Revert MDEV-18464 and MDEV-12009

This reverts commit 21b2fada7ab7f35c898c02d2f918461409cc9c8e
and commit 81d71ee6b21870772c336bff15b71904914f146a.

The MDEV-18464 change introduces a few data race issues. Contrary to
the documentation, the field trx_t::victim is not always being protected
by lock_sys_t::mutex and trx_t::mutex. Most importantly, it seems
that KILL QUERY could wrongly avoid acquiring both mutexes when
invoking lock_trx_handle_wait_low(), in case another thread had
already set trx->victim=true.

We also revert MDEV-12009, because it should depend on the MDEV-18464
fix being present.

6 files changed, 5 insertions, 27 deletions

diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
index 920f7ac0329..1f060305d4f 100644
--- a/sql/sql_parse.cc
+++ b/sql/sql_parse.cc
@@ -8292,19 +8292,11 @@ kill_one_thread(THD *thd, longlong id, killed_state kill_signal, killed_type typ
       It's ok to also kill DELAYED threads with KILL_CONNECTION instead of
       KILL_SYSTEM_THREAD; The difference is that KILL_CONNECTION may be
       faster and do a harder kill than KILL_SYSTEM_THREAD;
-
-      Note that if thread is wsrep Brute Force or applier thread we
-      allow killing it only when we're SUPER.
     */
 
-    if ((thd->security_ctx->master_access & SUPER_ACL) ||
-	(thd->security_ctx->user_matches(tmp->security_ctx)
-#ifdef WITH_WSREP
-	 &&
-	 !tmp->wsrep_applier &&
-	 !wsrep_thd_is_BF(tmp, false)
-#endif
-	))
+    if (((thd->security_ctx->master_access & SUPER_ACL) ||
+        thd->security_ctx->user_matches(tmp->security_ctx)) &&
+	!wsrep_thd_is_BF(tmp, false))
     {
       tmp->awake(kill_signal);
       error=0;
diff --git a/sql/sql_plugin_services.ic b/sql/sql_plugin_services.ic
index d70c76701fd..427d8937c57 100644
--- a/sql/sql_plugin_services.ic
+++ b/sql/sql_plugin_services.ic
@@ -181,8 +181,7 @@ static struct wsrep_service_st wsrep_handler = {
   wsrep_trx_is_aborting,
   wsrep_trx_order_before,
   wsrep_unlock_rollback,
-  wsrep_set_data_home_dir,
-  wsrep_thd_is_applier,
+  wsrep_set_data_home_dir
 };
 
 static struct thd_specifics_service_st thd_specifics_handler=
diff --git a/sql/wsrep_dummy.cc b/sql/wsrep_dummy.cc
index e2a4dcf3bad..795e2d19252 100644
--- a/sql/wsrep_dummy.cc
+++ b/sql/wsrep_dummy.cc
@@ -20,9 +20,6 @@
 my_bool wsrep_thd_is_BF(THD *, my_bool)
 { return 0; }
 
-my_bool wsrep_thd_is_applier(THD *)
-{ return 0; }
-
 int wsrep_trx_order_before(THD *, THD *)
 { return 0; }
 
diff --git a/sql/wsrep_mysqld.cc b/sql/wsrep_mysqld.cc
index 82415691b3f..ee8509e3fa2 100644
--- a/sql/wsrep_mysqld.cc
+++ b/sql/wsrep_mysqld.cc
@@ -2470,6 +2470,7 @@ extern "C" void wsrep_thd_set_exec_mode(THD *thd, enum wsrep_exec_mode mode)
   thd->wsrep_exec_mode= mode;
 }
 
+
 extern "C" void wsrep_thd_set_query_state(
 	THD *thd, enum wsrep_query_state state)
 {
diff --git a/sql/wsrep_thd.cc b/sql/wsrep_thd.cc
index 91f0e1e8d8a..551e710cfeb 100644
--- a/sql/wsrep_thd.cc
+++ b/sql/wsrep_thd.cc
@@ -596,15 +596,6 @@ my_bool wsrep_thd_is_BF(THD *thd, my_bool sync)
   return status;
 }
 
-my_bool wsrep_thd_is_applier(THD *thd)
-{
-  my_bool ret = FALSE;
-  if (thd) {
-      ret = thd->wsrep_applier;
-  }
-  return ret;
-}
-
 extern "C"
 my_bool wsrep_thd_is_BF_or_commit(void *thd_ptr, my_bool sync)
 {
diff --git a/sql/wsrep_thd.h b/sql/wsrep_thd.h
index f5fcb50280c..5900668f3fb 100644
--- a/sql/wsrep_thd.h
+++ b/sql/wsrep_thd.h
@@ -37,7 +37,6 @@ int  wsrep_abort_thd(void *bf_thd_ptr, void *victim_thd_ptr,
 */
 extern void  wsrep_thd_set_PA_safe(void *thd_ptr, my_bool safe);
 extern my_bool  wsrep_thd_is_BF(THD *thd, my_bool sync);
-extern my_bool wsrep_thd_is_applier(THD *thd);
 extern my_bool wsrep_thd_is_wsrep(void *thd_ptr);
 
 enum wsrep_conflict_state wsrep_thd_conflict_state(void *thd_ptr, my_bool sync);
@@ -48,7 +47,6 @@ extern "C" int  wsrep_thd_in_locking_session(void *thd_ptr);
 #else /* WITH_WSREP */
 
 #define wsrep_thd_is_BF(T, S) (0)
-#define wsrep_thd_is_applier(T) (0)
 #define wsrep_abort_thd(X,Y,Z) do { } while(0)
 #define wsrep_create_appliers(T) do { } while(0)