On Fri, 2012-11-30 at 02:00 +0000, Al Viro wrote:
> On Thu, Nov 29, 2012 at 05:54:02PM -0800, Patrick McLean wrote:
> > > Very interesting. Do you have anything mounted on the corresponding
> > > directories on server? The picture looks like you are getting empty
> > > fhandles in readdir+ respons for exactly the same directories that happen
> > > to be mountpoints on client. In any case, we shouldn't do that blind
> > > d_drop() - empty fhandles can happen. The only remaining question is
> > > why do they happen on that set of entries. From my reading of
> > > encode_entryplus_baggage() it looks like we have compose_entry_fh()
> > > failing for those entries and those entries alone. One possible cause
> > > would be d_mountpoint(dchild) being true on server. If it is true, we
> > > can declare the case closed; if not, I really wonder what's going on.
> >
> > Those directories do have the server's own copies of the said directories bind mounted at the moment in a separate mount namespace.
> >
> > Unmounting those directories on the server does appear to stop the WARN_ON from triggering.
>
> OK, that settles it. WARN_ON() and printks in the area can be dropped;
> the right fix is below. However, there's a similar place in cifs that
> also needs to be dealt with and I really, really wonder why the hell do
> we do d_drop() in nfs_revalidate_lookup(). It's not relevant in this
> bug, but I would like to understand what's wrong with simply returning
> 0 from ->d_revalidate() and letting the caller (in fs/namei.c) take care
> of unhashing, etc. itself. Would make have_submounts() in there pointless
> as well - we could just return 0 and let d_invalidate() take care of the
> checks... Trond?
The reason for the choice of d_drop over d_invalidate() is the d_count
checks. It really doesn't matter whether or not the client thinks it has
users for a directory if the server is telling you that it is ESTALE. So
we force a d_drop to prevent further lookups from finding it.
IOW: It is there in order to fix the case where the user does
'rmdir("foo"); mkdir("foo")' on the server.
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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