From: Trond Myklebust Subject: Re: [RFC][PATCH] client cannot get lock after other client got lock occur network partition. Date: Tue, 10 Nov 2009 21:35:49 +0900 Message-ID: <1257856550.3046.6.camel@heimdal.trondhjem.org> References: <4AF7DEAB.20202@cn.fujitsu.com> <1257772609.3754.11.camel@heimdal.trondhjem.org> <4AF934A1.9040908@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: NFSv3 list , "J. Bruce Fields" To: Mi Jinlong Return-path: Received: from mail-out2.uio.no ([129.240.10.58]:55715 "EHLO mail-out2.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756109AbZKJMfw (ORCPT ); Tue, 10 Nov 2009 07:35:52 -0500 In-Reply-To: <4AF934A1.9040908@cn.fujitsu.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, 2009-11-10 at 17:38 +0800, Mi Jinlong wrote: > Hi Trond >=20 > Trond Myklebust =E5=86=99=E9=81=93: > > On Mon, 2009-11-09 at 17:19 +0800, Mi Jinlong wrote: > >> Hi Trond et all > >> > >> There is a bug, when i test NFSv3 file's lock as followed: > >> > >> Step1: ClientA and ClientB open a same nfs file; > >> Step2: ClientA locks file with write lock, it's ok; > >> Step3: Cut off the network between ClientA and Server; > >> Step4: ClientB can not acquire for write lock successful forever, = even though > >> the network partition larger than NLM_HOST_EXPIRE. > >> > >> As i know, If use NFSv4, step4 can success after LEASE_TIME. > >> > >> Is it necessary to fix NFSv3 ?=20 > >> > >> The attached patch can make this case OK, but i am not sure it's g= ood. > >=20 > > Unfortunately, NLM (the NFSv2 and v3 locking protocol) is not lease > > based, so the above scenario is truly an unfixable one. > >=20 > > The problem with applying your patch is, in essence, that we risk > > breaking another scenario where a client grabs a lock, and then hol= ds it > > for a while. > > The reason this breaks is that there is no equivalent in the NLM > > protocol of the NFSv4 RENEW operation to tell the server that "This > > client is still alive and wants you to keep its state". >=20 > Thanks for your answer! >=20 > This bug seems serious, shouldn't we fix it? Unless you can think of a fix which works with the current NLM protocol= , I'd suggest simply encouraging people to move to a protocol with lease based locks: i.e. NFSv4... Cheers Trond