MDEV-5345 - Deadlock between mysql_change_user(), SHOW VARIABLES and

            INSTALL PLUGIN

There was mixed lock order between LOCK_plugin, LOCK_global_system_variables
and LOCK_system_variables_hash. This patch ensures that write-lock on
LOCK_system_variables_hash doesn't intersect with LOCK_plugin.

Fixed by moving initialization/deinitialization of plugin options from
plugin_add()/plugin_del() to plugin_initialize()/plugin_deinitalize().
So that plugin options are handled without protection of LOCK_plugin.

1 files changed, 2 insertions, 2 deletions

diff --git a/sql/set_var.cc b/sql/set_var.cc
index 2179f50d266..d4ca335e959 100644
--- a/sql/set_var.cc
+++ b/sql/set_var.cc
@@ -441,10 +441,10 @@ int mysql_del_sys_var_chain(sys_var *first)
 {
   int result= 0;
 
-  /* A write lock should be held on LOCK_system_variables_hash */
-
+  mysql_rwlock_wrlock(&LOCK_system_variables_hash);
   for (sys_var *var= first; var; var= var->next)
     result|= my_hash_delete(&system_variable_hash, (uchar*) var);
+  mysql_rwlock_unlock(&LOCK_system_variables_hash);
 
   return result;
 }