MDEV-23328 Server hang due to Galera lock conflict resolution

Mutex order violation when wsrep bf thread kills a conflicting trx,
the stack is

          wsrep_thd_LOCK()
          wsrep_kill_victim()
          lock_rec_other_has_conflicting()
          lock_clust_rec_read_check_and_lock()
          row_search_mvcc()
          ha_innobase::index_read()
          ha_innobase::rnd_pos()
          handler::ha_rnd_pos()
          handler::rnd_pos_by_record()
          handler::ha_rnd_pos_by_record()
          Rows_log_event::find_row()
          Update_rows_log_event::do_exec_row()
          Rows_log_event::do_apply_event()
          Log_event::apply_event()
          wsrep_apply_events()

and mutexes are taken in the order

          lock_sys->mutex -> victim_trx->mutex -> victim_thread->LOCK_thd_data

When a normal KILL statement is executed, the stack is

          innobase_kill_query()
          kill_handlerton()
          plugin_foreach_with_mask()
          ha_kill_query()
          THD::awake()
          kill_one_thread()

        and mutexes are

          victim_thread->LOCK_thd_data -> lock_sys->mutex -> victim_trx->mutex

This patch is the plan D variant for fixing potetial mutex locking
order exercised by BF aborting and KILL command execution.

In this approach, KILL command is replicated as TOI operation.
This guarantees total isolation for the KILL command execution
in the first node: there is no concurrent replication applying
and no concurrent DDL executing. Therefore there is no risk of
BF aborting to happen in parallel with KILL command execution
either. Potential mutex deadlocks between the different mutex
access paths with KILL command execution and BF aborting cannot
therefore happen.

TOI replication is used, in this approach,  purely as means
to provide isolated KILL command execution in the first node.
KILL command should not (and must not) be applied in secondary
nodes. In this patch, we make this sure by skipping KILL
execution in secondary nodes, in applying phase, where we
bail out if applier thread is trying to execute KILL command.
This is effective, but skipping the applying of KILL command
could happen much earlier as well.

This also fixed unprotected calls to wsrep_thd_abort
that will use wsrep_abort_transaction. This is fixed
by holding THD::LOCK_thd_data while we abort transaction.

Reviewed-by: Jan Lindström <jan.lindstrom@mariadb.com>

1 files changed, 19 insertions, 15 deletions

diff --git a/sql/service_wsrep.cc b/sql/service_wsrep.cc
index 6566bb372d8..18067a4d0ec 100644
--- a/sql/service_wsrep.cc
+++ b/sql/service_wsrep.cc
@@ -1,4 +1,4 @@
-/* Copyright 2018 Codership Oy <info@codership.com>
+/* Copyright 2018-2021 Codership Oy <info@codership.com>
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -29,12 +29,14 @@ extern "C" my_bool wsrep_on(const THD *thd)
 
 extern "C" void wsrep_thd_LOCK(const THD *thd)
 {
+  mysql_mutex_lock(&thd->LOCK_thd_kill);
   mysql_mutex_lock(&thd->LOCK_thd_data);
 }
 
 extern "C" void wsrep_thd_UNLOCK(const THD *thd)
 {
   mysql_mutex_unlock(&thd->LOCK_thd_data);
+  mysql_mutex_unlock(&thd->LOCK_thd_kill);
 }
 
 extern "C" void wsrep_thd_kill_LOCK(const THD *thd)
@@ -189,6 +191,8 @@ extern "C" void wsrep_handle_SR_rollback(THD *bf_thd,
   DBUG_ASSERT(wsrep_thd_is_SR(victim_thd));
   if (!victim_thd || !wsrep_on(bf_thd)) return;
 
+  wsrep_thd_LOCK(victim_thd);
+
   WSREP_DEBUG("handle rollback, for deadlock: thd %llu trx_id %" PRIu64 " frags %zu conf %s",
               victim_thd->thread_id,
               victim_thd->wsrep_trx_id(),
@@ -209,6 +213,9 @@ extern "C" void wsrep_handle_SR_rollback(THD *bf_thd,
   {
     wsrep_thd_self_abort(victim_thd);
   }
+
+  wsrep_thd_UNLOCK(victim_thd);
+
   if (bf_thd)
   {
     wsrep_store_threadvars(bf_thd);
@@ -218,6 +225,9 @@ extern "C" void wsrep_handle_SR_rollback(THD *bf_thd,
 extern "C" my_bool wsrep_thd_bf_abort(THD *bf_thd, THD *victim_thd,
                                       my_bool signal)
 {
+  mysql_mutex_assert_owner(&victim_thd->LOCK_thd_kill);
+  mysql_mutex_assert_owner(&victim_thd->LOCK_thd_data);
+
   DBUG_EXECUTE_IF("sync.before_wsrep_thd_abort",
                  {
                    const char act[]=
@@ -234,28 +244,26 @@ extern "C" my_bool wsrep_thd_bf_abort(THD *bf_thd, THD *victim_thd,
     have wsrep on. Note that this should never interrupt RSU
     as RSU has paused the provider.
    */
+  mysql_mutex_assert_owner(&victim_thd->LOCK_thd_data);
+  mysql_mutex_assert_owner(&victim_thd->LOCK_thd_kill);
+
   if ((ret || !wsrep_on(victim_thd)) && signal)
   {
-    mysql_mutex_assert_not_owner(&victim_thd->LOCK_thd_data);
-    mysql_mutex_assert_not_owner(&victim_thd->LOCK_thd_kill);
-    mysql_mutex_lock(&victim_thd->LOCK_thd_data);
-
     if (victim_thd->wsrep_aborter && victim_thd->wsrep_aborter != bf_thd->thread_id)
     {
       WSREP_DEBUG("victim is killed already by %llu, skipping awake",
                   victim_thd->wsrep_aborter);
-      mysql_mutex_unlock(&victim_thd->LOCK_thd_data);
+      wsrep_thd_UNLOCK(victim_thd);
       return false;
     }
 
-    mysql_mutex_lock(&victim_thd->LOCK_thd_kill);
     victim_thd->wsrep_aborter= bf_thd->thread_id;
     victim_thd->awake_no_mutex(KILL_QUERY);
-    mysql_mutex_unlock(&victim_thd->LOCK_thd_kill);
-    mysql_mutex_unlock(&victim_thd->LOCK_thd_data);
-  } else {
-    WSREP_DEBUG("wsrep_thd_bf_abort skipped awake");
   }
+  else
+    WSREP_DEBUG("wsrep_thd_bf_abort skipped awake for %llu", thd_get_thread_id(victim_thd));
+
+  wsrep_thd_UNLOCK(victim_thd);
   return ret;
 }
 
@@ -280,8 +288,6 @@ extern "C" my_bool wsrep_thd_order_before(const THD *left, const THD *right)
 
 extern "C" my_bool wsrep_thd_is_aborting(const MYSQL_THD thd)
 {
-  mysql_mutex_assert_owner(&thd->LOCK_thd_data);
-
   const wsrep::client_state& cs(thd->wsrep_cs());
   const enum wsrep::transaction::state tx_state(cs.transaction().state());
   switch (tx_state)
@@ -295,8 +301,6 @@ extern "C" my_bool wsrep_thd_is_aborting(const MYSQL_THD thd)
     default:
       return false;
   }
-
-  return false;
 }
 
 static inline enum wsrep::key::type