Index: Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/r/rpl_circular_event_detect.result
===================================================================
--- /dev/null
+++ Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/r/rpl_circular_event_detect.result
@@ -0,0 +1,21 @@
+[set up circular replication on two servers]
+include/rpl_init.inc [topology=1->2->1]
+
+[preparing data on server1]
+CREATE TABLE IF NOT EXISTS t (a VARCHAR(100)) ENGINE=InnoDB;
+[skip create table events on server1]
+call mtr.add_suppression("Detect dual master circular topological structure *");
+STOP SLAVE;
+STOP SLAVE;
+INSERT INTO t values('abc');
+SET GLOBAL SERVER_ID = 3;
+START SLAVE;
+START SLAVE;
+
+*** detect event with circle A->B->A  ***
+
+[clean up]
+SET GLOBAL SERVER_ID = 1;
+DROP TABLE IF EXISTS  t;
+include/rpl_reset.inc
+include/rpl_end.inc
Index: Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/t/rpl_circular_event_detect.test
===================================================================
--- /dev/null
+++ Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/t/rpl_circular_event_detect.test
@@ -0,0 +1,86 @@
+# ==== Purpose ====
+#
+# Confirm abnormal event with another server_id would be passed
+# among the circular replacted hosts, and it should be detected
+# with warning information.
+#
+#
+# ==== Related bugs and worklogs ====
+#
+
+# 1. setup environment: 
+#    server1(server_id=1)  <---(dual master)--> server2(server_id=2)
+# 2. create table t on server1, and it should be replicated to server2
+# 3. stop slave on server1
+# 4. insert one record on server1
+# 5. change server_id from 1 to 3 on server1
+# 6. start slave on server1
+# 7. expected record more than 1 on server1 (also warning of dual master for event)
+
+
+--source include/have_innodb.inc
+# Use wait_for_slave_to_(start|stop) for current connections
+let $keep_connection= 1;
+
+# Set up circular ring and new names for servers
+--echo [set up circular replication on two servers]
+--let $rpl_topology= 1->2->1
+--source include/rpl_init.inc
+--echo
+
+# Preparing data on server1.
+--echo [preparing data on server1]
+--connection server_1
+
+# make sure log_slave_updates is on
+#SET session log_slave_updates=on;
+
+#CREATE TABLE IF NOT EXISTS t (a INT NOT NULL AUTO_INCREMENT, b VARCHAR(100), PRIMARY KEY(a)) ENGINE=InnoDB;
+CREATE TABLE IF NOT EXISTS t (a VARCHAR(100)) ENGINE=InnoDB;
+
+--echo [skip create table events on server1]
+#CHANGE MASTER TO master_log_pos=276;
+
+call mtr.add_suppression("Detect dual master circular topological structure *");
+
+--real_sleep 1
+STOP SLAVE;
+
+--connection server_2
+STOP SLAVE;
+
+--connection server_1
+INSERT INTO t values('abc');
+
+SET GLOBAL SERVER_ID = 3;
+START SLAVE;
+
+--connection server_2
+START SLAVE;
+
+
+#--real_sleep 3
+
+--connection server_1
+let $wait_condition= SELECT COUNT(*) > 10 FROM t;
+--source include/wait_condition.inc
+#select * from t;
+
+--connection server_2
+#select * from t;
+
+--echo
+--echo *** detect event with circle A->B->A  ***
+--echo
+
+--disable_warnings
+
+# Clean up environment
+--echo [clean up]
+
+--connection server_1
+SET GLOBAL SERVER_ID = 1;
+DROP TABLE IF EXISTS  t;
+
+--source include/rpl_reset.inc
+--source include/rpl_end.inc
Index: Percona-Server-5.5.18-rel23.0/sql/mysqld.cc
===================================================================
--- Percona-Server-5.5.18-rel23.0.orig/sql/mysqld.cc
+++ Percona-Server-5.5.18-rel23.0/sql/mysqld.cc
@@ -374,6 +374,10 @@ my_bool locked_in_memory;
 bool opt_using_transactions;
 bool volatile abort_loop;
 bool volatile shutdown_in_progress;
+LIST *slave_id_list=NULL;
+int set_warning;
+pthread_mutex_t slave_id_list_mutex;
+
 /*
   True if the bootstrap thread is running. Protected by LOCK_thread_count,
   just like thread_count.
@@ -1550,6 +1554,7 @@ void clean_up(bool print_message)
   mysql_cond_broadcast(&COND_thread_count);
   mysql_mutex_unlock(&LOCK_thread_count);
   sys_var_end();
+  list_free(slave_id_list, 1);
 
   /*
     The following lines may never be executed as the main thread may have
@@ -1583,6 +1588,7 @@ static void wait_for_signal_thread_to_en
 
 static void clean_up_mutexes()
 {
+  (void)pthread_mutex_destroy(&slave_id_list_mutex);
   mysql_rwlock_destroy(&LOCK_grant);
   mysql_mutex_destroy(&LOCK_thread_count);
   mysql_mutex_destroy(&LOCK_status);
@@ -3632,6 +3638,7 @@ You should consider changing lower_case_
 
 static int init_thread_environment()
 {
+  pthread_mutex_init(&slave_id_list_mutex, MY_MUTEX_INIT_FAST);
   mysql_mutex_init(key_LOCK_thread_count, &LOCK_thread_count, MY_MUTEX_INIT_FAST);
   mysql_mutex_init(key_LOCK_status, &LOCK_status, MY_MUTEX_INIT_FAST);
   mysql_mutex_init(key_LOCK_delayed_insert,
Index: Percona-Server-5.5.18-rel23.0/sql/slave.cc
===================================================================
--- Percona-Server-5.5.18-rel23.0.orig/sql/slave.cc
+++ Percona-Server-5.5.18-rel23.0/sql/slave.cc
@@ -3848,6 +3848,35 @@ static int queue_old_event(Master_info *
   }
 }
 
+/* loop server's slave id list to check whether exists the server_id.
+ * return index if found, else return -1
+ */
+static int find_in_slave_id_list(uint32 server_id)
+{
+    if (!slave_id_list)
+        return -1;
+
+    int index=0;
+    int found=0;
+    
+    pthread_mutex_lock(&slave_id_list_mutex);
+    LIST *list = slave_id_list;
+    for (index=0; list ; list=list->next, index++) {
+        if (*(uint32*)list->data == server_id) {
+            found = 1;
+            break;
+        }
+    }
+
+    pthread_mutex_unlock(&slave_id_list_mutex);
+
+    if (found)
+        return index;
+    else
+        return -1;
+}
+
+
 /*
   queue_event()
 
@@ -4060,6 +4089,22 @@ static int queue_event(Master_info* mi,c
   }
   else
   {
+      if (s_id != ::server_id &&
+          -1 == find_in_slave_id_list(s_id) &&
+          -1 != find_in_slave_id_list(mi->master_id)) {
+          /* if replicated event's server_id is neither the same with current 
+           * instance's id, nor current instance's id, a warning should be given
+           * for dual mastser topological structure.
+           */
+          if (set_warning) {
+            sql_print_warning(
+                      "Detect dual master circular topological structure: "
+                      "event_sid=%ld, server id=%ld, master(slave) id=%ld ",
+                      s_id, ::server_id, mi->master_id);
+              set_warning = 0;
+          }
+      }
+
     /* write the event to the relay log */
     if (likely(!(rli->relay_log.appendv(buf,event_len,0))))
     {
Index: Percona-Server-5.5.18-rel23.0/sql/sql_parse.cc
===================================================================
--- Percona-Server-5.5.18-rel23.0.orig/sql/sql_parse.cc
+++ Percona-Server-5.5.18-rel23.0/sql/sql_parse.cc
@@ -1235,10 +1235,12 @@ bool dispatch_command(enum enum_server_c
 	kill_zombie_dump_threads(slave_server_id);
       thd->server_id = slave_server_id;
 
+      update_slave_id_list(slave_server_id, OP_INSERT);
       general_log_print(thd, command, "Log: '%s'  Pos: %ld", packet+10,
                       (long) pos);
       mysql_binlog_send(thd, thd->strdup(packet + 10), (my_off_t) pos, flags);
       unregister_slave(thd,1,1);
+      update_slave_id_list(slave_server_id, OP_DELETE);
       /*  fake COM_QUIT -- if we get here, the thread needs to terminate */
       error = TRUE;
       break;
Index: Percona-Server-5.5.18-rel23.0/sql/sql_repl.cc
===================================================================
--- Percona-Server-5.5.18-rel23.0.orig/sql/sql_repl.cc
+++ Percona-Server-5.5.18-rel23.0/sql/sql_repl.cc
@@ -429,6 +429,37 @@ static int send_heartbeat_event(NET* net
   DBUG_RETURN(0);
 }
 
+/* update global slave id list when binlog dump thread is started or exited */
+void update_slave_id_list(uint32 server_id, list_op op)
+{
+  pthread_mutex_lock(&slave_id_list_mutex);
+  LIST *list = slave_id_list;
+  //fprintf(stderr, "op=%d id=%d len=%d\n", op, server_id, list_length(list));
+
+  set_warning = 1;
+
+  if (op == OP_INSERT) {
+      LIST *element = (LIST*)my_malloc(sizeof(LIST*), MYF(MY_FAE));
+      element->data = (void*)my_malloc(sizeof(void*), MYF(MY_FAE|MY_ZEROFILL));
+      memcpy(element->data, &server_id, sizeof(uint32));
+      slave_id_list = list_add(slave_id_list, element);
+  } else if (op == OP_DELETE) {
+      while (list) {
+            if (*(uint32*)list->data == server_id) {
+                //fprintf(stderr, "\t found it !\n");
+                slave_id_list = list_delete(slave_id_list, list);
+                my_free(list->data);
+                my_free(list);
+                break;
+            }
+            list=list->next;
+      }
+  }
+
+  pthread_mutex_unlock(&slave_id_list_mutex);
+}
+
+
 /*
   TODO: Clean up loop to only have one call to send_file()
 */
Index: Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/t/rpl_circular_event_detect.cnf
===================================================================
--- /dev/null
+++ Percona-Server-5.5.18-rel23.0/mysql-test/suite/rpl/t/rpl_circular_event_detect.cnf
@@ -0,0 +1,10 @@
+!include ../my.cnf
+
+[mysqld.1]
+log-slave-updates
+innodb
+
+[mysqld.2]
+log-slave-updates
+innodb
+
Index: Percona-Server-5.5.18-rel23.0/sql/sql_repl.h
===================================================================
--- Percona-Server-5.5.18-rel23.0.orig/sql/sql_repl.h
+++ Percona-Server-5.5.18-rel23.0/sql/sql_repl.h
@@ -32,6 +32,14 @@ typedef struct st_slave_info
   THD* thd;
 } SLAVE_INFO;
 
+typedef enum en_list_op { OP_INSERT=0, OP_DELETE } list_op;
+
+extern LIST *slave_id_list;
+extern int set_warning;
+extern pthread_mutex_t slave_id_list_mutex;
+
+void update_slave_id_list(uint32 server_id, list_op op);
+
 extern my_bool opt_show_slave_auth_info;
 extern char *master_host, *master_info_file;
 extern bool server_id_supplied;