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MDEV-450: Deadlock between starting a slave and reading system variables

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Starting the SQL thread might deadlock with reading the values of the
replication filtering options.

The deadlock is due to a lock order violation when the variables are
read or set. For example, reading replicate_ignore_table first
acquires LOCK_global_system_variables in sys_var::value_ptr and later
acquires LOCK_active_mi in Sys_var_rpl_filter::global_value_ptr. This
violates the order established when starting a SQL thread, where
LOCK_active_mi is acquired before start_slave, and ends up creating a
thread (handle_slave_sql) that allocates a THD handle whose
constructor acquires LOCK_global_system_variables in THD::init.

The solution is to unlock LOCK_global_system_variables before the
replication filtering options are set or read. This way the lock
order is preserved and the data being read/set is still protected
given that it acquires LOCK_active_mi.
This commit is contained in:
unknown
2012-08-14 12:40:40 +02:00
parent ecc03af931
commit 47929af5e0
5 changed files with 134 additions and 10 deletions
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31
mysql-test/suite/rpl/r/rpl_start_slave_deadlock_sys_vars.result Normal file
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include/master-slave.inc
[connection master]
# connection: slave
SET @save_slave_net_timeout = @@GLOBAL.slave_net_timeout;
STOP SLAVE;
include/wait_for_slave_to_stop.inc
# open an extra connection to the slave
# connection: slave2
# set debug synchronization point
SET DEBUG_SYNC='fix_slave_net_timeout SIGNAL parked WAIT_FOR go';
# attempt to set slave_net_timeout, will wait on sync point
SET @@GLOBAL.slave_net_timeout = 100;
# connection: slave
SET DEBUG_SYNC='now WAIT_FOR parked';
# connection: slave1
# attempt to start the SQL thread
START SLAVE SQL_THREAD;
# connection: slave
# wait until SQL thread has been started
# sleep a bit so that the SQL thread THD handle is initialized
# signal the set slave_net_timeout to continue
SET DEBUG_SYNC='now SIGNAL go';
# connection: slave2
# reap result of set slave_net_timeout
# connection: slave1
# reap result of starting the SQL thread
# disconnect: slave2
# connection: slave
# cleanup
SET @@GLOBAL.slave_net_timeout = @save_slave_net_timeout;
include/rpl_end.inc

57
mysql-test/suite/rpl/t/rpl_start_slave_deadlock_sys_vars.test Normal file
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source include/master-slave.inc;
source include/have_debug_sync.inc;
--echo # connection: slave
connection slave;
SET @save_slave_net_timeout = @@GLOBAL.slave_net_timeout;
STOP SLAVE;
source include/wait_for_slave_to_stop.inc;
--echo # open an extra connection to the slave
connect(slave2,127.0.0.1,root,,test,$SLAVE_MYPORT,);
--echo # connection: slave2
--echo # set debug synchronization point
SET DEBUG_SYNC='fix_slave_net_timeout SIGNAL parked WAIT_FOR go';
--echo # attempt to set slave_net_timeout, will wait on sync point
--send SET @@GLOBAL.slave_net_timeout = 100
--echo # connection: slave
connection slave;
SET DEBUG_SYNC='now WAIT_FOR parked';
--echo # connection: slave1
connection slave1;
--echo # attempt to start the SQL thread
--send START SLAVE SQL_THREAD
--echo # connection: slave
connection slave;
--echo # wait until SQL thread has been started
let $wait_condition=
select count(*) = 1 from information_schema.processlist
where state = "Waiting for slave thread to start" and info = "START SLAVE SQL_THREAD";
--source include/wait_condition.inc
--echo # sleep a bit so that the SQL thread THD handle is initialized
sleep 2;
--echo # signal the set slave_net_timeout to continue
SET DEBUG_SYNC='now SIGNAL go';
--echo # connection: slave2
connection slave2;
--echo # reap result of set slave_net_timeout
--reap
--echo # connection: slave1
connection slave1;
--echo # reap result of starting the SQL thread
--reap
--echo # disconnect: slave2
disconnect slave2;
--echo # connection: slave
connection slave;
--echo # cleanup
SET @@GLOBAL.slave_net_timeout = @save_slave_net_timeout;
source include/rpl_end.inc;