linux-kernel - Re: [PATCH] fuse: fix conversion of fuse_reverse_inval_entry() to start

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Message-ID: <CAJfpegtJDJL7T0-Uj664xOm4N2e6fyJp_XwFecHX_9e9ipUyEw@mail.gmail.com>
Date: Tue, 2 Dec 2025 09:46:41 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Amir Goldstein <amir73il@...il.com>, NeilBrown <neil@...wn.name>, 
	Christian Brauner <brauner@...nel.org>, Val Packett <val@...kett.cool>, 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>, 
	Danilo Krummrich <dakr@...nel.org>, Tyler Hicks <code@...icks.com>, Chuck Lever <chuck.lever@...cle.com>, 
	Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
	Namjae Jeon <linkinjeon@...nel.org>, Steve French <smfrench@...il.com>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Carlos Maiolino <cem@...nel.org>, 
	John Johansen <john.johansen@...onical.com>, Paul Moore <paul@...l-moore.com>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Stephen Smalley <stephen.smalley.work@...il.com>, Ondrej Mosnacek <omosnace@...hat.com>, 
	Mateusz Guzik <mjguzik@...il.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
	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, linux-nfs@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, linux-cifs@...r.kernel.org, 
	linux-xfs@...r.kernel.org, linux-security-module@...r.kernel.org, 
	selinux@...r.kernel.org
Subject: Re: [PATCH] fuse: fix conversion of fuse_reverse_inval_entry() to start_removing()

On Mon, 1 Dec 2025 at 18:08, Al Viro <viro@...iv.linux.org.uk> wrote:

> Then as far as VFS is concerned, it's an equivalent of "we'd done
> a dcache lookup and revalidate told us to bugger off", which does
> *not* need locking the parent - the same sequence can very well
> happen without touching any inode locks.

Okay.

> IOW, from the point of view of locking protocol changes that's not
> a removal at all.
>
> Or do you need them serialized for fuse-internal purposes?

Not as far as I can see. As to any fuse filesystem being reliant on
this behavior, I think that's unlikely, though it's sort of documented
in the libfuse APIs as:

 * To avoid a deadlock this function must not be called in the
 * execution path of a related filesystem operation or within any code
 * that could hold a lock that could be needed to execute such an
 * operation. As of kernel 4.18, a "related operation" is a lookup(),
 * symlink(), mknod(), mkdir(), unlink(), rename(), link() or create()
 * request for the parent, and a setattr(), unlink(), rmdir(),
 * rename(), setxattr(), removexattr(), readdir() or readdirplus()
 * request for the inode itself.

Why the locking was added in the first place?  Oversight, probably.

Thanks,
Miklos