Bug #50124 Rpl failure on DROP table with concurrent txn/non-txn

DML flow and SAVEPOINT

The problem was that replication could break if a transaction involving
both transactional and non-transactional tables was rolled back to a
savepoint. It broke if a concurrent connection tried to drop a
transactional table which was locked after the savepoint was set.
This DROP TABLE completed when ROLLBACK TO SAVEPOINT was executed as the
lock on the table was dropped by the transaction. When the slave later
tried to apply the binlog, it would fail as the table would already
have been dropped.

The reason for the problem is that transactions involving both
transactional and non-transactional tables are written fully to the
binlog during ROLLBACK TO SAVEPOINT. At the same time, metadata locks
acquired after a savepoint, were released during ROLLBACK TO SAVEPOINT.
This allowed a second connection to drop a table only used between
SAVEPOINT and ROLLBACK TO SAVEPOINT. Which caused the transaction binlog
to refer to a non-existing table when it was written during ROLLBACK
TO SAVEPOINT.

This patch fixes the problem by not releasing metadata locks when
ROLLBACK TO SAVEPOINT is executed if binlogging is enabled.

mysql-test/suite/rpl/r/rpl_savepoint.result

@@ -0,0 +1,32 @@
+stop slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+reset master;
+reset slave;
+drop table if exists t1,t2,t3,t4,t5,t6,t7,t8,t9;
+start slave;
+#
+# Bug#50124 Rpl failure on DROP table with concurrent txn/non-txn
+#           DML flow and SAVEPOINT
+#
+# Connection master
+DROP TABLE IF EXISTS tt, nt;
+CREATE TABLE tt (i INT) ENGINE = InnoDB;
+CREATE TABLE nt (i INT) ENGINE = MyISAM;
+FLUSH LOGS;
+START TRANSACTION;
+INSERT INTO nt VALUES (1);
+SAVEPOINT insert_statement;
+INSERT INTO tt VALUES (1);
+# Connection master1
+# Sending:
+DROP TABLE tt;
+# Connection master
+ROLLBACK TO SAVEPOINT insert_statement;
+Warnings:
+Warning	1196	Some non-transactional changed tables couldn't be rolled back
+COMMIT;
+# Connection master1
+# Reaping: DROP TABLE tt
+FLUSH LOGS;
+# Connection master
+DROP TABLE nt;

mysql-test/suite/rpl/t/rpl_savepoint.test

@@ -0,0 +1,47 @@
+--source include/master-slave.inc
+--source include/have_innodb.inc
+
+--echo #
+--echo # Bug#50124 Rpl failure on DROP table with concurrent txn/non-txn
+--echo #           DML flow and SAVEPOINT
+--echo #
+
+--echo # Connection master
+connection master;
+
+--disable_warnings
+DROP TABLE IF EXISTS tt, nt;
+--enable_warnings
+
+CREATE TABLE tt (i INT) ENGINE = InnoDB;
+CREATE TABLE nt (i INT) ENGINE = MyISAM;
+FLUSH LOGS;
+START TRANSACTION;
+INSERT INTO nt VALUES (1);
+SAVEPOINT insert_statement;
+INSERT INTO tt VALUES (1);
+
+--echo # Connection master1
+connection master1;
+--echo # Sending:
+--send DROP TABLE tt
+
+--echo # Connection master
+connection master;
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM information_schema.processlist
+  WHERE state = "Waiting for table" AND info = "DROP TABLE tt";
+--source include/wait_condition.inc
+ROLLBACK TO SAVEPOINT insert_statement;
+COMMIT;
+
+--echo # Connection master1
+connection master1;
+--echo # Reaping: DROP TABLE tt
+--reap
+FLUSH LOGS;
+
+--echo # Connection master
+connection master;
+DROP TABLE nt;
+--source include/master-slave-end.inc

sql/transaction.cc

@@ -419,9 +419,13 @@ bool trans_rollback_to_savepoint(THD *thd, LEX_STRING name)
   thd->transaction.savepoints= sv;
 
   /*
-    Release metadata locks that were acquired during this savepoint unit.
+    Release metadata locks that were acquired during this savepoint unit
+    unless binlogging is on. Releasing locks with binlogging on can break
+    replication as it allows other connections to drop these tables before
+    rollback to savepoint is written to the binlog.
   */
-  if (!res)
+  bool binlog_on= mysql_bin_log.is_open() && thd->variables.sql_log_bin;
+  if (!res && !binlog_on)
     thd->mdl_context.rollback_to_savepoint(sv->mdl_savepoint);
 
   DBUG_RETURN(test(res));