[Ocfs2-devel] [RFC PATCH] ocfs2: don't depend on DCACHE_DISCONNECTED
J. Bruce Fields
bfields at fieldses.org
Thu Aug 2 05:59:10 PDT 2012
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 at 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 at 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.
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