MDEV-30209 Race condition between fil_node_open_file() and renaming files

mtr_t::commit_file(): Protect the rename operation with fil_system.mutex
like we used to do before commit 2e43af69
in order to prevent fil_node_open_file() from running concurrently.
In other words, fil_system.mutex will protect the consistency of
fil_node_t::name and the file name in the file system.

This race condition should be very hard to trigger. We would need
a low value of innodb_open_files or table_cache limit so that
fil_space_t::try_to_close() will be invoked frequently. Simultaneously
with a RENAME operation, something (such as a write of a data page)
would have to try to open the file.

storage/innobase/mtr/mtr0mtr.cc

@@ -385,15 +385,15 @@ bool mtr_t::commit_file(fil_space_t &space, const char *name)
 
   if (name)
   {
+    char *new_name= mem_strdup(name);
+    mysql_mutex_lock(&fil_system.mutex);
     success= os_file_rename(innodb_data_file_key, old_name, name);
-
     if (success)
-    {
-      mysql_mutex_lock(&fil_system.mutex);
-      space.chain.start->name= mem_strdup(name);
-      mysql_mutex_unlock(&fil_system.mutex);
-      ut_free(old_name);
-    }
+      space.chain.start->name= new_name;
+    else
+      old_name= new_name;
+    mysql_mutex_unlock(&fil_system.mutex);
+    ut_free(old_name);
   }
   else
   {