Fix for bug #51263 "Deadlock between transactional

SELECT and ALTER TABLE ...  REBUILD PARTITION".

ALTER TABLE on InnoDB table (including partitioned tables)
acquired exclusive locks on rows of table being altered.
In cases when there was concurrent transaction which did
locking reads from this table this sometimes led to a
deadlock which was not detected by MDL subsystem nor by
InnoDB engine (and was reported only after exceeding
innodb_lock_wait_timeout).

This problem stemmed from the fact that ALTER TABLE acquired
TL_WRITE_ALLOW_READ lock on table being altered. This lock
was interpreted as a write lock and thus for table being
altered handler::external_lock() method was called with
F_WRLCK as an argument. As result InnoDB engine treated
ALTER TABLE as an operation which is going to change data
and acquired LOCK_X locks on rows being read from old
version of table.

In case when there was a transaction which already acquired
SR metadata lock on table and some LOCK_S locks on its rows
(e.g. by using it in subquery of DML statement) concurrent
ALTER TABLE was blocked at the moment when it tried to
acquire LOCK_X lock before reading one of these rows.
The transaction's attempt to acquire SW metadata lock on
table being altered led to deadlock, since it had to wait
for ALTER TABLE to release SNW lock. This deadlock was not
detected and got resolved only after timeout expiring
because waiting were happening in two different subsystems.

Similar deadlocks could have occured in other situations.
This patch tries to solve the problem by changing ALTER TABLE
implementation to use TL_READ_NO_INSERT lock instead of
TL_WRITE_ALLOW_READ. After this step handler::external_lock()
is called with F_RDLCK as an argument and InnoDB engine
correctly interprets ALTER TABLE as operation which only
reads data from original version of table. Thanks to this
ALTER TABLE acquires only LOCK_S locks on rows it reads.
This, in its turn, causes inter-subsystem deadlocks to go
away, as all potential lock conflicts and thus deadlocks will
be limited to metadata locking subsystem:

- When ALTER TABLE reads rows from table being altered it
  can't encounter any locks which conflict with LOCK_S row
  locks. There should be no concurrent transactions holding
  LOCK_X row locks. Such a transaction should have been
  acquired SW metadata lock on table first which would have
  conflicted with ALTER's SNW lock.
- Vice versa, when DML which runs concurrently with ALTER
  TABLE tries to lock row it should be requesting only LOCK_S
  lock which is compatible with locks acquired by ALTER,
  as otherwise such DML must own an SW metadata lock on table
  which would be incompatible with ALTER's SNW lock.

mysql-test/r/innodb_mysql_lock2.result

@@ -562,3 +562,68 @@ drop view v1, v2;
 drop procedure p1;
 drop procedure p2;
 drop table t1, t2, t3, t4, t5;
+#
+# Test for bug#51263 "Deadlock between transactional SELECT
+# and ALTER TABLE ... REBUILD PARTITION".
+#
+drop table if exists t1, t2;
+create table t1 (i int auto_increment not null primary key) engine=innodb;
+create table t2 (i int) engine=innodb;
+insert into t1 values (1), (2), (3), (4), (5);
+begin;
+# Acquire SR metadata lock on t1 and LOCK_S row-locks on its rows.
+insert into t2 select count(*) from t1;
+# Switching to connection 'con1'.
+# Sending:
+alter table t1 add column j int;
+# Switching to connection 'default'.
+# Wait until ALTER is blocked because it tries to upgrade SNW
+# metadata lock to X lock.
+# It should not be blocked during copying data to new version of
+# table as it acquires LOCK_S locks on rows of old version, which
+# are compatible with locks acquired by connection 'con1'.
+# The below statement will deadlock because it will try to acquire
+# SW lock on t1, which will conflict with ALTER's SNW lock. And
+# ALTER will be waiting for this connection to release its SR lock.
+# This deadlock should be detected by an MDL subsystem and this
+# statement should be aborted with an appropriate error.
+insert into t1 values (6);
+ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
+# Unblock ALTER TABLE.
+commit;
+# Switching to connection 'con1'.
+# Reaping ALTER TABLE.
+# Switching to connection 'default'.
+#
+# Now test for scenario in which bug was reported originally.
+#
+drop tables t1, t2;
+create table t1 (i int auto_increment not null primary key) engine=innodb
+partition by hash (i) partitions 4;
+create table t2 (i int) engine=innodb;
+insert into t1 values (1), (2), (3), (4), (5);
+begin;
+# Acquire SR metadata lock on t1.
+select * from t1;
+i
+1
+2
+3
+4
+5
+# Switching to connection 'con1'.
+# Sending:
+alter table t1 rebuild partition p0;
+# Switching to connection 'default'.
+# Wait until ALTER is blocked because of active SR lock.
+# The below statement should succeed as transaction
+# has SR metadata lock on t1 and only going to read
+# rows from it.
+insert into t2 select count(*) from t1;
+# Unblock ALTER TABLE.
+commit;
+# Switching to connection 'con1'.
+# Reaping ALTER TABLE.
+# Switching to connection 'default'.
+# Clean-up.
+drop tables t1, t2;

mysql-test/suite/rpl_ndb/r/rpl_ndb_binlog_format_errors.result

@@ -43,9 +43,9 @@ SELECT * FROM t /* Should be empty */;
 a
 * Modify both row-only and stmt-only table
 CREATE TRIGGER trig_2 AFTER INSERT ON t_stmt FOR EACH ROW BEGIN INSERT INTO t_row VALUES(1); END;
-ERROR HY000: Cannot execute statement: impossible to write to binary log since BINLOG_FORMAT = ROW and at least one table uses a storage engine limited to statement-based logging.
 INSERT INTO t_stmt VALUES (1);
-ERROR HY000: Cannot execute statement: impossible to write to binary log since BINLOG_FORMAT = ROW and at least one table uses a storage engine limited to statement-based logging.
+ERROR HY000: Cannot execute statement: impossible to write to binary log since both row-incapable engines and statement-incapable engines are involved.
+DROP trigger trig_2;
 SELECT * FROM t_stmt /* should be empty */;
 a
 * Stmt-only table and binlog_format=row

mysql-test/suite/rpl_ndb/t/rpl_ndb_binlog_format_errors.test

@@ -97,10 +97,10 @@ SELECT * FROM t_self_logging /* Should be empty */;
 SELECT * FROM t /* Should be empty */;
 
 --echo * Modify both row-only and stmt-only table
---error ER_BINLOG_ROW_MODE_AND_STMT_ENGINE
 --eval CREATE TRIGGER trig_2 AFTER INSERT ON t_stmt FOR EACH ROW BEGIN INSERT INTO t_row VALUES(1); END
---error ER_BINLOG_ROW_MODE_AND_STMT_ENGINE
+--error ER_BINLOG_ROW_ENGINE_AND_STMT_ENGINE
 INSERT INTO t_stmt VALUES (1);
+DROP trigger trig_2;
 SELECT * FROM t_stmt /* should be empty */;
 
 --echo * Stmt-only table and binlog_format=row

mysql-test/t/innodb_mysql_lock2.test

@@ -3,7 +3,12 @@
 # This test requires statement/mixed mode binary logging.
 # Row-based mode puts weaker serializability requirements
 # so weaker locks are acquired for it.
+# Also in ROW mode LOCK_S row locks won't be acquired for DML
+# and test for bug#51263 won't trigger execution path on which
+# this bug was encountered.
 --source include/have_binlog_format_mixed_or_statement.inc
+# Original test case for bug#51263 needs partitioning.
+--source include/have_partition.inc
 # Save the initial number of concurrent sessions.
 --source include/count_sessions.inc
 
@@ -760,6 +765,104 @@ drop procedure p2;
 drop table t1, t2, t3, t4, t5;
 disconnect con1;
 
+
+--echo #
+--echo # Test for bug#51263 "Deadlock between transactional SELECT
+--echo # and ALTER TABLE ... REBUILD PARTITION".
+--echo #
+connect (con1,localhost,root,,test,,);
+connection default;
+--disable_warnings
+drop table if exists t1, t2;
+--enable_warnings
+create table t1 (i int auto_increment not null primary key) engine=innodb;
+create table t2 (i int) engine=innodb;
+insert into t1 values (1), (2), (3), (4), (5);
+
+begin;
+--echo # Acquire SR metadata lock on t1 and LOCK_S row-locks on its rows.
+insert into t2 select count(*) from t1;
+
+--echo # Switching to connection 'con1'.
+connection con1;
+--echo # Sending:
+--send alter table t1 add column j int
+
+--echo # Switching to connection 'default'.
+connection default;
+--echo # Wait until ALTER is blocked because it tries to upgrade SNW
+--echo # metadata lock to X lock.
+--echo # It should not be blocked during copying data to new version of
+--echo # table as it acquires LOCK_S locks on rows of old version, which
+--echo # are compatible with locks acquired by connection 'con1'.
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist where state =
+    "Waiting for table" and info = "alter table t1 add column j int";
+--source include/wait_condition.inc
+
+--echo # The below statement will deadlock because it will try to acquire
+--echo # SW lock on t1, which will conflict with ALTER's SNW lock. And
+--echo # ALTER will be waiting for this connection to release its SR lock.
+--echo # This deadlock should be detected by an MDL subsystem and this
+--echo # statement should be aborted with an appropriate error.
+--error ER_LOCK_DEADLOCK
+insert into t1 values (6);
+--echo # Unblock ALTER TABLE.
+commit;
+
+--echo # Switching to connection 'con1'.
+connection con1;
+--echo # Reaping ALTER TABLE.
+--reap
+
+--echo # Switching to connection 'default'.
+connection default;
+
+--echo #
+--echo # Now test for scenario in which bug was reported originally.
+--echo #
+drop tables t1, t2;
+create table t1 (i int auto_increment not null primary key) engine=innodb
+  partition by hash (i) partitions 4;
+create table t2 (i int) engine=innodb;
+insert into t1 values (1), (2), (3), (4), (5);
+
+begin;
+--echo # Acquire SR metadata lock on t1.
+select * from t1;
+
+--echo # Switching to connection 'con1'.
+connection con1;
+--echo # Sending:
+--send alter table t1 rebuild partition p0
+
+--echo # Switching to connection 'default'.
+connection default;
+--echo # Wait until ALTER is blocked because of active SR lock.
+let $wait_condition=
+  select count(*) = 1 from information_schema.processlist
+  where state = "Waiting for table" and info = "alter table t1 rebuild partition p0";
+--source include/wait_condition.inc
+
+--echo # The below statement should succeed as transaction
+--echo # has SR metadata lock on t1 and only going to read
+--echo # rows from it.
+insert into t2 select count(*) from t1;
+--echo # Unblock ALTER TABLE.
+commit;
+
+--echo # Switching to connection 'con1'.
+connection con1;
+--echo # Reaping ALTER TABLE.
+--reap
+
+--echo # Switching to connection 'default'.
+connection default;
+disconnect con1;
+--echo # Clean-up.
+drop tables t1, t2;
+
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc

sql/ha_partition.cc

@@ -1302,7 +1302,7 @@ int ha_partition::prepare_new_partition(TABLE *tbl,
     assumes that external_lock() is last call that may fail here.
     Otherwise see description for cleanup_new_partition().
   */
-  if ((error= file->ha_external_lock(ha_thd(), m_lock_type)))
+  if ((error= file->ha_external_lock(ha_thd(), F_WRLCK)))
     goto error_external_lock;
   DBUG_PRINT("info", ("partition %s external locked", part_name));
 

sql/lock.cc

@@ -415,7 +415,7 @@ void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock)
   THR_LOCK_DATA **lock=sql_lock->locks;
   for (i=found=0 ; i < sql_lock->lock_count ; i++)
   {
-    if (sql_lock->locks[i]->type >= TL_WRITE_ALLOW_READ)
+    if (sql_lock->locks[i]->type > TL_WRITE_ALLOW_WRITE)
     {
       swap_variables(THR_LOCK_DATA *, *lock, sql_lock->locks[i]);
       lock++;
@@ -435,7 +435,7 @@ void mysql_unlock_read_tables(THD *thd, MYSQL_LOCK *sql_lock)
   for (i=found=0 ; i < sql_lock->table_count ; i++)
   {
     DBUG_ASSERT(sql_lock->table[i]->lock_position == i);
-    if ((uint) sql_lock->table[i]->reginfo.lock_type >= TL_WRITE_ALLOW_READ)
+    if ((uint) sql_lock->table[i]->reginfo.lock_type > TL_WRITE_ALLOW_WRITE)
     {
       swap_variables(TABLE *, *table, sql_lock->table[i]);
       table++;

sql/mdl.cc

@@ -1689,9 +1689,8 @@ bool MDL_context::acquire_locks(MDL_request_list *mdl_requests,
         shared mode).
 
   @note There can be only one upgrader for a lock or we will have deadlock.
-        This invariant is ensured by code outside of metadata subsystem usually
-        by obtaining some sort of exclusive table-level lock (e.g. TL_WRITE,
-        TL_WRITE_ALLOW_READ) before performing upgrade of metadata lock.
+        This invariant is ensured by the fact that upgradeable locks SNW
+        and SNRW are not compatible with each other and themselves.
 
   @retval FALSE  Success
   @retval TRUE   Failure (thread was killed)

sql/sql_base.cc

@@ -5081,8 +5081,8 @@ static bool check_lock_and_start_stmt(THD *thd,
   else
     lock_type= table_list->lock_type;
 
-  if ((int) lock_type >= (int) TL_WRITE_ALLOW_READ &&
-      (int) table_list->table->reginfo.lock_type < (int) TL_WRITE_ALLOW_READ)
+  if ((int) lock_type > (int) TL_WRITE_ALLOW_WRITE &&
+      (int) table_list->table->reginfo.lock_type <= (int) TL_WRITE_ALLOW_WRITE)
   {
     my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), table_list->alias);
     DBUG_RETURN(1);

sql/sql_table.cc

@@ -4669,7 +4669,7 @@ static bool mysql_admin_table(THD* thd, TABLE_LIST* tables,
       To allow concurrent execution of read-only operations we acquire
       weak metadata lock for them.
     */
-    table->mdl_request.set_type((lock_type >= TL_WRITE_ALLOW_READ) ?
+    table->mdl_request.set_type((lock_type >= TL_WRITE_ALLOW_WRITE) ?
                                 MDL_SHARED_NO_READ_WRITE : MDL_SHARED_READ);
     /* open only one table from local list of command */
     {
@@ -7926,7 +7926,7 @@ bool mysql_recreate_table(THD *thd, TABLE_LIST *table_list)
   /* Same applies to MDL ticket. */
   table_list->mdl_request.ticket= NULL;
   /* Set lock type which is appropriate for ALTER TABLE. */
-  table_list->lock_type= TL_WRITE_ALLOW_READ;
+  table_list->lock_type= TL_READ_NO_INSERT;
   /* Same applies to MDL request. */
   table_list->mdl_request.set_type(MDL_SHARED_NO_WRITE);
 

sql/sql_trigger.cc

@@ -489,7 +489,7 @@ bool mysql_create_or_drop_trigger(THD *thd, TABLE_LIST *tables, bool create)
   else
   {
     tables->table= open_n_lock_single_table(thd, tables,
-                                            TL_WRITE_ALLOW_READ, 0);
+                                            TL_READ_NO_INSERT, 0);
     if (! tables->table)
       goto end;
     tables->table->use_all_columns();

sql/sql_yacc.yy

@@ -697,7 +697,7 @@ static bool add_create_index_prepare (LEX *lex, Table_ident *table)
   lex->sql_command= SQLCOM_CREATE_INDEX;
   if (!lex->current_select->add_table_to_list(lex->thd, table, NULL,
                                               TL_OPTION_UPDATING,
-                                              TL_WRITE_ALLOW_READ,
+                                              TL_READ_NO_INSERT,
                                               MDL_SHARED_NO_WRITE))
     return TRUE;
   lex->alter_info.reset();
@@ -6157,7 +6157,7 @@ alter:
             lex->duplicates= DUP_ERROR; 
             if (!lex->select_lex.add_table_to_list(thd, $4, NULL,
                                                    TL_OPTION_UPDATING,
-                                                   TL_WRITE_ALLOW_READ,
+                                                   TL_READ_NO_INSERT,
                                                    MDL_SHARED_NO_WRITE))
               MYSQL_YYABORT;
             lex->col_list.empty();
@@ -10168,7 +10168,7 @@ drop:
             lex->alter_info.drop_list.push_back(ad);
             if (!lex->current_select->add_table_to_list(lex->thd, $5, NULL,
                                                         TL_OPTION_UPDATING,
-                                                        TL_WRITE_ALLOW_READ,
+                                                        TL_READ_NO_INSERT,
                                                         MDL_SHARED_NO_WRITE))
               MYSQL_YYABORT;
           }
@@ -14094,7 +14094,7 @@ trigger_tail:
             if (!lex->select_lex.add_table_to_list(YYTHD, $9,
                                                    (LEX_STRING*) 0,
                                                    TL_OPTION_UPDATING,
-                                                   TL_WRITE_ALLOW_READ,
+                                                   TL_READ_NO_INSERT,
                                                    MDL_SHARED_NO_WRITE))
               MYSQL_YYABORT;
           }