Re: find_fh_dentry returned a DISCONNECTED directory

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

On Thu, Feb 13, 2014 at 08:25:43PM -0800, Eric W. Biederman wrote:
> "J. Bruce Fields" <bfields@fieldses.org> writes:
> 
> > On Thu, Feb 13, 2014 at 03:45:16PM -0800, Eric W. Biederman wrote:
> >> "J. Bruce Fields" <bfields@fieldses.org> writes:
> >> 
> >> > Yesterday you passed on a report of this printk from nfsdfh.c firing:
> >> >
> >> > 	printk("nfsd: find_fh_dentry returned a DISCONNECTED directory: %pd2\n",
> >> > 	                                dentry);
> >> >
> >> > I think the dentry probably comes from the FILEID_ROOT case of:
> >> >
> >> > 	if (fileid_type == FILEID_ROOT)
> >> > 		dentry = dget(exp->ex_path.dentry);
> >> > 	else {
> >> > 		dentry = exportfs_decode_fh(exp->ex_path.mnt, fid,
> >> > 				data_left, fileid_type,
> >> > 				nfsd_acceptable, exp);
> >> >         }
> >> >
> >> > In that case the dentry was found using ordinary filesystem lookups, so
> >> > doesn't go through the same DISCONNECTED-clearing logic as in the case
> >> > of lookups by filehandle.
> >> >
> >> > Probably they have an export root that's not a filesystem root, and the
> >> > lookups happened in the right order?
> >> >
> >> > I suspect that's fine, and that the printk is just stupid, but maybe we
> >> > should clear DISCONNECTED when possible on normal lookups.  The
> >> > following is my attempt, though I'm not sure if d_alloc is the right
> >> > place to do this.  In any case it might help confirm this is what's
> >> > happening.
> >> >
> >> > So if you pass along this patch to the person who was seeing that printk
> >> > I'd be interested in the results.
> >> 
> >> I have been reading through the dentry code for other reasons and your
> >> patch definitely won't change anything. __d_alloc sets d_flags = 0.
> >> Therefore d_alloc always returns with d_flags == 0.
> >
> > You're right, of course.  I wasn't thinking straight.
> >
> > So the only dentries with DISCONNECTED set are those created with
> > d_obtain_alias, which is normally only used when you're looking up by
> > filehandle.
> >
> > Except btrfs has a weird use in get_default_root().  So maybe they were
> > running into the dentry that created?
> >
> > So btrfs should probably be using something else, I'm not sure what.
> 
> The nfs client also has the case where it uses DISCONNECTED dentries for
> directories that are not root on the server.  Which seems very similiar
> to the btrfs case.

I don't think there's any reason for those to be flagged DISCONNECTED
either.

--b.

> 
> Usually I would expect some of these things to pass through
> d_materialise_unique and become connected.  But I don't know much about
> the nfsd usage and how things connected.
> 
> Eric
>