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Bug #34305 show slave status handling segfaults when slave io is about

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The artifact was caused by
a flaw in concurrent accessing the slave's io thd by
the io itself and a handling show slave status thread.
Namely, show_master_info did not acquire mi->run_lock mutex that is
specified for mi->io_thd member.

Fixed with deploying the mutex locking and unlocking. The mutex is kept
short time and without interleaving with mi->data_lock mutex.

Todo: to report and fix an issue with 
    sys_var_slave_skip_counter::{methods} 
seem to acquire incorrectly
     active_mi->rli.run_lock
instead of the specified
     active_mi->rli.data_lock

A test case is difficult to compose, so rpl_packet should continue serving
as the indicator.
This commit is contained in:
aelkin/elkin@koti.dsl.inet.fi
2008-02-05 17:36:26 +02:00
parent 69fdf6794a
commit 51b33ea35d
2 changed files with 8 additions and 7 deletions
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11
sql/slave.cc
View File

@ -2447,14 +2447,15 @@ bool show_master_info(THD* thd, MASTER_INFO* mi)
protocol->prepare_for_resend();
/*
TODO: we read slave_running without run_lock, whereas these variables
are updated under run_lock and not data_lock. In 5.0 we should lock
run_lock on top of data_lock (with good order).
slave_running can be accessed without run_lock but not other
non-volotile members like mi->io_thd, which is guarded by the mutex.
*/
pthread_mutex_lock(&mi->run_lock);
protocol->store(mi->io_thd ? mi->io_thd->proc_info : "", &my_charset_bin);
pthread_mutex_unlock(&mi->run_lock);
pthread_mutex_lock(&mi->data_lock);
pthread_mutex_lock(&mi->rli.data_lock);
protocol->store(mi->io_thd ? mi->io_thd->proc_info : "", &my_charset_bin);
protocol->store(mi->host, &my_charset_bin);
protocol->store(mi->user, &my_charset_bin);
protocol->store((uint32) mi->port);

4
sql/slave.h
View File

@ -65,8 +65,8 @@
mi->rli does not either.
In MASTER_INFO: run_lock, data_lock
run_lock protects all information about the run state: slave_running, and the
existence of the I/O thread (to stop/start it, you need this mutex).
run_lock protects all information about the run state: slave_running, thd
and the existence of the I/O thread to stop/start it, you need this mutex).
data_lock protects some moving members of the struct: counters (log name,
position) and relay log (MYSQL_LOG object).