MDEV-7123 : MariaDB 10.0.14 Galera node shutdown with signal 11

wsrep-patch uses same connection name for constructing Master_info
objects. As a result all existing wsrep Master_info objects refer
to same rpl_filter object. This could lead to race when multiple
threads try to delete/destruct Master_info object, as they would
all try to delete the same relay_log object.

Fixed by adding a check in Master_info's destructor to not free
the "wsrep" rpl_filter, so that its reused by current & subsequent
wsrep threads and later reclaimed by free_all_rpl_filters() during
server shutdown.

sql/keycaches.cc

@@ -223,6 +223,7 @@ Rpl_filter *get_or_create_rpl_filter(const char *name, uint length)
 void free_rpl_filter(const char *name, Rpl_filter *filter)
 {
   delete filter;
+  filter= 0;
 }
 
 void free_all_rpl_filters()

sql/rpl_mi.cc

@@ -89,6 +89,13 @@ Master_info::Master_info(LEX_STRING *connection_name_arg,
 
 Master_info::~Master_info()
 {
+#ifdef WITH_WSREP
+  /*
+    Do not free "wsrep" rpl_filter. It will eventually be freed by
+    free_all_rpl_filters() when server terminates.
+  */
+  if (strncmp(connection_name.str, STRING_WITH_LEN("wsrep")))
+#endif
   rpl_filters.delete_element(connection_name.str, connection_name.length,
                              (void (*)(const char*, uchar*)) free_rpl_filter);
   my_free(connection_name.str);

sql/wsrep_thd.cc

@@ -99,12 +99,27 @@ static rpl_group_info* wsrep_relay_group_init(const char* log_fname)
     rli->relay_log.description_event_for_exec=
       new Format_description_log_event(4);
   }
-  static LEX_STRING dbname= { C_STRING_WITH_LEN("mysql") };
 
-  rli->mi = new Master_info( &dbname,  false);
+  static LEX_STRING connection_name= { C_STRING_WITH_LEN("wsrep") };
 
-  rli->mi->rpl_filter = new Rpl_filter;
-  copy_filter_setting(rli->mi->rpl_filter, get_or_create_rpl_filter("", 0));
+  /*
+    Master_info's constructor initializes rpl_filter by either an already
+    constructed Rpl_filter object from global 'rpl_filters' list if the
+    specified connection name is same, or it constructs a new Rpl_filter
+    object and adds it to rpl_filters. This object is later destructed by
+    Mater_info's destructor by looking it up based on connection name in
+    rpl_filters list.
+
+    However, since all Master_info objects created here would share same
+    connection name ("wsrep"), destruction of any of the existing Master_info
+    objects (in wsrep_return_from_bf_mode()) would free rpl_filter referenced
+    by any/all existing Master_info objects.
+
+    In order to avoid that, we have added a check in Master_info's destructor
+    to not free the "wsrep" rpl_filter. It will eventually be freed by
+    free_all_rpl_filters() when server terminates.
+  */
+  rli->mi = new Master_info(&connection_name, false);
 
   rli->sql_driver_thd= current_thd;
 
@@ -155,7 +170,6 @@ static void wsrep_return_from_bf_mode(THD *thd, struct wsrep_thd_shadow* shadow)
   thd->reset_db(shadow->db, shadow->db_length);
 
   delete thd->system_thread_info.rpl_sql_info;
-  delete thd->wsrep_rgi->rli->mi->rpl_filter;
   delete thd->wsrep_rgi->rli->mi;
   delete thd->wsrep_rgi->rli;
   delete thd->wsrep_rgi;