MDEV-13073. Fixed failing on BB sys_vars.rpl_semi_sync_master_enabled_basic. The issue forced to add up aan argument to THD::THD and THD::init to propagate skip of a mutex locking. The lock could not be released instead as this leads to clear deadlock; the test is received a piece for concurrent ack thread start/stop.bb-10.2-semisync

3 files changed, 21 insertions, 10 deletions

diff --git a/sql/semisync_master_ack_receiver.cc b/sql/semisync_master_ack_receiver.cc
index 7240d10b745..6cd02419e37 100644
--- a/sql/semisync_master_ack_receiver.cc
+++ b/sql/semisync_master_ack_receiver.cc
@@ -209,7 +209,8 @@ static void init_net(NET *net, unsigned char *buff, unsigned int buff_len)
 
 void Ack_receiver::run()
 {
-  THD *thd= new THD(next_thread_id());
+  // skip LOCK_global_system_variables due to the 3rd arg
+  THD *thd= new THD(next_thread_id(), false, true);
   NET net;
   unsigned char net_buff[REPLY_MESSAGE_MAX_LENGTH];
 
diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index afd0c375718..a97ad06c7f6 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -693,7 +693,7 @@ extern "C" void thd_kill_timeout(THD* thd)
 }
 
 
-THD::THD(my_thread_id id, bool is_wsrep_applier)
+THD::THD(my_thread_id id, bool is_wsrep_applier, bool skip_global_sys_var_lock)
   :Statement(&main_lex, &main_mem_root, STMT_CONVENTIONAL_EXECUTION,
              /* statement id */ 0),
    rli_fake(0), rgi_fake(0), rgi_slave(NULL),
@@ -880,7 +880,7 @@ THD::THD(my_thread_id id, bool is_wsrep_applier)
   /* Call to init() below requires fully initialized Open_tables_state. */
   reset_open_tables_state(this);
 
-  init();
+  init(skip_global_sys_var_lock);
 #if defined(ENABLED_PROFILING)
   profiling.set_thd(this);
 #endif
@@ -1237,10 +1237,11 @@ extern "C" my_thread_id next_thread_id_noinline()
   Init common variables that has to be reset on start and on change_user
 */
 
-void THD::init(void)
+void THD::init(bool skip_lock)
 {
   DBUG_ENTER("thd::init");
-  mysql_mutex_lock(&LOCK_global_system_variables);
+  if (!skip_lock)
+    mysql_mutex_lock(&LOCK_global_system_variables);
   plugin_thdvar_init(this);
   /*
     plugin_thd_var_init() sets variables= global_system_variables, which
@@ -1253,8 +1254,8 @@ void THD::init(void)
   ::strmake(variables.default_master_connection.str,
             global_system_variables.default_master_connection.str,
             variables.default_master_connection.length);
-
-  mysql_mutex_unlock(&LOCK_global_system_variables);
+  if (!skip_lock)
+    mysql_mutex_unlock(&LOCK_global_system_variables);
 
   user_time.val= start_time= start_time_sec_part= 0;
 
diff --git a/sql/sql_class.h b/sql/sql_class.h
index c0a6f5b0e62..b708b96053f 100644
--- a/sql/sql_class.h
+++ b/sql/sql_class.h
@@ -3098,11 +3098,20 @@ public:
   /* Debug Sync facility. See debug_sync.cc. */
   struct st_debug_sync_control *debug_sync_control;
 #endif /* defined(ENABLED_DEBUG_SYNC) */
-  THD(my_thread_id id, bool is_wsrep_applier= false);
+  /**
+    @param id                thread identifier
+    @param is_wsrep_applier  thread type
+    @param skip_lock         instruct whether @c LOCK_global_system_variables
+                             is already locked, to not acquire it then.
+  */
+  THD(my_thread_id id, bool is_wsrep_applier= false, bool skip_lock= false);
 
   ~THD();
-
-  void init(void);
+  /**
+    @param skip_lock         instruct whether @c LOCK_global_system_variables
+                             is already locked, to not acquire it then.
+  */
+  void init(bool skip_lock= false);
   /*
     Initialize memory roots necessary for query processing and (!)
     pre-allocate memory for it. We can't do that in THD constructor because