Return-Path: Received: from mail.tpi.com ([70.99.223.143]:4625 "EHLO mail.tpi.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751844Ab0IAVLe (ORCPT ); Wed, 1 Sep 2010 17:11:34 -0400 Message-ID: <4C7EC17B.6070509@canonical.com> Date: Wed, 01 Sep 2010 15:11:23 -0600 From: Tim Gardner Reply-To: tim.gardner@canonical.com To: Neil Brown CC: "J. Bruce Fields" , linux-nfs@vger.kernel.org, "linux-kernel@vger.kernel.org" , Trond.Myklebust@netapp.com Subject: Re: nfsd deadlock, 2.6.36-rc3 References: <4C7E73CB.7030603@canonical.com> <20100901165400.GB1201@fieldses.org> <20100902065551.079e297c@notabene> In-Reply-To: <20100902065551.079e297c@notabene> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On 09/01/2010 02:55 PM, Neil Brown wrote: > On Wed, 1 Sep 2010 12:54:01 -0400 > "J. Bruce Fields" wrote: > >> On Wed, Sep 01, 2010 at 09:39:55AM -0600, Tim Gardner wrote: >>> I've been pursuing a simple reproducer for an NFS lockup that shows >>> up under stress. There is a bunch of info (some of it extraneous) in >>> http://bugs.launchpad.net/bugs/561210. I can reproduce it by writing >>> loop mounted NFS exports: >>> >>> /etc/fstab: 127.0.0.1:/srv /mnt/srv nfs rw 0 2 >>> /etc/exports: /srv 127.0.0.1(rw,insecure,no_subtree_check) >>> >>> See the attached scripts test_master.sh and test_client.sh. I simply >>> repeat './test_master.sh wait' until nfsd locks up, typically within >>> 1-3 cycles, e.g., >> >> Without looking at the dmesg and scripts carefully to confirm, one >> possible explanation is a deadlock when the server can't allocate memory >> required to service client requests, memory which the client itself >> needs to free by writing back dirty pages, but can't because the server >> isn't processing its writes. > > Having looked closely I'd say it is almost certainly this issue. > nfsd thread 1266 is in zone_reclaim waiting on a page to be written out so > the memory can be reused. > The other nfsd threads are blocking on a mutex held by 1266. > The dd processes are waiting for pages to be written to the server > > The particular page that 1266 is waiting on is almost certainly a page on an > NFS file, so you have a cyclic deadlock. > >> >> For that reason we just don't support loopback mounts--they're OK for >> light testing, but it would be difficult to make them completely robust >> under load. > > I wonder if we could use 'containers' to partition available memory between > 'nfsd threads' and 'everything else'?? Probably not worth the effort. > > NeilBrown > I'm currently working with my support folks to reproduce this using the exact same configuration as the customer, e.g., an NFS server (running as a guest on a VMWare ESX host) serving multiple gigabit clients. I assume that is a reasonable scenario? rtg -- Tim Gardner tim.gardner@canonical.com