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Bug #54360 Deadlock DROP/ALTER/CREATE DATABASE with open HANDLER

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This deadlock happened if DROP DATABASE was blocked due to an open
HANDLER table from a different connection. While DROP DATABASE
is blocked, it holds the LOCK_mysql_create_db mutex. This results
in a deadlock if the connection with the open HANDLER table tries
to execute a CREATE/ALTER/DROP DATABASE statement as they all
try to acquire LOCK_mysql_create_db.

This patch makes this deadlock scenario very unlikely by closing and
marking for re-open all HANDLER tables for which there are pending
conflicing locks, before LOCK_mysql_create_db is acquired.
However, there is still a very slight possibility that a connection
could access one of these HANDLER tables between closing/marking for
re-open and the acquisition of LOCK_mysql_create_db.

This patch is for 5.1 only, a separate and complete fix will be
made for 5.5+.

Test case added to schema.test.
This commit is contained in:
Jon Olav Hauglid 2010-06-26 19:36:00 +02:00
parent 8fc01031bf
commit b4593605e0
3 changed files with 102 additions and 0 deletions
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19
mysql-test/r/schema.result
View File

@ -11,3 +11,22 @@ mtr
mysql
test
drop schema foo;
#
# Bug#54360 Deadlock DROP/ALTER/CREATE DATABASE with open HANDLER
#
CREATE DATABASE db1;
CREATE TABLE db1.t1 (a INT);
INSERT INTO db1.t1 VALUES (1), (2);
# Connection con1
HANDLER db1.t1 OPEN;
# Connection default
# Sending:
DROP DATABASE db1;
# Connection con2
# Waiting for 'DROP DATABASE db1' to sync in.
# Connection con1
CREATE DATABASE db2;
ALTER DATABASE db2 DEFAULT CHARACTER SET utf8;
DROP DATABASE db2;
# Connection default
# Reaping: DROP DATABASE db1

47
mysql-test/t/schema.test
View File

@ -4,6 +4,9 @@
# Drop mysqltest1 database, as it can left from the previous tests.
#
# Save the initial number of concurrent sessions.
--source include/count_sessions.inc
--disable_warnings
drop database if exists mysqltest1;
--enable_warnings
@ -12,3 +15,47 @@ create schema foo;
show create schema foo;
show schemas;
drop schema foo;
--echo #
--echo # Bug#54360 Deadlock DROP/ALTER/CREATE DATABASE with open HANDLER
--echo #
CREATE DATABASE db1;
CREATE TABLE db1.t1 (a INT);
INSERT INTO db1.t1 VALUES (1), (2);
--echo # Connection con1
connect (con1, localhost, root);
HANDLER db1.t1 OPEN;
--echo # Connection default
connection default;
--echo # Sending:
--send DROP DATABASE db1
--echo # Connection con2
connect (con2, localhost, root);
--echo # Waiting for 'DROP DATABASE db1' to sync in.
let $wait_condition=SELECT COUNT(*)=1 FROM information_schema.processlist
WHERE state='Waiting for table' AND info='DROP DATABASE db1';
--source include/wait_condition.inc
--echo # Connection con1
connection con1;
# All these statements before resulted in deadlock.
CREATE DATABASE db2;
ALTER DATABASE db2 DEFAULT CHARACTER SET utf8;
DROP DATABASE db2;
--echo # Connection default
connection default;
--echo # Reaping: DROP DATABASE db1
--reap
disconnect con1;
disconnect con2;
# 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

36
sql/sql_db.cc
View File

@ -642,6 +642,18 @@ int mysql_create_db(THD *thd, char *db, HA_CREATE_INFO *create_info,
goto exit2;
}
/*
Close and mark for re-open all HANDLER tables which are marked for flush
or which there are pending conflicing locks against. This is needed to
prevent deadlocks.
*/
if (thd->handler_tables_hash.records)
{
pthread_mutex_lock(&LOCK_open);
mysql_ha_flush(thd);
pthread_mutex_unlock(&LOCK_open);
}
VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
/* Check directory */
@ -788,6 +800,18 @@ bool mysql_alter_db(THD *thd, const char *db, HA_CREATE_INFO *create_info)
if ((error=wait_if_global_read_lock(thd,0,1)))
goto exit2;
/*
Close and mark for re-open all HANDLER tables which are marked for flush
or which there are pending conflicing locks against. This is needed to
prevent deadlocks.
*/
if (thd->handler_tables_hash.records)
{
pthread_mutex_lock(&LOCK_open);
mysql_ha_flush(thd);
pthread_mutex_unlock(&LOCK_open);
}
VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
/*
@ -886,6 +910,18 @@ bool mysql_rm_db(THD *thd,char *db,bool if_exists, bool silent)
goto exit2;
}
/*
Close and mark for re-open all HANDLER tables which are marked for flush
or which there are pending conflicing locks against. This is needed to
prevent deadlocks.
*/
if (thd->handler_tables_hash.records)
{
pthread_mutex_lock(&LOCK_open);
mysql_ha_flush(thd);
pthread_mutex_unlock(&LOCK_open);
}
VOID(pthread_mutex_lock(&LOCK_mysql_create_db));
length= build_table_filename(path, sizeof(path) - 1, db, "", "", 0);