Re: [RFC PATCH] ocfs2: don't depend on DCACHE_DISCONNECTED

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Aug 02, 2012 at 12:57:44AM -0700, Joel Becker wrote:
> On Tue, Jul 31, 2012 at 06:33:23PM -0400, J. Bruce Fields wrote:
> > From: "J. Bruce Fields" <bfields@redhat.com>
> > 
> > XXX: I don't understand this code, but I also can't see how it can be
> > right as is: a dentry marked DCACHE_DISCONNECTED can in fact be a
> > fully-connected member of the dcache.  Is IS_ROOT() the right check
> > instead?
> > 
> > Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> 
> NAK.  DISCONNECTED is cleared when the dentry is materialized.

Are you sure?  ocfs2 uses d_splice_alias in its lookup method, which
doesn't clear DISCONNECTED.

(d_materialise_unique does something similar to d_splice_alias and also
clears DISCONNECTED.  However, I'm almost certain that's a bug in
d_materialise_unique.  The export code connects a
looked-up-by-filehandle directory by doing lookups in parents one step
at a time up to the root, only clearing DISCONNECTED once we know that
the dentry is connected all the way up to the root.  Clearing
DISCONNECTED as soon as a single dentry is connected to parents will
lead to bugs.)

> Here's the context.  When an ocfs2 dentry is discoverable via the tree
> (lookup or splicing an alias), we hold a cluster lock (the "dentry
> lock").  This is why we override d_move(), to make sure that state is
> kept sane.  That way, other nodes can communicate unlink to this node.

Alas, I'm not following you.  I'll stare at some of the code and try to
understand....

> They notify our node via the locking system, which does a
> d_delete()+dput(), which sets DISCONNECTED.  When the dentry gets its
> final put, we can properly accept an empty lock.

So you also depend on d_kill setting DISCONNECTED, huh.

--b.