fix deadlock

src/storage/ddl/ob_tablet_ddl_kv_mgr.cpp

@@ -96,7 +96,8 @@ int ObTabletDDLKvMgr::ddl_start(const ObITable::TableKey &table_key,
 {
   int ret = OB_SUCCESS;
   bool is_brand_new = false;
-  TCWLockGuard guard(lock_);
+  SCN saved_start_scn;
+  int64_t saved_snapshot_version = 0;
   if (OB_UNLIKELY(!is_inited_)) {
     ret = OB_NOT_INIT;
     LOG_WARN("not init", K(ret), K(is_inited_));
@@ -107,31 +108,39 @@ int ObTabletDDLKvMgr::ddl_start(const ObITable::TableKey &table_key,
   } else if (table_key.get_tablet_id() != tablet_id_) {
     ret = OB_ERR_SYS;
     LOG_WARN("tablet id not same", K(ret), K(table_key), K(tablet_id_));
-  } else if (start_scn_.is_valid_and_not_min()) {
-    if (execution_id >= execution_id_ && start_scn >= start_scn_) {
-      LOG_INFO("execution id changed, need cleanup", K(ls_id_), K(tablet_id_), K(execution_id_), K(execution_id), K(start_scn_), K(start_scn));
-      cleanup_unlock();
-      is_brand_new = true;
-    } else {
-      if (!checkpoint_scn.is_valid_and_not_min()) {
-        // only return error code when not start from checkpoint.
-        ret = OB_TASK_EXPIRED;
+  } else {
+    TCWLockGuard guard(lock_);
+    if (start_scn_.is_valid_and_not_min()) {
+      if (execution_id >= execution_id_ && start_scn >= start_scn_) {
+        LOG_INFO("execution id changed, need cleanup", K(ls_id_), K(tablet_id_), K(execution_id_), K(execution_id), K(start_scn_), K(start_scn));
+        cleanup_unlock();
+        is_brand_new = true;
+      } else {
+        if (!checkpoint_scn.is_valid_and_not_min()) {
+          // only return error code when not start from checkpoint.
+          ret = OB_TASK_EXPIRED;
+        }
+        LOG_INFO("ddl start ignored", K(ls_id_), K(tablet_id_), K(execution_id_), K(execution_id), K(start_scn_), K(start_scn));
       }
-      LOG_INFO("ddl start ignored", K(ls_id_), K(tablet_id_), K(execution_id_), K(execution_id), K(start_scn_), K(start_scn));
+    } else {
+      is_brand_new = true;
+    }
+    if (OB_SUCC(ret) && is_brand_new) {
+      table_key_ = table_key;
+      cluster_version_ = cluster_version;
+      execution_id_ = execution_id;
+      start_scn_ = start_scn;
+      max_freeze_scn_ = SCN::max(start_scn, checkpoint_scn);
+    }
+    if (OB_SUCC(ret)) {
+      // save variables under lock
+      saved_start_scn = start_scn_;
+      saved_snapshot_version = table_key_.get_snapshot_version();
     }
-  } else {
-    is_brand_new = true;
-  }
-  if (OB_SUCC(ret) && is_brand_new) {
-    table_key_ = table_key;
-    cluster_version_ = cluster_version;
-    execution_id_ = execution_id;
-    start_scn_ = start_scn;
-    max_freeze_scn_ = SCN::max(start_scn, checkpoint_scn);
   }
   if (OB_SUCC(ret) && !checkpoint_scn.is_valid_and_not_min()) {
     // remove ddl sstable if exists and flush ddl start log ts and snapshot version into tablet meta
-    if (OB_FAIL(update_tablet(start_scn_, table_key_.get_snapshot_version(), start_scn_))) {
+    if (OB_FAIL(update_tablet(saved_start_scn, saved_snapshot_version, saved_start_scn))) {
       LOG_WARN("clean up ddl sstable failed", K(ret), K(ls_id_), K(tablet_id_));
     }
   }