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
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