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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 38749C11F66 for ; Thu, 1 Jul 2021 01:16:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1D487613FC for ; Thu, 1 Jul 2021 01:16:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238377AbhGABTH (ORCPT ); Wed, 30 Jun 2021 21:19:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56792 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238345AbhGABTG (ORCPT ); Wed, 30 Jun 2021 21:19:06 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F01AEC061756 for ; Wed, 30 Jun 2021 18:16:36 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id 06CF664B9; Wed, 30 Jun 2021 21:16:36 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 06CF664B9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1625102196; bh=lyUDbKpbLFmhewN8r6SRIQ/4QCIfARc+Hng2U9QM4Uo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DL+UChtaLYRRVCY+5We3f8+UHLVQQPCTG3VUIDgPKwqD4l/hn0VDwyyNR9OfNe7qc OhFyMOc/4E1PTy3Z8tZvhblsaoNW7n6IbUJ1FaXOzRWuicddRY168UsiaVcJ5hlMXR aYk2+mXYjZFBjF+NsB5OWhO9M/Td5hAey7V0yAX8= Date: Wed, 30 Jun 2021 21:16:36 -0400 From: "J. Bruce Fields" To: dai.ngo@oracle.com Cc: chuck.lever@oracle.com, linux-nfs@vger.kernel.org Subject: Re: [PATCH RFC 1/1] nfsd: Initial implementation of NFSv4 Courteous Server Message-ID: <20210701011636.GI20229@fieldses.org> References: <20210603181438.109851-1-dai.ngo@oracle.com> <20210628202331.GC6776@fieldses.org> <9628be9d-2bfd-d036-2308-847cb4f1a14d@oracle.com> <20210630180527.GE20229@fieldses.org> <08caefcd-5271-8d44-326d-395399ff465c@oracle.com> <20210630185519.GG20229@fieldses.org> <08884534-931b-d828-0340-33c396674dd5@oracle.com> <20210630192429.GH20229@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Wed, Jun 30, 2021 at 04:48:57PM -0700, dai.ngo@oracle.com wrote: > > On 6/30/21 12:24 PM, J. Bruce Fields wrote: > >On Wed, Jun 30, 2021 at 12:13:35PM -0700, dai.ngo@oracle.com wrote: > >>On 6/30/21 11:55 AM, J. Bruce Fields wrote: > >>>On Wed, Jun 30, 2021 at 11:49:18AM -0700, dai.ngo@oracle.com wrote: > >>>>On 6/30/21 11:05 AM, J. Bruce Fields wrote: > >>>>>On Wed, Jun 30, 2021 at 10:51:27AM -0700, dai.ngo@oracle.com wrote: > >>>>>>>On 6/28/21 1:23 PM, J. Bruce Fields wrote: > >>>>>>>>where ->fl_expire_lock is a new lock callback with second > >>>>>>>>argument "check" > >>>>>>>>where: > >>>>>>>> > >>>>>>>>     check = 1 means: just check whether this lock could be freed > >>>>>>Why do we need this, is there a use case for it? can we just always try > >>>>>>to expire the lock and return success/fail? > >>>>>We can't expire the client while holding the flc_lock. And once we drop > >>>>>that lock we need to restart the loop. Clearly we can't do that every > >>>>>time. > >>>>> > >>>>>(So, my code was wrong, it should have been: > >>>>> > >>>>> > >>>>> if (fl->fl_lops->fl_expire_lock(fl, 1)) { > >>>>> spin_unlock(&ct->flc_lock); > >>>>> fl->fl_lops->fl_expire_locks(fl, 0); > >>>>> goto retry; > >>>>> } > >>>>> > >>>>>) > >>>>This is what I currently have: > >>>> > >>>>retry: > >>>> list_for_each_entry(fl, &ctx->flc_posix, fl_list) { > >>>> if (!posix_locks_conflict(request, fl)) > >>>> continue; > >>>> > >>>> if (fl->fl_lmops && fl->fl_lmops->lm_expire_lock) { > >>>> spin_unlock(&ctx->flc_lock); > >>>> ret = fl->fl_lmops->lm_expire_lock(fl, 0); > >>>> spin_lock(&ctx->flc_lock); > >>>> if (ret) > >>>> goto retry; > >>>We have to retry regardless of the return value. Once we've dropped > >>>flc_lock, it's not safe to continue trying to iterate through the list. > >>Yes, thanks! > >> > >>>> } > >>>> > >>>> if (conflock) > >>>> locks_copy_conflock(conflock, fl); > >>>> > >>>>>But the 1 and 0 cases are starting to look pretty different; maybe they > >>>>>should be two different callbacks. > >>>>why the case of 1 (test only) is needed, who would use this call? > >>>We need to avoid dropping the spinlock in the case there are no clients > >>>to expire, otherwise we'll make no forward progress. > >>I think we can remember the last checked file_lock and skip it: > >I doubt that works in the case there are multiple locks with > >lm_expire_lock set. > > > >If you really don't want another callback here, maybe you could set some > >kind of flag on the lock. > > > >At the time a client expires, you're going to have to walk all of its > >locks to see if anyone's waiting for them. At the same time maybe you > >could set an FL_EXPIRABLE flag on all those locks, and test for that > >here. > > > >If the network partition heals and the client comes back, you'd have to > >remember to clear that flag again. > > It's too much unnecessary work. > > Would this be suffice: > > retry: > list_for_each_entry(fl, &ctx->flc_posix, fl_list) { > if (!posix_locks_conflict(request, fl)) > continue; > if (fl->fl_lmops && fl->fl_lmops->lm_expire_lock && > fl->fl_lmops->lm_expire_lock(fl, 1)) { > spin_unlock(&ctx->flc_lock); > fl->fl_lmops->lm_expire_lock(fl, 0); > spin_lock(&ctx->flc_lock); > goto retry; > } > if (conflock) > locks_copy_conflock(conflock, fl); Looks OK to me.--b. > > -Dai > > > > >--b. > > > >>retry: > >> list_for_each_entry(fl, &ctx->flc_posix, fl_list) { > >> if (!posix_locks_conflict(request, fl)) > >> continue; > >> > >> if (checked_fl != fl && fl->fl_lmops && > >> fl->fl_lmops->lm_expire_lock) { > >> checked_fl = fl; > >> spin_unlock(&ctx->flc_lock); > >> fl->fl_lmops->lm_expire_lock(fl); > >> spin_lock(&ctx->flc_lock); > >> goto retry; > >> } > >> > >> if (conflock) > >> locks_copy_conflock(conflock, fl); > >> > >>-Dai > >> > >>>--b.