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MDEV-32728: Wrong mutex usage 'LOCK_thd_data' and 'wait_mutex'

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Checking for kill with thd_kill_level() or check_killed() runs apc
requests, which takes the LOCK_thd_kill mutex. But this is dangerous,
as checking for kill needs to be called while holding many different
mutexes, and can lead to cyclic mutex dependency and deadlock.

But running apc is only "best effort", so skip running the apc if the
LOCK_thd_kill is not available. The apc will then be run on next check
of kill signal.

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
This commit is contained in:
Kristian Nielsen 2023-11-08 13:55:03 +01:00 committed by Sergei Golubchik
parent fefd6d5559
commit 2a4c573339
5 changed files with 11 additions and 8 deletions
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9
sql/my_apc.cc
View File

@ -197,13 +197,16 @@ bool Apc_target::make_apc_call(THD *caller_thd, Apc_call *call,
This should be called periodically by the APC target thread.
*/
void Apc_target::process_apc_requests()
void Apc_target::process_apc_requests(bool force)
{
while (1)
{
Call_request *request;
mysql_mutex_lock(LOCK_thd_kill_ptr);
if (force)
mysql_mutex_lock(LOCK_thd_kill_ptr);
else if (mysql_mutex_trylock(LOCK_thd_kill_ptr))
break; // Mutex is blocked, try again later
if (!(request= get_first_in_queue()))
{
/* No requests in the queue */

4
sql/my_apc.h
View File

@ -70,10 +70,10 @@ public:
bool process= !--enabled && have_apc_requests();
mysql_mutex_unlock(LOCK_thd_kill_ptr);
if (unlikely(process))
process_apc_requests();
process_apc_requests(true);
}
void process_apc_requests();
void process_apc_requests(bool force);
/*
A lightweight function, intended to be used in frequent checks like this:

2
sql/sql_class.cc
View File

@ -4724,7 +4724,7 @@ extern "C" enum thd_kill_levels thd_kill_level(const MYSQL_THD thd)
if (unlikely(apc_target->have_apc_requests()))
{
if (thd == current_thd)
apc_target->process_apc_requests();
apc_target->process_apc_requests(false);
}
return THD_IS_NOT_KILLED;
}

2
sql/sql_class.h
View File

@ -3606,7 +3606,7 @@ public:
return TRUE;
}
if (apc_target.have_apc_requests())
apc_target.process_apc_requests();
apc_target.process_apc_requests(false);
return FALSE;
}

2
unittest/sql/my_apc-t.cc
View File

@ -100,7 +100,7 @@ void *test_apc_service_thread(void *ptr)
//apc_target.enable();
for (int i = 0; i < 10 && !service_should_exit; i++)
{
apc_target.process_apc_requests();
apc_target.process_apc_requests(true);
my_sleep(int_rand(30));
}
}