database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-29 05:21:33 +03:00
Code Activity

MDEV-10653: SHOW SLAVE STATUS Can Deadlock an Errored Slave

Browse Source 
AKA rpl.rpl_parallel, binlog_encryption.rpl_parallel fails in
buildbot with timeout in include

A replication parallel worker thread can deadlock with another
connection running SHOW SLAVE STATUS. That is, if the replication
worker thread is in do_gco_wait() and is killed, it will already
hold the LOCK_parallel_entry, and during error reporting, try to
grab the err_lock. SHOW SLAVE STATUS, however, grabs these locks in
reverse order. It will initially grab the err_lock, and then try to
grab LOCK_parallel_entry. This leads to a deadlock when both threads
have grabbed their first lock without the second.

This patch implements the MDEV-31894 proposed fix to optimize the
workers_idle() check to compare the last in-use relay log’s
queued_count==dequeued_count for idleness. This removes the need for
workers_idle() to grab LOCK_parallel_entry, as these values are
atomically updated.

Huge thanks to Kristian Nielsen for diagnosing the problem!

Reviewed By:
============
Kristian Nielsen <knielsen@knielsen-hq.org>
Andrei Elkin <andrei.elkin@mariadb.com>
This commit is contained in:
Brandon Nesterenko
2023-11-29 06:53:31 -07:00
parent 5ca63b2b8b
commit 8dad51481b
6 changed files with 203 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
sql/slave.cc
View File

@ -3123,6 +3123,14 @@ static bool send_show_master_info_data(THD *thd, Master_info *mi, bool full,
mysql_mutex_lock(&mi->err_lock);
/* err_lock is to protect mi->rli.last_error() */
mysql_mutex_lock(&mi->rli.err_lock);
DBUG_EXECUTE_IF("hold_sss_with_err_lock", {
DBUG_ASSERT(!debug_sync_set_action(
thd, STRING_WITH_LEN("now SIGNAL sss_got_err_lock "
"WAIT_FOR sss_continue")));
DBUG_SET("-d,hold_sss_with_err_lock");
});
protocol->store(mi->host, &my_charset_bin);
protocol->store(mi->user, &my_charset_bin);
protocol->store((uint32) mi->port);
@ -3197,7 +3205,8 @@ static bool send_show_master_info_data(THD *thd, Master_info *mi, bool full,
while the slave is processing ignored events, such as those skipped
due to slave_skip_counter.
*/
if (mi->using_parallel() && idle && !mi->rli.parallel.workers_idle())
if (mi->using_parallel() && idle &&
!rpl_parallel::workers_idle(&mi->rli))
idle= false;
}
if (idle)