MDEV-26391 BF abortable mariabackup execution

This commit changes backup execution (namely the block ddl phase),
so that node is not paused from cluster. Instead, the following
backup execution is declared as vulnerable for possible cluster
level conflicts, especially with DDL statement applying.
With this, the mariabackup execution may be aborted, if DDL
statements happen during backup execution. This abortable
backup execution is optional feature and may be
enabled/disabled by wsrep_mode: BF_ABORT_MARIABACKUP.
Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

mysql-test/suite/galera/r/galera_var_wsrep_mode.result

@@ -20,8 +20,8 @@ SET GLOBAL wsrep_mode='A';
 ERROR 42000: Variable 'wsrep_mode' can't be set to the value of 'A'
 SET GLOBAL wsrep_mode=NULL;
 ERROR 42000: Variable 'wsrep_mode' can't be set to the value of 'NULL'
-SET GLOBAL wsrep_mode=64;
-ERROR 42000: Variable 'wsrep_mode' can't be set to the value of '64'
+SET GLOBAL wsrep_mode=128;
+ERROR 42000: Variable 'wsrep_mode' can't be set to the value of '128'
 SET GLOBAL wsrep_mode=REQUIRED_PRIMARY_KEY,REPLICATE_MYISAM;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1
 SET GLOBAL wsrep_mode=1;

mysql-test/suite/galera/t/galera_var_wsrep_mode.test

@@ -22,7 +22,7 @@ SET GLOBAL wsrep_mode='A';
 --error ER_WRONG_VALUE_FOR_VAR
 SET GLOBAL wsrep_mode=NULL;
 --error ER_WRONG_VALUE_FOR_VAR
-SET GLOBAL wsrep_mode=64;
+SET GLOBAL wsrep_mode=128;
 --error ER_PARSE_ERROR
 SET GLOBAL wsrep_mode=REQUIRED_PRIMARY_KEY,REPLICATE_MYISAM;
 #

sql/backup.cc

@@ -36,6 +36,7 @@
 #include <my_sys.h>
 #include <strfunc.h>                           // strconvert()
 #include "wsrep_mysqld.h"
+#include "debug_sync.h"
 #ifdef WITH_WSREP
 #include "wsrep_server_state.h"
 #endif /* WITH_WSREP */
@@ -295,7 +296,7 @@ static bool backup_block_ddl(THD *thd)
     We desync the node for BACKUP STAGE because applier threads
     bypass backup MDL locks (see MDL_lock::can_grant_lock)
   */
-  if (WSREP_NNULL(thd))
+  if (WSREP_NNULL(thd) && !wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP))
   {
     Wsrep_server_state &server_state= Wsrep_server_state::instance();
     if (server_state.desync_and_pause().is_undefined()) {
@@ -341,6 +342,18 @@ static bool backup_block_ddl(THD *thd)
   /* There can't be anything more that needs to be logged to ddl log */
   THD_STAGE_INFO(thd, org_stage);
   stop_ddl_logging();
+#ifdef WITH_WSREP
+  // Allow tests to block the applier thread using the DBUG facilities
+  DBUG_EXECUTE_IF("sync.wsrep_after_mdl_block_ddl",
+                  {
+                   const char act[]=
+                     "now "
+                     "signal signal.wsrep_apply_toi";
+                   DBUG_ASSERT(!debug_sync_set_action(thd,
+                                                      STRING_WITH_LEN(act)));
+                  };);
+#endif /* WITH_WSREP */
+
   DBUG_RETURN(0);
 err:
   THD_STAGE_INFO(thd, org_stage);
@@ -400,7 +413,8 @@ bool backup_end(THD *thd)
     thd->current_backup_stage= BACKUP_FINISHED;
     thd->mdl_context.release_lock(old_ticket);
 #ifdef WITH_WSREP
-    if (WSREP_NNULL(thd) && thd->wsrep_desynced_backup_stage)
+    if (WSREP_NNULL(thd) && thd->wsrep_desynced_backup_stage &&
+	!wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP))
     {
       Wsrep_server_state &server_state= Wsrep_server_state::instance();
       THD_STAGE_INFO(thd, stage_waiting_flow);

sql/mdl.cc

@@ -1750,7 +1750,8 @@ MDL_lock::can_grant_lock(enum_mdl_type type_arg,
     We should get rid of this code and forbid FTWRL/BACKUP statements
     when wsrep is active.
   */
-  if ((wsrep_thd_is_toi(requestor_ctx->get_thd()) ||
+  if (!wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP) &&
+      (wsrep_thd_is_toi(requestor_ctx->get_thd()) ||
        wsrep_thd_is_applying(requestor_ctx->get_thd())) &&
       key.mdl_namespace() == MDL_key::BACKUP)
   {

sql/service_wsrep.cc

@@ -241,7 +241,7 @@ extern "C" my_bool wsrep_thd_bf_abort(THD *bf_thd, THD *victim_thd,
     victim_thd->awake_no_mutex(KILL_QUERY);
     mysql_mutex_unlock(&victim_thd->LOCK_thd_data);
   } else {
-    WSREP_DEBUG("wsrep_thd_bf_abort skipped awake");
+    WSREP_DEBUG("wsrep_thd_bf_abort skipped awake, signal %d", signal);
   }
   return ret;
 }
@@ -277,7 +277,6 @@ extern "C" my_bool wsrep_thd_is_aborting(const MYSQL_THD thd)
       return (cs.state() == wsrep::client_state::s_exec ||
               cs.state() == wsrep::client_state::s_result);
     case wsrep::transaction::s_aborting:
-    case wsrep::transaction::s_aborted:
       return true;
     default:
       return false;

sql/sys_vars.cc

@@ -6028,6 +6028,7 @@ static const char *wsrep_mode_names[]=
   "REPLICATE_MYISAM",
   "REPLICATE_ARIA",
   "DISALLOW_LOCAL_GTID",
+  "BF_ABORT_MARIABACKUP",
   NullS
 };
 static Sys_var_set Sys_wsrep_mode(

sql/wsrep_mysqld.cc

@@ -3078,6 +3078,11 @@ void wsrep_handle_mdl_conflict(MDL_context *requestor_ctx,
       THD_STAGE_INFO(request_thd, stage_waiting_ddl);
       ticket->wsrep_report(wsrep_debug);
       mysql_mutex_unlock(&granted_thd->LOCK_thd_data);
+      if (granted_thd->current_backup_stage != BACKUP_FINISHED &&
+	  wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP))
+      {
+	wsrep_abort_thd(request_thd, granted_thd, 1);
+      }
     }
     else if (request_thd->lex->sql_command == SQLCOM_DROP_TABLE)
     {

sql/wsrep_mysqld.h

@@ -128,7 +128,8 @@ enum enum_wsrep_mode {
   WSREP_MODE_REQUIRED_PRIMARY_KEY= (1ULL << 2),
   WSREP_MODE_REPLICATE_MYISAM= (1ULL << 3),
   WSREP_MODE_REPLICATE_ARIA= (1ULL << 4),
-  WSREP_MODE_DISALLOW_LOCAL_GTID= (1ULL << 5)
+  WSREP_MODE_DISALLOW_LOCAL_GTID= (1ULL << 5),
+  WSREP_MODE_BF_MARIABACKUP= (1ULL << 6)
 };
 
 // Streaming Replication

sql/wsrep_thd.cc

@@ -375,6 +375,14 @@ bool wsrep_bf_abort(THD* bf_thd, THD* victim_thd)
        have acquired MDL locks (due to DDL execution), and this has caused BF conflict.
        such case does not require aborting in wsrep or replication provider state.
     */
+    if (victim_thd->current_backup_stage != BACKUP_FINISHED &&
+        wsrep_check_mode(WSREP_MODE_BF_MARIABACKUP))
+    {
+      WSREP_DEBUG("killing connection for non wsrep session");
+      mysql_mutex_lock(&victim_thd->LOCK_thd_data);
+      victim_thd->awake_no_mutex(KILL_CONNECTION);
+      mysql_mutex_unlock(&victim_thd->LOCK_thd_data);
+    }
     return false;
   }