ -627,15 +627,18 @@ void ChunkServerManager::LogStats() {
     int32_t w_qps = 0, r_qps = 0;
     int64_t w_speed = 0, r_speed = 0, recover_speed = 0;
     int32_t overload = 0;
-    for (ServerMap::iterator it = chunkservers_.begin(); it != chunkservers_.end(); ++it) {
-        ChunkServerInfo* cs = it->second;
-        w_qps += cs->w_qps();
-        w_speed += cs->w_speed();
-        r_qps += cs->r_qps();
-        r_speed += cs->r_speed();
-        recover_speed += cs->recover_speed();
-        if (cs->load() > kChunkServerLoadMax) {
-            ++overload;
+    {
+        MutexLock lock(&mu_);
+        for (ServerMap::iterator it = chunkservers_.begin(); it != chunkservers_.end(); ++it) {
+            ChunkServerInfo* cs = it->second;
+            w_qps += cs->w_qps();
+            w_speed += cs->w_speed();
+            r_qps += cs->r_qps();
+            r_speed += cs->r_speed();
+            recover_speed += cs->recover_speed();
+            if (cs->load() > kChunkServerLoadMax) {
+                ++overload;
+            }
         }
     }
     stats_.w_qps = w_qps;