On Tue, Jul 19, 2011 at 04:56:51PM -0700, Linus Torvalds wrote:
> On Tue, Jul 19, 2011 at 4:45 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > You know what... ?I doubt that you want to mess with ->d_seq checks here.
> 
> I'm ok with doing just the "move *inode setting" patch.
> 
> And if we really don't even allow renames of those mounted things, I
> guess the sequence number isn't required.

See vfs_rename_{dir,other}:

        error = -EBUSY;
        if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
                goto out;

in both, before even trying to call the method.  Traditional on all
Unices I've ever seen...