Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx12.netapp.com ([216.240.18.77]:46706 "EHLO mx12.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753622Ab3KYUVH convert rfc822-to-8bit (ORCPT ); Mon, 25 Nov 2013 15:21:07 -0500 From: "Myklebust, Trond" To: "Adamson, Andy" CC: Linux NFS Mailing List Subject: Re: [PATCH 1/1] NFSv4.1 fix a kswap nfs4_state_manger race Date: Mon, 25 Nov 2013 20:20:57 +0000 Message-ID: References: <1385402270-14284-1-git-send-email-andros@netapp.com> <1385402270-14284-2-git-send-email-andros@netapp.com> <5B8C7A9D-CD9E-487A-AC62-B1292649835D@netapp.com> <496E7DBC-183B-43A2-91D4-837FC092E88A@netapp.com> <676D25D8-B845-42BC-BB1E-6441B6B8E5E3@netapp.com> <5BE68579-3F17-4786-89B9-21CEC1A94E8E@netapp.com> <48468258-591E-49A8-9EAA-2DD8E3993100@netapp.com> In-Reply-To: <48468258-591E-49A8-9EAA-2DD8E3993100@netapp.com> Content-Type: text/plain; charset="Windows-1252" MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Nov 25, 2013, at 15:10, Adamson, Andy wrote: > > On Nov 25, 2013, at 2:53 PM, "Myklebust, Trond" > wrote: > >> >> On Nov 25, 2013, at 14:27, Adamson, Andy wrote: >> >>> >>> On Nov 25, 2013, at 1:33 PM, "Myklebust, Trond" >>> wrote: >>> >>>> >>>> On Nov 25, 2013, at 13:13, Myklebust, Trond wrote: >>>> >>>>> >>>>> On Nov 25, 2013, at 12:57, wrote: >>>>> >>>>>> From: Andy Adamson >>>>>> >>>>>> The state manager is recovering expired state and recovery OPENs are being >>>>>> processed. If kswapd is pruning inodes at the same time, a deadlock can occur >>>>>> when kswapd calls evict_inode on an NFSv4.1 inode with a layout, and the >>>>>> resultant layoutreturn gets an error that the state mangager is to handle, >>>>>> causing the layoutreturn to wait on the (NFS client) cl_rpcwaitq. >>>>>> >>>>>> At the same time an open is waiting for the inode deletion to complete in >>>>>> __wait_on_freeing_inode. >>>>>> >>>>>> If the open is either the open called by the state manager, or an open from >>>>>> the same open owner that is holding the NFSv4.0 sequence id which causes the >>>>>> OPEN from the state manager to wait for the sequence id on the Seqid_waitqueue, >>>>>> then the state is deadlocked with kswapd. >>>>>> >>>>>> Do not handle LAYOUTRETURN errors when called from nfs4_evict_inode. >>>>> >>>>> Why are we waiting for recovery in LAYOUTRETURN at all? Layouts are automatically lost when the server reboots or when the lease is otherwise lost. >>>>> >>>>> IOW: Is there any reason why we need to special-case nfs4_evict_inode? Shouldn?t we just bail out on error in _all_ cases? >>>> >>>> BTW: Is it possible that we might have a similar problem with delegreturn? That too can be called from nfs4_evict_inode? >>> >>> Yes, good point. kswapd could be waiting for a delegation to return which has an error along with the same scenario with sys_open and the state manager running. >>> >>> With delegreturn, we most definately want to limit 'no error handling' to the evict inode case. >> >> Ah? I forgot that the delegreturn in nfs4_evict_inode is asynchronous and doesn?t wait for completion, so it shouldn?t be a problem here. > > Except we just changed that to fix a different state manager hang: > > commit 4a82fd7c4e78a1b7a224f9ae8bb7e1fd95f670e0 > Author: Andy Adamson > Date: Fri Nov 15 16:36:16 2013 -0500 > > NFSv4 wait on recovery for async session errors Right, but that won?t prevent nfs4_evict_inode from completing, and hence the OPEN that is waiting in nfs_fhget() can also complete, and so there is no deadlock with the state manager thread. Cheers Trond -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com