Public bug reported:
Copy of https://bugs.mysql.com/bug.php?id=79477:
[1 Dec 10:36] Laurynas Biveinis
Description:
InnoDB error monitor thread has code to wake up missed mutex/rwlock waiters.
This code is commented to be necessary in case of lock word reset not being
ordered with waiters flag read properly:
/* A problem: we assume that mutex_reset_lock word
is a memory barrier, that is when we read the waiters
field next, the read must be serialized in memory
after the reset. A speculative processor might
perform the read first, which could leave a waiting
thread hanging indefinitely. */
This code should go away if event-based mutex stays, because:
- all the barriers can be implemented properly using proper means such as
compiler intrincs;
- in case the scenario being protected against happens and this thread saves
the day, it's still possibly a ~0.5 second stall;
- the scenario might happen when the thread is not running (--innodb-read-only,
server startup);
- the scenario might happen on e.g. log sys mutex, and the error monitor thread
itself will block on that mutex at the start of the loop (BTW that code for
checking that LSN is not going backwards could be removed as well);
- less code.
How to repeat:
Code analysis
Suggested fix:
Remove sync_arr_wake_threads_if_sema_free(), sync_arr_cell_can_wake_up(),
sync_array_wake_threads_if_sema_free_low(). Review that the mutex lock_word /
waiters are properly synchronised by barriers.
** Affects: mysql-server
Importance: Unknown
Status: Unknown
** Affects: percona-server
Importance: Wishlist
Status: Triaged
** Affects: percona-server/5.5
Importance: Wishlist
Status: Triaged
** Affects: percona-server/5.6
Importance: Wishlist
Status: Triaged
** Affects: percona-server/5.7
Importance: Wishlist
Assignee: Laurynas Biveinis (laurynas-biveinis)
Status: Fix Committed
** Tags: innodb upstream
** Also affects: percona-server/5.5
Importance: Undecided
Status: New
** Also affects: percona-server/5.7
Importance: Undecided
Status: New
** Also affects: percona-server/5.6
Importance: Undecided
Status: New
** Changed in: percona-server/5.7
Assignee: (unassigned) => Laurynas Biveinis (laurynas-biveinis)
** Changed in: percona-server/5.7
Milestone: None => 5.7.9-1
** Changed in: percona-server/5.7
Importance: Undecided => Wishlist
** Changed in: percona-server/5.6
Importance: Undecided => Wishlist
** Changed in: percona-server/5.5
Importance: Undecided => Wishlist
** Changed in: percona-server/5.5
Status: New => Triaged
** Changed in: percona-server/5.6
Status: New => Triaged
** Changed in: percona-server/5.7
Status: New => In Progress
** Tags added: innodb upstream
** Bug watch added: MySQL Bug System #79477
http://bugs.mysql.com/bug.php?id=79477
** Also affects: mysql-server via
http://bugs.mysql.com/bug.php?id=79477
Importance: Unknown
Status: Unknown
** Changed in: percona-server/5.7
Status: In Progress => Fix Committed
--
You received this bug notification because you are a member of Ubuntu
Server/Client Support Team, which is subscribed to MySQL.
Matching subscriptions: Ubuntu Server/Client Support Team
https://bugs.launchpad.net/bugs/1521564
Title:
Remove sync_arr_wake_threads_if_sema_free hack
To manage notifications about this bug go to:
https://bugs.launchpad.net/mysql-server/+bug/1521564/+subscriptions
--
Mailing list: https://launchpad.net/~enterprise-support
Post to : [email protected]
Unsubscribe : https://launchpad.net/~enterprise-support
More help : https://help.launchpad.net/ListHelp
