Backport of:

------------------------------------------------------------
revno: 2476.784.3
committer: davi@moksha.local
timestamp: Tue 2007-10-02 21:27:31 -0300
message:
Bug#25858 Some DROP TABLE under LOCK TABLES can cause deadlocks
        
When a client (connection) holds a lock on a table and attempts to
drop (obtain a exclusive lock) on a second table that is already
held by a second client and the second client then attempts to
drop the table that is held by the first client, leads to a
circular wait deadlock. This scenario is very similar to trying to
drop (or rename) a table while holding read locks and are
correctly forbidden.
        
The solution is to allow a drop table operation to continue only
if the table being dropped is write (exclusively) locked, or if
the table is temporary, or if the client is not holding any
locks. Using this scheme prevents the creation of a circular
chain in which each client is waiting for one table that the
next client in the chain is holding.
            
This is incompatible change, as can be seen by number of tests
cases that needed to be fixed, but is consistent with respect to
behavior of the different scenarios in which the circular wait
might happen.

mysql-test/r/drop.result

@@ -86,6 +86,26 @@ select 1;
 1
 1
 unlock tables;
+drop table if exists t1,t2;
+create table t1 (a int);
+create table t2 (a int);
+lock table t1 read;
+drop table t2;
+ERROR HY000: Table 't2' was not locked with LOCK TABLES
+drop table t1;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+unlock tables;
+drop table t1,t2;
+create table t1 (i int);
+create table t2 (i int);
+lock tables t1 read;
+lock tables t2 read;
+drop table t1;
+ERROR HY000: Table 't1' was not locked with LOCK TABLES
+drop table t1,t2;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+unlock tables;
+drop table t1,t2;
 End of 5.0 tests
 create database mysql_test;
 create table mysql_test.t1(f1 int);

mysql-test/r/group_by.result

@@ -107,8 +107,9 @@ SELECT cid, CONCAT(firstname, ' ', surname), COUNT(call_id) FROM t1 LEFT JOIN t2
 cid	CONCAT(firstname, ' ', surname)	COUNT(call_id)
 SELECT HIGH_PRIORITY cid, CONCAT(firstname, ' ', surname), COUNT(call_id) FROM t1 LEFT JOIN t2 ON cid=contact_id WHERE firstname like '%foo%' GROUP BY cid ORDER BY surname, firstname;
 cid	CONCAT(firstname, ' ', surname)	COUNT(call_id)
-drop table t1,t2;
+drop table t2;
 unlock tables;
+drop table t1;
 CREATE TABLE t1 (
 bug_id mediumint(9) NOT NULL auto_increment,
 groupset bigint(20) DEFAULT '0' NOT NULL,

mysql-test/r/insert_notembedded.result

@@ -122,5 +122,6 @@ a	b
 connection: default
 select * from t1;
 a	b
+unlock tables;
 drop table t1;
 set low_priority_updates=default;

mysql-test/r/lock.result

@@ -48,6 +48,9 @@ unlock tables;
 lock tables t1 write, t1 as t1_alias read;
 insert into t1 select index1,nr from t1 as t1_alias;
 drop table t1,t2;
+ERROR HY000: Table 't2' was not locked with LOCK TABLES
+unlock tables;
+drop table t1,t2;
 create table t1 (c1 int);
 create table t2 (c1 int);
 create table t3 (c1 int);
@@ -69,6 +72,9 @@ ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
 delete t2 from t1,t2 where t1.a=t2.a;
 ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
 drop table t1,t2;
+ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
+unlock tables;
+drop table t2,t1;
 End of 4.1 tests.
 drop table if exists t1;
 create table t1 (a int);

mysql-test/r/lock_multi.result

@@ -27,6 +27,7 @@ update t1,t2 set c=a where b=d;
 select c from t2;
 c
 2
+unlock tables;
 drop table t1;
 drop table t2;
 create table t1 (a int);

mysql-test/r/myisam.result

@@ -529,6 +529,7 @@ select straight_join * from t1,t2 force index (primary) where t1.a=t2.a;
 a	a	b
 1	1	1
 2	2	1
+unlock tables;
 drop table t1,t2;
 CREATE TABLE t1 (c1 varchar(250) NOT NULL);
 CREATE TABLE t2 (c1 varchar(250) NOT NULL, PRIMARY KEY (c1));
@@ -542,6 +543,7 @@ INSERT INTO t2 VALUES ('test000001'), ('test000005');
 SELECT t1.c1 AS t1c1, t2.c1 AS t2c1 FROM t1, t2
 WHERE t1.c1 = t2.c1 HAVING t1c1 != t2c1;
 t1c1	t2c1
+UNLOCK TABLES;
 DROP TABLE t1,t2;
 CREATE TABLE t1 (`a` int(11) NOT NULL default '0', `b` int(11) NOT NULL default '0', UNIQUE KEY `a` USING RTREE (`a`,`b`)) ENGINE=MyISAM;
 Got one of the listed errors

mysql-test/r/query_cache_notembedded.result

@@ -93,6 +93,7 @@ a
 3
 SELECT * FROM t1;
 a
+UNLOCK TABLES;
 drop table t1;
 flush query cache;
 reset query cache;

mysql-test/r/view.result

@@ -1104,6 +1104,9 @@ select * from t2;
 ERROR HY000: Table 't2' was not locked with LOCK TABLES
 drop view v1;
 drop table t1, t2;
+ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
+unlock tables;
+drop table t1, t2;
 create table t1 (a int);
 create view v1 as select * from t1 where a < 2 with check option;
 insert into v1 values(1);

mysql-test/t/drop.test

@@ -124,6 +124,39 @@ disconnect addconroot1;
 --source include/wait_until_disconnected.inc
 connection default;
 
+#
+# Bug#25858 Some DROP TABLE under LOCK TABLES can cause deadlocks
+#
+
+--disable_warnings
+drop table if exists t1,t2;
+--enable_warnings
+create table t1 (a int);
+create table t2 (a int);
+lock table t1 read;
+--error ER_TABLE_NOT_LOCKED
+drop table t2;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+drop table t1;
+unlock tables;
+drop table t1,t2;
+connect (addconroot, localhost, root,,);
+connection default;
+create table t1 (i int);
+create table t2 (i int);
+lock tables t1 read;
+connection addconroot;
+lock tables t2 read;
+--error ER_TABLE_NOT_LOCKED
+drop table t1;
+connection default;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+drop table t1,t2;
+disconnect addconroot;
+connection default;
+unlock tables;
+drop table t1,t2;
+
 --echo End of 5.0 tests
 
 #

mysql-test/t/group_by.test

@@ -120,8 +120,9 @@ SELECT cid, CONCAT(firstname, ' ', surname), COUNT(call_id) FROM t1 LEFT JOIN t2
 SELECT cid, CONCAT(firstname, ' ', surname), COUNT(call_id) FROM t1 LEFT JOIN t2 ON cid=contact_id WHERE firstname like '%foo%' GROUP BY cid ORDER BY NULL;
 SELECT HIGH_PRIORITY cid, CONCAT(firstname, ' ', surname), COUNT(call_id) FROM t1 LEFT JOIN t2 ON cid=contact_id WHERE firstname like '%foo%' GROUP BY cid ORDER BY surname, firstname;
 
-drop table t1,t2;
+drop table t2;
 unlock tables;
+drop table t1;
 
 #
 # Test of group by bug in bugzilla

mysql-test/t/insert_notembedded.test

@@ -185,5 +185,6 @@ select * from t1;
 connection default;
 disconnect update;
 disconnect select;
+unlock tables;
 drop table t1;
 set low_priority_updates=default;

mysql-test/t/lock.test

@@ -58,6 +58,9 @@ insert into t1 select index1,nr from t1;
 unlock tables;
 lock tables t1 write, t1 as t1_alias read;
 insert into t1 select index1,nr from t1 as t1_alias;
+--error ER_TABLE_NOT_LOCKED
+drop table t1,t2;
+unlock tables;
 drop table t1,t2;
 
 #
@@ -90,7 +93,10 @@ delete t1 from t1,t2 where t1.a=t2.a;
 delete from t2 using t1,t2 where t1.a=t2.a;
 --error 1099
 delete t2 from t1,t2 where t1.a=t2.a;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
 drop table t1,t2;
+unlock tables;
+drop table t2,t1;
 
 --echo End of 4.1 tests.
 

mysql-test/t/lock_multi.test

@@ -76,6 +76,7 @@ update t1,t2 set c=a where b=d;
 connection reader;
 select c from t2;
 connection locker;
+unlock tables;
 drop table t1;
 drop table t2;
 

mysql-test/t/myisam.test

@@ -503,6 +503,7 @@ insert into t2 values(2,0);
 disconnect root;
 connection default;
 select straight_join * from t1,t2 force index (primary) where t1.a=t2.a;
+unlock tables;
 drop table t1,t2;
 #
 # Full key.
@@ -520,6 +521,7 @@ disconnect con1;
 connection default;
 SELECT t1.c1 AS t1c1, t2.c1 AS t2c1 FROM t1, t2
   WHERE t1.c1 = t2.c1 HAVING t1c1 != t2c1;
+UNLOCK TABLES;
 DROP TABLE t1,t2;
 
 # End of 4.0 tests

mysql-test/t/query_cache_notembedded.test

@@ -99,6 +99,7 @@ connection root2;
 SELECT * FROM t1;
 connection root;
 SELECT * FROM t1;
+UNLOCK TABLES;
 drop table t1;
 connection default;
 disconnect root;

mysql-test/t/view.test

@@ -1017,6 +1017,9 @@ select * from v1;
 -- error ER_TABLE_NOT_LOCKED
 select * from t2;
 drop view v1;
+--error ER_TABLE_NOT_LOCKED_FOR_WRITE
+drop table t1, t2;
+unlock tables;
 drop table t1, t2;
 
 #

sql/lock.cc

@@ -1028,6 +1028,7 @@ int lock_table_name(THD *thd, TABLE_LIST *table_list, bool check_in_use)
   char  key[MAX_DBKEY_LENGTH];
   char *db= table_list->db;
   uint  key_length;
+  bool  found_locked_table= FALSE;
   HASH_SEARCH_STATE state;
   DBUG_ENTER("lock_table_name");
   DBUG_PRINT("enter",("db: %s  name: %s", db, table_list->table_name));
@@ -1043,6 +1044,13 @@ int lock_table_name(THD *thd, TABLE_LIST *table_list, bool check_in_use)
          table = (TABLE*) my_hash_next(&open_cache,(uchar*) key,
                                        key_length, &state))
     {
+      if (table->reginfo.lock_type < TL_WRITE)
+      {
+        if (table->in_use == thd)
+          found_locked_table= TRUE;
+        continue;
+      }
+
       if (table->in_use == thd)
       {
         DBUG_PRINT("info", ("Table is in use"));
@@ -1053,6 +1061,17 @@ int lock_table_name(THD *thd, TABLE_LIST *table_list, bool check_in_use)
     }
   }
 
+  if (thd->locked_tables && thd->locked_tables->table_count &&
+      ! find_temporary_table(thd, table_list->db, table_list->table_name))
+  {
+    if (found_locked_table)
+      my_error(ER_TABLE_NOT_LOCKED_FOR_WRITE, MYF(0), table_list->alias);
+    else
+      my_error(ER_TABLE_NOT_LOCKED, MYF(0), table_list->alias);
+
+    DBUG_RETURN(-1);
+  }
+
   if (!(table= table_cache_insert_placeholder(thd, key, key_length)))
     DBUG_RETURN(-1);