linux-kernel - Re: [PATCH 00/11 RFC] Allow concurrent changes in a directory

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Message-ID: <20241223052243.GL1977892@ZenIV>
Date: Mon, 23 Dec 2024 05:22:43 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: NeilBrown <neilb@...e.de>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/11 RFC] Allow concurrent changes in a directory

On Fri, Dec 20, 2024 at 01:54:18PM +1100, NeilBrown wrote:

> Not all calling code has been converted.  Some callers outside of
> fs/namei.c still take an exclusive lock with i_rw_sem.  Some might never
> be changed.
> 
> As yet this has only been lightly tested as I haven't add foo_shared
> operations to any filesystem yet.

It's still fundamentally broken.  You assume that shared lock on
parent is enough to prevent the parent/name changes of children.
That assumption is simply not true.