linux-kernel - Re: [PATCH v4 11/14] Add start_renaming_two

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Message-ID: <20251030062214.GW2441659@ZenIV>
Date: Thu, 30 Oct 2025 06:22:14 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: NeilBrown <neil@...wn.name>
Cc: Christian Brauner <brauner@...nel.org>,
	Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
	Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
	David Howells <dhowells@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
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	Chuck Lever <chuck.lever@...cle.com>,
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	Stefan Berger <stefanb@...ux.ibm.com>,
	"Darrick J. Wong" <djwong@...nel.org>, linux-kernel@...r.kernel.org,
	netfs@...ts.linux.dev, ecryptfs@...r.kernel.org,
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	apparmor@...ts.ubuntu.com, linux-security-module@...r.kernel.org,
	selinux@...r.kernel.org
Subject: Re: [PATCH v4 11/14] Add start_renaming_two_dentries()

On Thu, Oct 30, 2025 at 10:31:11AM +1100, NeilBrown wrote:

> +++ b/fs/debugfs/inode.c

Why does debugfs_change_name() need any of that horror?  Seriously, WTF?
This is strictly a name change on a filesystem that never, ever moves
anything from one directory to another.

IMO struct renamedata is a fucking eyesore, but that aside, this:

> @@ -539,22 +540,30 @@ static int sel_make_policy_nodes(struct selinux_fs_info *fsi,
>  	if (ret)
>  		goto out;
>  
> -	lock_rename(tmp_parent, fsi->sb->s_root);
> +	rd.old_parent = tmp_parent;
> +	rd.new_parent = fsi->sb->s_root;
>  
>  	/* booleans */
> -	d_exchange(tmp_bool_dir, fsi->bool_dir);
> +	ret = start_renaming_two_dentries(&rd, tmp_bool_dir, fsi->bool_dir);
> +	if (!ret) {
> +		d_exchange(tmp_bool_dir, fsi->bool_dir);
>  
> -	swap(fsi->bool_num, bool_num);
> -	swap(fsi->bool_pending_names, bool_names);
> -	swap(fsi->bool_pending_values, bool_values);
> +		swap(fsi->bool_num, bool_num);
> +		swap(fsi->bool_pending_names, bool_names);
> +		swap(fsi->bool_pending_values, bool_values);
>  
> -	fsi->bool_dir = tmp_bool_dir;
> +		fsi->bool_dir = tmp_bool_dir;
> +		end_renaming(&rd);
> +	}
>  
>  	/* classes */
> -	d_exchange(tmp_class_dir, fsi->class_dir);
> -	fsi->class_dir = tmp_class_dir;
> +	ret = start_renaming_two_dentries(&rd, tmp_class_dir, fsi->class_dir);
> +	if (ret == 0) {
> +		d_exchange(tmp_class_dir, fsi->class_dir);
> +		fsi->class_dir = tmp_class_dir;
>  
> -	unlock_rename(tmp_parent, fsi->sb->s_root);
> +		end_renaming(&rd);
> +	}
>  
>  out:
>  	sel_remove_old_bool_data(bool_num, bool_names, bool_values);

is very interesting - suddenly you get two non-overlapping scopes instead of one.
Why is that OK?