From: Trond Myklebust Subject: RE: [PATCH 1/1] nfs: fix race between renewd, umount, and the state manager in V4.1 Date: Fri, 22 Jan 2010 14:41:38 -0500 Message-ID: <1264189298.30757.16.camel@localhost> References: <1264135871-13083-1-git-send-email-batsakis@netapp.com> <1264186039.30757.7.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: linux-nfs@vger.kernel.org To: "Batsakis, Alexandros" Return-path: Received: from mx2.netapp.com ([216.240.18.37]:64524 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752813Ab0AVTlj convert rfc822-to-8bit (ORCPT ); Fri, 22 Jan 2010 14:41:39 -0500 Received: from svlrsexc1-prd.hq.netapp.com (svlrsexc1-prd.hq.netapp.com [10.57.115.30]) by smtp2.corp.netapp.com (8.13.1/8.13.1/NTAP-1.6) with ESMTP id o0MJfdbF019762 for ; Fri, 22 Jan 2010 11:41:39 -0800 (PST) In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, 2010-01-22 at 11:30 -0800, Batsakis, Alexandros wrote: > > > -----Original Message----- > > From: Myklebust, Trond > > Sent: Friday, January 22, 2010 10:47 AM > > To: Batsakis, Alexandros > > Cc: linux-nfs@vger.kernel.org; Myklebust, Trond > > Subject: Re: [PATCH 1/1] nfs: fix race between renewd, umount, and the > > state manager in V4.1 > > > > On Thu, 2010-01-21 at 20:51 -0800, Alexandros Batsakis wrote: > > > > > struct rpc_cred *nfs4_get_setclientid_cred(struct nfs_client *clp) > > > @@ -878,7 +888,11 @@ void nfs4_schedule_state_manager(struct > > nfs_client *clp) > > > if (test_and_set_bit(NFS4CLNT_MANAGER_RUNNING, &clp->cl_state) != > > 0) > > > return; > > > __module_get(THIS_MODULE); > > > - atomic_inc(&clp->cl_count); > > > + if (!atomic_inc_not_zero(&clp->cl_count)) { > > > + nfs4_clear_state_manager_bit(clp); > > > + module_put(THIS_MODULE); > > > + return; > > > + } > > > > The use of atomic_inc_not_zero() should not be necessary here. Anybody > > who is calling this function without holding a reference to clp is > > doing > > something fundamentally wrong. > > Agreed, but how can we enforce this (especially with asynchronous RPC) ? > For example what will happen if _during_ umount (after nfs_put_client()), an NFS call that was sleeping e.g. waiting for the server to come up, reaches the server and the response causes the state manager to start ? > Any ideas ? What would you expect to see running during umount? Nobody can be holding a reference to the vfsmount at that point, so there should be no active processes around to make NFS calls. Trond