MDEV-7908: assertion in innobase_release_savepoint

Problem was that in XA prepared state we should still be able to
release a savepoint, but assertions were too strict.

mysql-test/suite/innodb/r/innodb-xa.result

+xa rollback 'xid2';
+ERROR XAE04: XAER_NOTA: Unknown XID
+drop table if exists t1;
+Warnings:
+Note	1051	Unknown table 'test.t1'
+create table t1(a int)engine=innodb;
+rollback;
+xa start 'xid2';
+insert into `t1` values (1);
+savepoint `sv1`;
+xa end 'xid2';
+start transaction;
+ERROR XAE07: XAER_RMFAIL: The command cannot be executed when global transaction is in the  IDLE state
+xa prepare 'xid2';
+release savepoint `sv1`;
+xa commit 'xid2';
+drop table t1;

mysql-test/suite/innodb/t/innodb-xa.test

+--source include/have_innodb.inc
+
+--disable_abort_on_error
+xa rollback 'xid2';
+drop table if exists t1;
+create table t1(a int)engine=innodb;
+rollback;
+xa start 'xid2';
+insert into `t1` values (1);
+savepoint `sv1`;
+xa end 'xid2';
+start transaction;
+xa prepare 'xid2';
+release savepoint `sv1`;
+xa commit 'xid2';
+drop table t1;
+

storage/innobase/handler/ha_innodb.cc

@@ -4116,7 +4116,10 @@ innobase_release_savepoint(
 	DBUG_ASSERT(hton == innodb_hton_ptr);
 
 	trx = check_trx_exists(thd);
-	trx_start_if_not_started(trx);
+
+	if (trx->state == TRX_STATE_NOT_STARTED) {
+		trx_start_if_not_started(trx);
+	}
 
 	/* TODO: use provided savepoint data area to store savepoint data */
 

storage/innobase/trx/trx0roll.cc

@@ -495,7 +495,7 @@ trx_release_savepoint_for_mysql(
 {
 	trx_named_savept_t*	savep;
 
-	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
+	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE) || trx_state_eq(trx, TRX_STATE_PREPARED));
 	ut_ad(trx->in_mysql_trx_list);
 
 	savep = trx_savepoint_find(trx, savepoint_name);

storage/xtradb/handler/ha_innodb.cc

@@ -4679,7 +4679,10 @@ innobase_release_savepoint(
 	DBUG_ASSERT(hton == innodb_hton_ptr);
 
 	trx = check_trx_exists(thd);
-	trx_start_if_not_started(trx);
+
+	if (trx->state == TRX_STATE_NOT_STARTED) {
+		trx_start_if_not_started(trx);
+	}
 
 	/* TODO: use provided savepoint data area to store savepoint data */
 

storage/xtradb/trx/trx0roll.cc

@@ -492,7 +492,7 @@ trx_release_savepoint_for_mysql(
 {
 	trx_named_savept_t*	savep;
 
-	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
+	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE) || trx_state_eq(trx, TRX_STATE_PREPARED));
 	ut_ad(trx->in_mysql_trx_list);
 
 	savep = trx_savepoint_find(trx, savepoint_name);