MDEV-20230: mariabackup --ftwrl-wait-timeout never times out on explicit

lock

--ftwrl-wait-timeout does not finish mariabackup execution when acquired
backup lock can't be grabbed for the certain amount of time, it just
waits for a long queries finishing before acquiring the lock to avoid
unnecessary locking.

This commit extends --ftwrl-wait-timeout so, that mariabackup execution
is finished if it waits for backup lock during certain amount of time.

extra/mariabackup/backup_mysql.cc

@@ -959,28 +959,33 @@ Function acquires either a backup tables lock, if supported
 by the server, or a global read lock (FLUSH TABLES WITH READ LOCK)
 otherwise.
 @returns true if lock acquired */
-bool
-lock_tables(MYSQL *connection)
+bool lock_tables(MYSQL *connection)
 {
-	if (have_lock_wait_timeout) {
+  if (have_lock_wait_timeout || opt_lock_wait_timeout)
+  {
+    char buf[FN_REFLEN];
     /* Set the maximum supported session value for
-		lock_wait_timeout to prevent unnecessary timeouts when the
-		global value is changed from the default */
-		xb_mysql_query(connection,
-			"SET SESSION lock_wait_timeout=31536000", false);
+    lock_wait_timeout if opt_lock_wait_timeout is not set to prevent
+    unnecessary timeouts when the global value is changed from the default */
+    snprintf(buf, sizeof(buf), "SET SESSION lock_wait_timeout=%u",
+             opt_lock_wait_timeout ? opt_lock_wait_timeout : 31536000);
+    xb_mysql_query(connection, buf, false);
   }
 
-	if (have_backup_locks) {
+  if (have_backup_locks)
+  {
     msg("Executing LOCK TABLES FOR BACKUP...");
     xb_mysql_query(connection, "LOCK TABLES FOR BACKUP", false);
-		return(true);
+    return (true);
   }
 
-	if (opt_lock_ddl_per_table) {
+  if (opt_lock_ddl_per_table)
+  {
     start_mdl_waiters_killer();
   }
 
-	if (!opt_lock_wait_timeout && !opt_kill_long_queries_timeout) {
+  if (!opt_lock_wait_timeout && !opt_kill_long_queries_timeout)
+  {
 
     /* We do first a FLUSH TABLES. If a long update is running, the
     FLUSH TABLES will wait but will not stall the whole mysqld, and
@@ -996,42 +1001,51 @@ lock_tables(MYSQL *connection)
 
     msg("Executing FLUSH NO_WRITE_TO_BINLOG TABLES...");
 
-		xb_mysql_query(connection,
-			       "FLUSH NO_WRITE_TO_BINLOG TABLES", false);
+    xb_mysql_query(connection, "FLUSH NO_WRITE_TO_BINLOG TABLES", false);
   }
 
-	if (opt_lock_wait_timeout) {
+  if (opt_lock_wait_timeout)
+  {
     if (!wait_for_no_updates(connection, opt_lock_wait_timeout,
-					 opt_lock_wait_threshold)) {
-			return(false);
+                             opt_lock_wait_threshold))
+    {
+      return (false);
     }
   }
 
   msg("Executing FLUSH TABLES WITH READ LOCK...");
 
-	if (opt_kill_long_queries_timeout) {
+  if (opt_kill_long_queries_timeout)
+  {
     start_query_killer();
   }
 
-	if (have_galera_enabled) {
-		xb_mysql_query(connection,
-				"SET SESSION wsrep_causal_reads=0", false);
+  if (have_galera_enabled)
+  {
+    xb_mysql_query(connection, "SET SESSION wsrep_causal_reads=0", false);
   }
 
-	xb_mysql_query(connection, "FLUSH TABLES WITH READ LOCK", false);
+  xb_mysql_query(connection, "FLUSH TABLES WITH READ LOCK", false, true);
+  /* Set the maximum supported session value for
+  lock_wait_timeout to prevent unnecessary timeouts when the
+  global value is changed from the default */
+  if (opt_lock_wait_timeout)
+    xb_mysql_query(connection, "SET SESSION lock_wait_timeout=31536000",
+                   false);
 
-	if (opt_lock_ddl_per_table) {
+  if (opt_lock_ddl_per_table)
+  {
     stop_mdl_waiters_killer();
   }
 
-	if (opt_kill_long_queries_timeout) {
+  if (opt_kill_long_queries_timeout)
+  {
     stop_query_killer();
   }
 
-	return(true);
+  return (true);
 }
 
-
 /*********************************************************************//**
 If backup locks are used, execute LOCK BINLOG FOR BACKUP provided that we are
 not in the --no-lock mode and the lock has not been acquired already.

mysql-test/suite/mariabackup/backup_lock_wait_timeout.result

+CREATE TABLE t(i INT) ENGINE INNODB;
+connect  con1,localhost,root,,;
+BEGIN;
+LOCK TABLES t WRITE;
+connection default;
+# xtrabackup backup
+connection con1;
+COMMIT;
+connection default;
+disconnect con1;
+DROP TABLE t;

mysql-test/suite/mariabackup/backup_lock_wait_timeout.test

+--source include/have_innodb.inc
+--source include/count_sessions.inc
+
+CREATE TABLE t(i INT) ENGINE INNODB;
+
+connect (con1,localhost,root,,);
+BEGIN;
+LOCK TABLES t WRITE;
+
+--connection default
+
+echo # xtrabackup backup;
+let $targetdir=$MYSQLTEST_VARDIR/tmp/backup;
+
+--disable_result_log
+--error 1
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --ftwrl-wait-timeout=1 --target-dir=$targetdir;
+--enable_result_log
+
+--connection con1
+COMMIT;
+
+--connection default
+--disconnect con1
+
+DROP TABLE t;
+rmdir $targetdir;
+--source include/wait_until_count_sessions.inc