linux-kernel - Re: [PATCH 04/11] VFS: introduce dentry_lookup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-id: <175507162200.2234665.9318589188954309739@noble.neil.brown.name>
Date: Wed, 13 Aug 2025 17:53:42 +1000
From: "NeilBrown" <neil@...wn.name>
To: "Al Viro" <viro@...iv.linux.org.uk>
Cc: "Christian Brauner" <brauner@...nel.org>, "Jan Kara" <jack@...e.cz>,
 "David Howells" <dhowells@...hat.com>,
 "Marc Dionne" <marc.dionne@...istor.com>, "Xiubo Li" <xiubli@...hat.com>,
 "Ilya Dryomov" <idryomov@...il.com>, "Tyler Hicks" <code@...icks.com>,
 "Miklos Szeredi" <miklos@...redi.hu>, "Richard Weinberger" <richard@....at>,
 "Anton Ivanov" <anton.ivanov@...bridgegreys.com>,
 "Johannes Berg" <johannes@...solutions.net>,
 "Trond Myklebust" <trondmy@...nel.org>, "Anna Schumaker" <anna@...nel.org>,
 "Chuck Lever" <chuck.lever@...cle.com>, "Jeff Layton" <jlayton@...nel.org>,
 "Amir Goldstein" <amir73il@...il.com>, "Steve French" <sfrench@...ba.org>,
 "Namjae Jeon" <linkinjeon@...nel.org>, "Carlos Maiolino" <cem@...nel.org>,
 linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org,
 netfs@...ts.linux.dev, ceph-devel@...r.kernel.org, ecryptfs@...r.kernel.org,
 linux-um@...ts.infradead.org, linux-nfs@...r.kernel.org,
 linux-unionfs@...r.kernel.org, linux-cifs@...r.kernel.org,
 linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] VFS: introduce dentry_lookup_continue()

On Wed, 13 Aug 2025, Al Viro wrote:
> On Tue, Aug 12, 2025 at 12:25:07PM +1000, NeilBrown wrote:
> > A few callers operate on a dentry which they already have - unlike the
> > normal case where a lookup proceeds an operation.
> > 
> > For these callers dentry_lookup_continue() is provided where other
> > callers would use dentry_lookup().  The call will fail if, after the
> > lock was gained, the child is no longer a child of the given parent.
> > 
> > There are a couple of callers that want to lock a dentry in whatever
> > its current parent is.  For these a NULL parent can be passed, in which
> > case ->d_parent is used.  In this case the call cannot fail.
> > 
> > The idea behind the name is that the actual lookup occurred some time
> > ago, and now we are continuing with an operation on the dentry.
> > 
> > When the operation completes done_dentry_lookup() must be called.  An
> > extra reference is taken when the dentry_lookup_continue() call succeeds
> > and will be dropped by done_dentry_lookup().
> > 
> > This will be used in smb/server, ecryptfs, and overlayfs, each of which
> > have their own lock_parent() or parent_lock() or similar; and a few
> > other places which lock the parent but don't check if the parent is
> > still correct (often because rename isn't supported so parent cannot be
> > incorrect).
> 
> I would really like the see the conversion of these callers.  You are
> asking for a buy-in for a primitive with specific semantics; that's
> hard to review without seeing how it will be used.
> 

All, or just some?
I use dentry_lookup_continue() in:
  cachefiles: 4 times
  ecryptfs: once
  overlayfs: twice
  smb/server: once
  apparmor: once

Maybe I could include all in the one patch...

NeilBrown