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Bug#23713 LOCK TABLES + CREATE TRIGGER + FLUSH TABLES WITH READ LOCK = deadlock

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This bug is actually two bugs in one, one of which is CREATE TRIGGER under
LOCK TABLES and the other is CREATE TRIGGER under LOCK TABLES simultaneous
to a FLUSH TABLES WITH READ LOCK (global read lock). Both situations could
lead to a server crash or deadlock.

The first problem arises from the fact that when under LOCK TABLES, if the
table is in the set of locked tables, the table is already open and it doesn't
need to be reopened (not a placeholder). Also in this case, if the table is
not write locked, a exclusive lock can't be acquired because of a possible
deadlock with another thread also holding a (read) lock on the table. The
second issue arises from the fact that one should never wait for a global
read lock if it's holding any locked tables, because the global read lock
is waiting for these tables and this leads to a circular wait deadlock.

The solution for the first case is to check if the table is write locked
and upgraded the write lock to a exclusive lock and fail otherwise for non
write locked tables. Grabbin the exclusive lock in this case also means
to ensure that the table is opened only by the calling thread. The second
issue is partly fixed by not waiting for the global read lock if the thread
is holding any locked tables.

The second issue is only partly addressed in this patch because it turned
out to be much wider and also affects other DDL statements. Reported as
Bug#32395
This commit is contained in:
davi@mysql.com/endora.local
2007-11-29 09:42:26 -02:00
parent de0175204d
commit d179bb64c2
10 changed files with 207 additions and 47 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
mysql-test/r/trigger.result
View File

@ -1981,4 +1981,39 @@ drop table table_25411_b;
DROP TRIGGER IF EXISTS trg;
SHOW CREATE TRIGGER trg;
ERROR HY000: Trigger does not exist
drop table if exists t1;
create table t1 (i int, j int);
create trigger t1_bi before insert on t1 for each row begin end;
create trigger t1_bi before insert on t1 for each row begin end;
ERROR 42000: This version of MySQL doesn't yet support 'multiple triggers with the same action time and event for one table'
drop trigger t1_bi;
drop trigger t1_bi;
ERROR HY000: Trigger does not exist
lock tables t1 read;
create trigger t1_bi before insert on t1 for each row begin end;
ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
create trigger t1_bi before insert on t1 for each row begin end;
ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
drop trigger t1_bi;
ERROR HY000: Trigger does not exist
unlock tables;
create trigger t1_bi before insert on t1 for each row begin end;
lock tables t1 read;
create trigger t1_bi before insert on t1 for each row begin end;
ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
drop trigger t1_bi;
ERROR HY000: Table 't1' was locked with a READ lock and can't be updated
unlock tables;
drop trigger t1_bi;
lock tables t1 write;
create trigger b1_bi before insert on t1 for each row set new.i = new.i + 10;
insert into t1 values (10, 10);
drop trigger b1_bi;
insert into t1 values (10, 10);
select * from t1;
i j
20 10
10 10
unlock tables;
drop table t1;
End of 5.1 tests.