database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-30 16:24:05 +03:00
Code Activity

MDEV-21910 Deadlock between BF abort and manual KILL command

Browse Source 
When high priority replication slave applier encounters lock conflict in innodb,
it will force the conflicting lock holder transaction (victim) to rollback.
This is a must in multi-master sychronous replication model to avoid cluster lock-up.
This high priority victim abort (aka "brute force" (BF) abort), is started
from innodb lock manager while holding the victim's transaction's (trx) mutex.
Depending on the execution state of the victim transaction, it may happen that the
BF abort will call for THD::awake() to wake up the victim transaction for the rollback.
Now, if BF abort requires THD::awake() to be called, then the applier thread executed
locking protocol of: victim trx mutex -> victim THD::LOCK_thd_data

If, at the same time another DBMS super user issues KILL command to abort the same victim,
it will execute locking protocol of: victim THD::LOCK_thd_data  -> victim trx mutex.
These two locking protocol acquire mutexes in opposite order, hence unresolvable mutex locking
deadlock may occur.

The fix in this commit adds THD::wsrep_aborter flag to synchronize who can kill the victim
This flag is set both when BF is called for from innodb and by KILL command.
Either path of victim killing will bail out if victim's wsrep_killed is already
set to avoid mutex conflicts with the other aborter execution. THD::wsrep_aborter
records the aborter THD's ID. This is needed to preserve the right to kill
the victim from different locations for the same aborter thread.
It is also good error logging, to see who is reponsible for the abort.

A new test case was added in galera.galera_bf_kill_debug.test for scenario where
wsrep applier thread and manual KILL command try to kill same idle victim
This commit is contained in:
sjaakola
2020-05-19 11:12:26 +03:00
committed by Jan Lindström
parent 141b390d82
commit 5a7794d3a8
15 changed files with 290 additions and 73 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
sql/sql_parse.cc
View File

@ -9048,7 +9048,6 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
uint error= (type == KILL_TYPE_QUERY ? ER_NO_SUCH_QUERY : ER_NO_SUCH_THREAD);
DBUG_ENTER("kill_one_thread");
DBUG_PRINT("enter", ("id: %lld signal: %u", id, (uint) kill_signal));
WSREP_DEBUG("kill_one_thread %llu", thd->thread_id);
if (id && (tmp= find_thread_by_id(id, type == KILL_TYPE_QUERY)))
{
/*
@ -9081,12 +9080,29 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
thd->security_ctx->user_matches(tmp->security_ctx))
#endif /* WITH_WSREP */
{
tmp->awake_no_mutex(kill_signal);
error=0;
#ifdef WITH_WSREP
DEBUG_SYNC(thd, "before_awake_no_mutex");
if (tmp->wsrep_aborter && tmp->wsrep_aborter != thd->thread_id)
{
/* victim is in hit list already, bail out */
WSREP_DEBUG("victim has wsrep aborter: %lu, skipping awake()",
tmp->wsrep_aborter);
error= 0;
}
else
#endif /* WITH_WSREP */
{
WSREP_DEBUG("kill_one_thread %llu, victim: %llu wsrep_aborter %llu by signal %d",
thd->thread_id, id, tmp->wsrep_aborter, kill_signal);
tmp->awake_no_mutex(kill_signal);
WSREP_DEBUG("victim: %llu taken care of", id);
error= 0;
}
}
else
error= (type == KILL_TYPE_QUERY ? ER_KILL_QUERY_DENIED_ERROR :
ER_KILL_DENIED_ERROR);
if (WSREP(tmp)) mysql_mutex_unlock(&tmp->LOCK_thd_data);
mysql_mutex_unlock(&tmp->LOCK_thd_kill);
}