From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F41FFFA372C for ; Fri, 8 Nov 2019 16:48:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D14B82178F for ; Fri, 8 Nov 2019 16:48:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728156AbfKHQsC (ORCPT ); Fri, 8 Nov 2019 11:48:02 -0500 Received: from mx2.suse.de ([195.135.220.15]:41350 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726036AbfKHQsC (ORCPT ); Fri, 8 Nov 2019 11:48:02 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id ACEABAE7F; Fri, 8 Nov 2019 16:47:59 +0000 (UTC) Date: Fri, 8 Nov 2019 16:47:58 +0000 From: Luis Henriques To: Ilya Dryomov Cc: Jeff Layton , Sage Weil , "Yan, Zheng" , Ceph Development , LKML Subject: Re: [RFC PATCH 0/2] ceph: safely use 'copy-from' Op on Octopus OSDs Message-ID: <20191108164758.GA1760@hermes.olymp> References: <20191108141555.31176-1-lhenriques@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 08, 2019 at 04:15:35PM +0100, Ilya Dryomov wrote: > On Fri, Nov 8, 2019 at 3:15 PM Luis Henriques wrote: > > > > Hi! > > > > (Sorry for the long cover letter!) > > This is exactly what cover letters are for! > > > > > Since the fix for [1] has finally been merged and should be available in > > the next (Octopus) ceph release, I'm trying to clean-up my kernel client > > patch that tries to find out whether or not it's safe to use the > > 'copy-from' RADOS operation for copy_file_range. > > > > So, the fix for [1] was to modify the 'copy-from' operation to allow > > clients to optionally (using the CEPH_OSD_COPY_FROM_FLAG_TRUNCATE_SEQ > > flag) send the extra truncate_seq and truncate_size parameters. Since > > only Octopus will have this fix (no backports planned), the client > > simply needs to ensure the OSDs being used have SERVER_OCTOPUS in their > > features. > > > > My initial solution was to add an extra test in __submit_request, > > looping all the request ops and checking if the connection has the > > required features for that operation. Obviously, at the moment only the > > copy-from operation has a restriction but I guess others may be added in > > the future. I believe that doing this at this point (__submit_request) > > allows to cover cases where a cluster is being upgraded to Octopus and > > we have different OSDs running with different feature bits. > > > > Unfortunately, this solution is racy because the connection state > > machine may be changing and the peer_features field isn't yet set. For > > example: if the connection to an OSD is being re-open when we're about > > to check the features, the con->state will be CON_STATE_PREOPEN and the > > con->peer_features will be 0. I tried to find ways to move the feature > > check further down in the stack, but that can't be easily done without > > adding more infrastructure. A solution that came to my mind was to add > > a new con->ops, invoked in the context of ceph_con_workfn, under the > > con->mutex. This callback could then verify the available features, > > aborting the operation if needed. > > > > Note that the race in this patchset doesn't seem to be a huge problem, > > other than occasionally reverting to a VFS generic copy_file_range, as > > -EOPNOTSUPP will be returned here. But it's still a race, and there are > > probably other cases that I'm missing. > > > > Anyway, maybe I'm missing an obvious solution for checking these OSD > > features, but I'm open to any suggestions on other options (or some > > feedback on the new callback in ceph_connection_operations option). > > > > [1] https://tracker.ceph.com/issues/37378 > > If the OSD checked for unknown flags, like newer syscalls do, it would > be super easy, but it looks like it doesn't. > > An obvious solution is to look at require_osd_release in osdmap, but we > don't decode that in the kernel because it lives the OSD portion of the > osdmap. We could add that and consider the fact that the client now > needs to decode more than just the client portion a design mistake. > I'm not sure what can of worms does that open and if copy-from alone is > worth it though. Perhaps that field could be moved to (or a copy of it > be replicated in) the client portion of the osdmap starting with > octopus? We seem to be running into it on the client side more and > more... I can't say I'm thrilled with the idea of going back to hack into the OSDs code again, I was hoping to be able to handle this with the information we already have on the connection peer_features field. It took me *months* to have the OSD fix merged in so I'm not really convinced a change to the osdmap would make it into Octopus :-) (But I'll have a look at this and see if I can understand what moving or replicating the field in the osdmap would really entail.) > Given the track record of this feature (the fix for the most recently > discovered data corrupting bug hasn't even merged yet), I would be very > hesitant to turn it back on by default even if we figure out a good > solution for the feature check. In my opinion, it should stay opt-in. Ok, makes sense. And thanks a lot for your feedback, Ilya. Cheers, -- Luís