Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:47536 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933256AbaDIPU4 (ORCPT ); Wed, 9 Apr 2014 11:20:56 -0400 Date: Wed, 9 Apr 2014 11:20:55 -0400 From: Dr Fields James Bruce To: Trond Myklebust Cc: NFS Subject: Re: commit 1bc49d83c37c (nfsd4: fix nfs4err_resource in 4.1 case) Message-ID: <20140409152055.GB22938@fieldses.org> References: <20140409135625.GA22938@fieldses.org> <924781E0-38DB-4623-821C-4FB7C9AF52C8@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <924781E0-38DB-4623-821C-4FB7C9AF52C8@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Apr 09, 2014 at 10:12:58AM -0400, Trond Myklebust wrote: > > On Apr 9, 2014, at 9:56, Dr Fields James Bruce wrote: > > > On Wed, Apr 09, 2014 at 09:41:28AM -0400, Trond Myklebust wrote: > >> According to RFC5661, NFS4ERR_REP_TOO_BIG/NFS4ERR_REP_TOO_BIG_TO_CACHE > >> are only appropriate if "The reply to a Compound would exceed the > >> channel's negotiated maximum response size.”. Given that the callers > >> of nfsd4_encode_fattr appear to all pass in ‘buffer’ and ‘buflen’ > >> arguments that are limited to single page, doesn’t this mean that you > >> can end up returning nfs4err_resource in cases where > >> nfserr_rep_too_big/nfserr_rep_too_big_to_cache are simply not > >> appropriate? > > > > Yes, you're right. This will be fixed by later patches which remove > > those arbitrary single-page limits, but for now it's a bug. > > > > This was probably a bad way to sequence those patches. > > > > That said, all that patch is doing in those cases is replacing one > > useless error by another, so in practice I don't think reverting the > > patch would help anyone--so I'm inclined to leave this alone and wait > > for the real bug to be fixed (which is that we're imposing limits other > > than the session limits). > > > > Is this causing some problem right now? > > > > I’m not aware of any bug reports yet, but I did want to make sure that it was on your radar. > > That said, one immediate consequence of this patch will be that NFSv4.1 clients will now report EIO instead of EREMOTEIO if they hit the problem. That may make debugging a little less obvious. > Another consequence will be that if we ever do try to add client side handling of NFS4ERR_REP_TOO_BIG, then we now have to deal with the “handle existing buggy server” syndrome. Yeah, OK, I can see it would be annoying; maybe it's worth something like the following for 3.15? And then for 3.16 I'll delay this change till later in the xdr-encoding series. --b. commit a675223424673a6393fd291280af51fddd6a97ec Author: J. Bruce Fields Date: Wed Apr 9 11:07:01 2014 -0400 Revert "nfsd4: fix nfs4err_resource in 4.1 case" Since we're still limiting attributes to a page, the result here is that a large getattr result will return NFS4ERR_REP_TOO_BIG/TOO_BIG_TO_CACHE instead of NFS4ERR_RESOURCE. Both error returns are wrong, and the real bug here is the arbitrary limit on getattr results, fixed by as-yet out-of-tree patches. But at a minimum we can make life easier for clients by sticking to one broken behavior in released kernels instead of two.... Trond says: one immediate consequence of this patch will be that NFSv4.1 clients will now report EIO instead of EREMOTEIO if they hit the problem. That may make debugging a little less obvious. Another consequence will be that if we ever do try to add client side handling of NFS4ERR_REP_TOO_BIG, then we now have to deal with the “handle existing buggy server” syndrome. Reported-by: Trond Myklebust Signed-off-by: J. Bruce Fields diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 2723c1b..18881f3 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -3627,14 +3627,6 @@ nfsd4_encode_operation(struct nfsd4_compoundres *resp, struct nfsd4_op *op) /* nfsd4_check_resp_size guarantees enough room for error status */ if (!op->status) op->status = nfsd4_check_resp_size(resp, 0); - if (op->status == nfserr_resource && nfsd4_has_session(&resp->cstate)) { - struct nfsd4_slot *slot = resp->cstate.slot; - - if (slot->sl_flags & NFSD4_SLOT_CACHETHIS) - op->status = nfserr_rep_too_big_to_cache; - else - op->status = nfserr_rep_too_big; - } if (so) { so->so_replay.rp_status = op->status; so->so_replay.rp_buflen = (char *)resp->p - (char *)(statp+1);