MDEV-21189: Dropping partition with 'wsrep_OSU_method=RSU' and 'SESSION sql_log_bin = 0' cases the galera node to hang

Found two bugs

(1) have_committing_connections was missing mutex unlock on one
exit case. As this function is called on a loop it caused mutex
lock when we already owned the mutex. This could cause hang.

(2) wsrep_RSU_begin did set up error code when partition to
be dropped could not be MDL-locked because of concurrent
operations but wrong error code was propagated to upper layer
causing error to be ignored. This could have also caused
the hang.

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/wsrep_mysqld.cc b/sql/wsrep_mysqld.cc
index 062c9dcd74c..cfcc04bff2c 100644
--- a/sql/wsrep_mysqld.cc
+++ b/sql/wsrep_mysqld.cc
@@ -1784,7 +1784,7 @@ static int wsrep_RSU_begin(THD *thd, char *db_, char *table_)
     }
 
     my_error(ER_LOCK_DEADLOCK, MYF(0));
-    return(1);
+    return(-1);
   }
 
   wsrep_seqno_t seqno = wsrep->pause(wsrep);
@@ -2311,6 +2311,7 @@ static my_bool have_committing_connections()
 
     if (is_committing_connection(tmp))
     {
+      mysql_mutex_unlock(&LOCK_thread_count);
       return TRUE;
     }
   }