mutex_lock(&d_inode(dir)->i_mutex);
list_for_each_entry_safe(dentry, tmp, &dir->d_subdirs, d_child) {
spin_lock(&dentry->d_lock);
mutex_lock(&d_inode(dir)->i_mutex);
list_for_each_entry_safe(dentry, tmp, &dir->d_subdirs, d_child) {
spin_lock(&dentry->d_lock);