Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:44647 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751874AbdLANKw (ORCPT ); Fri, 1 Dec 2017 08:10:52 -0500 Date: Fri, 1 Dec 2017 08:10:51 -0500 From: Scott Mayhew To: Trond Myklebust Cc: "anna.schumaker@netapp.com" , "linux-nfs@vger.kernel.org" Subject: Re: [PATCH v2] nfs: fix a deadlock in nfs client initialization Message-ID: <20171201131051.o2k56cej2iw7zih7@tonberry.usersys.redhat.com> References: <20171130144647.gwuchptqyiomcojl@tonberry.usersys.redhat.com> <20171130222135.3752-1-smayhew@redhat.com> <1512095773.27780.3.camel@primarydata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1512095773.27780.3.camel@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, 01 Dec 2017, Trond Myklebust wrote: > On Thu, 2017-11-30 at 17:21 -0500, Scott Mayhew wrote: > > The following deadlock can occur between a process waiting for a > > client > > to initialize in while walking the client list during nfsv4 server > > trunking > > detection and another process waiting for the nfs_clid_init_mutex so > > it > > can initialize that client: > > > > Process 1 Process 2 > > --------- --------- > > spin_lock(&nn->nfs_client_lock); > > list_add_tail(&CLIENTA->cl_share_link, > > &nn->nfs_client_list); > > spin_unlock(&nn->nfs_client_lock); > > spin_lock(&nn- > > >nfs_client_lock); > > list_add_tail(&CLIENTB- > > >cl_share_link, > > &nn- > > >nfs_client_list); > > spin_unlock(&nn- > > >nfs_client_lock); > > mutex_lock(&nfs_clid_init_mut > > ex); > > nfs41_walk_client_list(clp, > > result, cred); > > nfs_wait_client_init_complete > > (CLIENTA); > > (waiting for nfs_clid_init_mutex) > > > > Make sure nfs_match_client() only evaluates clients that have > > completed > > initialization in order to prevent that deadlock. > > > > Signed-off-by: Scott Mayhew > > --- > > fs/nfs/client.c | 11 +++++++++++ > > fs/nfs/nfs4client.c | 9 ++++++++- > > 2 files changed, 19 insertions(+), 1 deletion(-) > > > > diff --git a/fs/nfs/client.c b/fs/nfs/client.c > > index 0ac2fb1..7e42380 100644 > > --- a/fs/nfs/client.c > > +++ b/fs/nfs/client.c > > @@ -291,12 +291,23 @@ static struct nfs_client > > *nfs_match_client(const struct nfs_client_initdata *dat > > const struct sockaddr *sap = data->addr; > > struct nfs_net *nn = net_generic(data->net, nfs_net_id); > > > > +again: > > list_for_each_entry(clp, &nn->nfs_client_list, > > cl_share_link) { > > const struct sockaddr *clap = (struct sockaddr > > *)&clp->cl_addr; > > /* Don't match clients that failed to initialise > > properly */ > > if (clp->cl_cons_state < 0) > > continue; > > > > + /* If a client is still initializing then we need to > > wait */ > > + if (clp->cl_cons_state > NFS_CS_READY) { > > + spin_unlock(&nn->nfs_client_lock); > > + refcount_inc(&clp->cl_count); > > The refcount needs to be bumped before dropping the spinlock above. Okay. > > > + nfs_wait_client_init_complete(clp); > > + nfs_put_client(clp); > > + spin_lock(&nn->nfs_client_lock); > > + goto again; > > + } > > + > > /* Different NFS versions cannot share the same > > nfs_client */ > > if (clp->rpc_ops != data->nfs_mod->rpc_ops) > > continue; > > diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c > > index 12bbab0..39dd39c 100644 > > --- a/fs/nfs/nfs4client.c > > +++ b/fs/nfs/nfs4client.c > > @@ -411,8 +411,15 @@ struct nfs_client *nfs4_init_client(struct > > nfs_client *clp, > > if (error < 0) > > goto error; > > > > - if (clp != old) > > + if (clp != old) { > > clp->cl_preserve_clid = true; > > + /* > > + * Mark the client as having failed initialization > > so other > > + * processes walking the nfs_client_list in > > nfs_match_client() > > + * won't try to use it. > > + */ > > + nfs_mark_client_ready(clp, -EPERM); > > You can't do this if the client was already marked as NFS_CS_READY, so > you need at least to move the !nfs4_has_session() condition 4 lines > above this. How about if I change it to this: if (!nfs_client_init_is_complete(clp)) nfs_mark_client_ready(clp, -EPERM); In my earlier testing I had problems whenever I tried moving that !nfs4_has_session() condition. -Scott > > > + } > > nfs_put_client(clp); > > clear_bit(NFS_CS_TSM_POSSIBLE, &clp->cl_flags); > > return old; > -- > Trond Myklebust > Linux NFS client maintainer, PrimaryData > trond.myklebust@primarydata.com