fsnotify: add mutex destroy

Call mutex_destroy() before freeing notification group. This only adds
some additional debug checks when mutex debugging is enabled but still
it may be useful.

Link: https://lore.kernel.org/r/20200512181803.405832-1-fabf@skynet.be
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/notify/group.c

@@ -25,6 +25,7 @@ static void fsnotify_final_destroy_group(struct fsnotify_group *group)
 		group->ops->free_group_priv(group);
 
 	mem_cgroup_put(group->memcg);
+	mutex_destroy(&group->mark_mutex);
 
 	kfree(group);
 }