From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754129Ab2B0RhT (ORCPT ); Mon, 27 Feb 2012 12:37:19 -0500 Received: from mx2.netapp.com ([216.240.18.37]:1746 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753715Ab2B0RhR (ORCPT ); Mon, 27 Feb 2012 12:37:17 -0500 X-IronPort-AV: E=Sophos;i="4.73,491,1325491200"; d="scan'208";a="628913105" From: "Myklebust, Trond" To: Stanislav Kinsbursky CC: "linux-nfs@vger.kernel.org" , Pavel Emelianov , "neilb@suse.de" , "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "James Bottomley" , "bfields@fieldses.org" , "davem@davemloft.net" , "devel@openvz.org" Subject: Re: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation Thread-Topic: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation Thread-Index: AQHM9Weod0HJbXoOhkm4LDxKtXHHipZQ9otygACRqQA= Date: Mon, 27 Feb 2012 17:37:13 +0000 Message-ID: <1330364238.5541.52.camel@lade.trondhjem.org> References: <20120227154713.7941.17963.stgit@localhost6.localdomain6> <20120227155055.7941.18741.stgit@localhost6.localdomain6> <1330359695.5541.45.camel@lade.trondhjem.org> <4F4BB570.60105@parallels.com> In-Reply-To: <4F4BB570.60105@parallels.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.104.60.115] Content-Type: text/plain; charset="utf-8" Content-ID: MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id q1RHbPhd019729 On Mon, 2012-02-27 at 20:55 +0400, Stanislav Kinsbursky wrote: > 27.02.2012 20:21, Myklebust, Trond пишет: > > On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote: > >> Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry > >> creation, which can be called on mount notification, where this per-net client > >> lock is taken on clients list walk. > >> > >> Signed-off-by: Stanislav Kinsbursky > >> > >> --- > >> net/sunrpc/clnt.c | 10 +++++++--- > >> 1 files changed, 7 insertions(+), 3 deletions(-) > >> > >> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c > >> index bb7ed2f3..ddb5741 100644 > >> --- a/net/sunrpc/clnt.c > >> +++ b/net/sunrpc/clnt.c > >> @@ -84,7 +84,7 @@ static void rpc_register_client(struct rpc_clnt *clnt) > >> struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id); > >> > >> spin_lock(&sn->rpc_client_lock); > >> - list_add(&clnt->cl_clients,&sn->all_clients); > >> + list_add_tail(&clnt->cl_clients,&sn->all_clients); > >> spin_unlock(&sn->rpc_client_lock); > >> } > >> > >> @@ -208,15 +208,19 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event, > >> void *ptr) > >> { > >> struct super_block *sb = ptr; > >> - struct rpc_clnt *clnt; > >> + struct rpc_clnt *clnt, *tmp; > >> int error = 0; > >> struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id); > >> > >> spin_lock(&sn->rpc_client_lock); > >> - list_for_each_entry(clnt,&sn->all_clients, cl_clients) { > >> + list_for_each_entry_safe(clnt, tmp,&sn->all_clients, cl_clients) { > >> + atomic_inc(&clnt->cl_count); > >> + spin_unlock(&sn->rpc_client_lock); > >> error = __rpc_pipefs_event(clnt, event, sb); > >> + rpc_release_client(clnt); > >> if (error) > >> break; > >> + spin_lock(&sn->rpc_client_lock); > >> } > >> spin_unlock(&sn->rpc_client_lock); > >> return error; > >> > > > > This won't be safe. Nothing guarantees that 'tmp' remains valid after > > you drop the spin_lock. > > > > I think you rather need to add a check for whether clnt->cl_dentry is in > > the right state (NULL if RPC_PIPEFS_UMOUNT or non-NULL if > > RPC_PIPEFS_MOUNT) before deciding whether or not to atomic_inc() and > > drop the lock, so that you can restart the loop after calling > > __rpc_pipefs_event(). > > > > Gmmm. > Please, correct me, if I'm wrong, that you are proposing something like this: > > spin_lock(&sn->rpc_client_lock); > again: > list_for_each_entry(clnt,&sn->all_clients, cl_clients) { > if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) || > (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry)) > continue; > atomic_inc(&clnt->cl_count); > spin_unlock(&sn->rpc_client_lock); > error = __rpc_pipefs_event(clnt, event, sb); > rpc_release_client(clnt); > spin_lock(&sn->rpc_client_lock); > if (error) > break; > goto again; > } > spin_unlock(&sn->rpc_client_lock); Something along those lines, yes... Alternatively, you could do as David proposes, and grab a reference to the next rpc_client before calling rpc_release_client. Either works for me... -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I