MDEV-25037 : SIGSEGV in MDL_lock::hog_lock_types_bitmap

We should not call mdl_context.release_explicit_locks() in
Wsrep_client_service::bf_rollback() if client is quiting because
it will be done again in THD::cleanup().

Note that problem with GET_LOCK() / RELEASE_LOCK() will be fixed
on MDEV-30473.

mysql-test/suite/galera/r/galera_backup_start.result

+connection node_2;
+connection node_1;
+BACKUP STAGE START;
+START TRANSACTION;
+COMMIT;
+BACKUP STAGE END;

mysql-test/suite/galera/t/galera_backup_start.test

+--source include/galera_cluster.inc
+
+BACKUP STAGE START;
+START TRANSACTION;
+COMMIT;
+BACKUP STAGE END;

sql/wsrep_client_service.cc

-/* Copyright 2018-2022 Codership Oy <info@codership.com>
+/* Copyright 2018-2023 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
@@ -349,22 +349,36 @@ void Wsrep_client_service::debug_crash(const char* crash_point)
 int Wsrep_client_service::bf_rollback()
 {
   DBUG_ASSERT(m_thd == current_thd);
-  DBUG_ENTER("Wsrep_client_service::rollback");
+  DBUG_ENTER("Wsrep_client_service::bf_rollback");
 
   int ret= (trans_rollback_stmt(m_thd) || trans_rollback(m_thd));
-  if (m_thd->locked_tables_mode && m_thd->lock)
-  {
-    if (m_thd->locked_tables_list.unlock_locked_tables(m_thd))
-      ret= 1;
-    m_thd->variables.option_bits&= ~OPTION_TABLE_LOCK;
-  }
-  if (m_thd->global_read_lock.is_acquired())
+
+  WSREP_DEBUG("::bf_rollback() thread: %lu, client_state %s "
+              "client_mode %s trans_state %s killed %d",
+              thd_get_thread_id(m_thd),
+              wsrep_thd_client_state_str(m_thd),
+              wsrep_thd_client_mode_str(m_thd),
+              wsrep_thd_transaction_state_str(m_thd),
+              m_thd->killed);
+
+  /* If client is quiting all below will be done in THD::cleanup()
+     TODO: why we need this any other case?  */
+  if (m_thd->wsrep_cs().state() != wsrep::client_state::s_quitting)
   {
-    m_thd->global_read_lock.unlock_global_read_lock(m_thd);
+    if (m_thd->locked_tables_mode && m_thd->lock)
+    {
+      if (m_thd->locked_tables_list.unlock_locked_tables(m_thd))
+        ret= 1;
+      m_thd->variables.option_bits&= ~OPTION_TABLE_LOCK;
+    }
+    if (m_thd->global_read_lock.is_acquired())
+    {
+      m_thd->global_read_lock.unlock_global_read_lock(m_thd);
+    }
+    m_thd->release_transactional_locks();
+    mysql_ull_cleanup(m_thd);
+    m_thd->mdl_context.release_explicit_locks();
   }
-  m_thd->release_transactional_locks();
-  mysql_ull_cleanup(m_thd);
-  m_thd->mdl_context.release_explicit_locks();
 
   DBUG_RETURN(ret);
 }

sql/wsrep_high_priority_service.cc

@@ -292,6 +292,7 @@ int Wsrep_high_priority_service::append_fragment_and_commit(
 
   ret= ret || trans_commit(m_thd);
   ret= ret || (m_thd->wsrep_cs().after_applying(), 0);
+
   m_thd->release_transactional_locks();
 
   free_root(m_thd->mem_root, MYF(MY_KEEP_PREALLOC));
@@ -380,6 +381,15 @@ int Wsrep_high_priority_service::rollback(const wsrep::ws_handle& ws_handle,
      assert(ws_handle == wsrep::ws_handle());
   }
   int ret= (trans_rollback_stmt(m_thd) || trans_rollback(m_thd));
+
+  WSREP_DEBUG("::rollback() thread: %lu, client_state %s "
+              "client_mode %s trans_state %s killed %d",
+              thd_get_thread_id(m_thd),
+              wsrep_thd_client_state_str(m_thd),
+              wsrep_thd_client_mode_str(m_thd),
+              wsrep_thd_transaction_state_str(m_thd),
+              m_thd->killed);
+
   m_thd->release_transactional_locks();
   mysql_ull_cleanup(m_thd);
   m_thd->mdl_context.release_explicit_locks();