From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stanislav Kinsbursky Subject: Re: [PATCH v2 1/4] SUNRPC: release per-net clients lock before calling PipeFS dentries creation Date: Mon, 27 Feb 2012 20:55:12 +0400 Message-ID: <4F4BB570.60105@parallels.com> References: <20120227154713.7941.17963.stgit@localhost6.localdomain6> <20120227155055.7941.18741.stgit@localhost6.localdomain6> <1330359695.5541.45.camel@lade.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE 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" To: "Myklebust, Trond" Return-path: In-Reply-To: <1330359695.5541.45.camel@lade.trondhjem.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 27.02.2012 20:21, Myklebust, Trond =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote: >> Lockdep is sad otherwise, because inode mutex is taken on PipeFS den= try >> 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 *c= lnt) >> struct sunrpc_net *sn =3D net_generic(clnt->cl_xprt->xprt_net, su= nrpc_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_bl= ock *nb, unsigned long event, >> void *ptr) >> { >> struct super_block *sb =3D ptr; >> - struct rpc_clnt *clnt; >> + struct rpc_clnt *clnt, *tmp; >> int error =3D 0; >> struct sunrpc_net *sn =3D net_generic(sb->s_fs_info, sunrpc_net_i= d); >> >> 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 =3D __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 =3D=3D RPC_PIPEFS_MOUNT) && clnt->cl_dentry) || (event =3D=3D RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry)) continue; atomic_inc(&clnt->cl_count); spin_unlock(&sn->rpc_client_lock); error =3D __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); --=20 Best regards, Stanislav Kinsbursky