MDEV-6616 Server crashes in my_hash_first if shutdown is performed when FLUSH LOGS is running

master_info_index becomes zero during shutdown.
check that it's valid (under a mutex) before dereferencing.

1 files changed, 31 insertions, 26 deletions

diff --git a/sql/sql_reload.cc b/sql/sql_reload.cc
index bb3d5bb899a..95e06ddbbd5 100644
--- a/sql/sql_reload.cc
+++ b/sql/sql_reload.cc
@@ -174,18 +174,21 @@ bool reload_acl_and_cache(THD *thd, unsigned long long options,
     */
     tmp_write_to_binlog= 0;
     mysql_mutex_lock(&LOCK_active_mi);
-    if (!(mi= (master_info_index->
-               get_master_info(&connection_name,
-                               Sql_condition::WARN_LEVEL_ERROR))))
+    if (master_info_index)
     {
-      result= 1;
-    }
-    else
-    {
-      mysql_mutex_lock(&mi->data_lock);
-      if (rotate_relay_log(mi))
-        *write_to_binlog= -1;
-      mysql_mutex_unlock(&mi->data_lock);
+      if (!(mi= (master_info_index->
+                 get_master_info(&connection_name,
+                                 Sql_condition::WARN_LEVEL_ERROR))))
+      {
+        result= 1;
+      }
+      else
+      {
+        mysql_mutex_lock(&mi->data_lock);
+        if (rotate_relay_log(mi))
+          *write_to_binlog= -1;
+        mysql_mutex_unlock(&mi->data_lock);
+      }
     }
     mysql_mutex_unlock(&LOCK_active_mi);
 #endif
@@ -346,22 +349,24 @@ bool reload_acl_and_cache(THD *thd, unsigned long long options,
    Master_info *mi;
    tmp_write_to_binlog= 0;
    mysql_mutex_lock(&LOCK_active_mi);
-
-   if (!(mi= (master_info_index->
-              get_master_info(&lex_mi->connection_name,
-                              Sql_condition::WARN_LEVEL_ERROR))))
+   if (master_info_index)
    {
-     result= 1;
-   }
-   else if (reset_slave(thd, mi))
-   {
-     /* NOTE: my_error() has been already called by reset_slave(). */
-     result= 1;
-   }
-   else if (mi->connection_name.length && thd->lex->reset_slave_info.all)
-   {
-     /* If not default connection and 'all' is used */
-     master_info_index->remove_master_info(&mi->connection_name);
+     if (!(mi= (master_info_index->
+                get_master_info(&lex_mi->connection_name,
+                                Sql_condition::WARN_LEVEL_ERROR))))
+     {
+       result= 1;
+     }
+     else if (reset_slave(thd, mi))
+     {
+       /* NOTE: my_error() has been already called by reset_slave(). */
+       result= 1;
+     }
+     else if (mi->connection_name.length && thd->lex->reset_slave_info.all)
+     {
+       /* If not default connection and 'all' is used */
+       master_info_index->remove_master_info(&mi->connection_name);
+     }
    }
    mysql_mutex_unlock(&LOCK_active_mi);
  }