Merge fix for BUG51342 to 5.0-bugteam.

mysql-test/r/xa.result

@@ -74,4 +74,21 @@ ERROR XA102: XA_RBDEADLOCK: Transaction branch was rolled back: deadlock was det
 xa rollback 'a','c';
 xa start 'a','c';
 drop table t1;
+#
+# BUG#51342 - more xid crashing
+#
+CREATE TABLE t1(a INT) ENGINE=InnoDB;
+XA START 'x';
+SET SESSION autocommit=0;
+INSERT INTO t1 VALUES(1);
+SET SESSION autocommit=1;
+ERROR XAE07: XAER_RMFAIL: The command cannot be executed when global transaction is in the  ACTIVE state
+SELECT @@autocommit;
+@@autocommit
+0
+INSERT INTO t1 VALUES(1);
+XA END 'x';
+XA COMMIT 'x' ONE PHASE;
+DROP TABLE t1;
+SET SESSION autocommit=DEFAULT;
 End of 5.0 tests

mysql-test/t/xa.test

@@ -122,6 +122,22 @@ xa start 'a','c';
 --connection default
 drop table t1;
 
+--echo #
+--echo # BUG#51342 - more xid crashing
+--echo #
+CREATE TABLE t1(a INT) ENGINE=InnoDB;
+XA START 'x';
+SET SESSION autocommit=0;
+INSERT INTO t1 VALUES(1);
+--error ER_XAER_RMFAIL
+SET SESSION autocommit=1;
+SELECT @@autocommit;
+INSERT INTO t1 VALUES(1);
+XA END 'x';
+XA COMMIT 'x' ONE PHASE;
+DROP TABLE t1;
+SET SESSION autocommit=DEFAULT;
+
 --echo End of 5.0 tests
 
 # Wait till all disconnects are completed

sql/set_var.cc

@@ -3065,6 +3065,13 @@ static bool set_option_autocommit(THD *thd, set_var *var)
     if ((org_options & OPTION_NOT_AUTOCOMMIT))
     {
       /* We changed to auto_commit mode */
+      if (thd->transaction.xid_state.xa_state != XA_NOTR)
+      {
+        thd->options= org_options;
+        my_error(ER_XAER_RMFAIL, MYF(0),
+                 xa_state_names[thd->transaction.xid_state.xa_state]);
+        return 1;
+      }
       thd->options&= ~OPTION_BEGIN;
       thd->transaction.all.modified_non_trans_table= FALSE;
       thd->server_status|= SERVER_STATUS_AUTOCOMMIT;