On Fri, 2017-12-01 at 08:10 -0500, Scott Mayhew wrote: > 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(cl > > > p, > > > result, cred); > > > nfs_wait_client_init_comp > > > lete > > > (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 <smayhew@xxxxxxxxxx> > > > --- > > > 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. > Wouldn't that mean you would end up with different behaviour for NFSv4 and NFSv4.1 w.r.t. trunking, with the former observing the current behaviour, and only the latter working correctly? -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@xxxxxxxxxxxxxxx ��.n��������+%������w��{.n�����{��w���jg��������ݢj����G�������j:+v���w�m������w�������h�����٥