Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 25 Oct 2019 11:21:19 -0400
From:   "J. Bruce Fields" <bfields@redhat.com>
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v2] nfsd: Fix races between nfsd4_cb_release() and
 nfsd4_shutdown_callback()
Message-ID: <20191025152119.GC16053@pick.fieldses.org>
References: <20191023214318.9350-1-trond.myklebust@hammerspace.com>
 <20191025145147.GA16053@pick.fieldses.org>
 <97f56de86f0aeafb56998023d0561bb4a6233eb8.camel@hammerspace.com>
MIME-Version: 1.0
In-Reply-To: <97f56de86f0aeafb56998023d0561bb4a6233eb8.camel@hammerspace.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Content-Type: text/plain; charset=WINDOWS-1252
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

On Fri, Oct 25, 2019 at 02:55:45PM +0000, Trond Myklebust wrote:
> On Fri, 2019-10-25 at 10:51 -0400, J. Bruce Fields wrote:
> > On Wed, Oct 23, 2019 at 05:43:18PM -0400, Trond Myklebust wrote:
> > > When we're destroying the client lease, and we call
> > > nfsd4_shutdown_callback(), we must ensure that we do not return
> > > before all outstanding callbacks have terminated and have
> > > released their payloads.
> >=20
> > This is great, thanks!  We've seen what I'm fairly sure is the same
> > bug
> > from Red Hat users.  I think my blind spot was an assumption that
> > rpc tasks wouldn't outlive rpc_shutdown_client().
> >=20
> > However, it's causing xfstests runs to hang, and I haven't worked out
> > why yet.
> >=20
> > I'll spend some time on it this afternoon and let you know what I
> > figure
> > out.
> >=20
>=20
> Is that happening with v2 or with v1? With v1 there is definitely a
> hang in __destroy_client() due to the refcount leak that I believe I
> fixed in v2.

I thought I was running v2, let me double-check....

--b.

>=20
> > --b.
> >=20
> > > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > > ---
> > > v2 - Fix a leak of clp->cl_cb_inflight when running null probes
> > >=20
> > >  fs/nfsd/nfs4callback.c | 97 +++++++++++++++++++++++++++++++++-----
> > > ----
> > >  fs/nfsd/state.h        |  1 +
> > >  2 files changed, 79 insertions(+), 19 deletions(-)
> > >=20
> > > diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
> > > index 524111420b48..a3c9517bcc64 100644
> > > --- a/fs/nfsd/nfs4callback.c
> > > +++ b/fs/nfsd/nfs4callback.c
> > > @@ -826,6 +826,31 @@ static int max_cb_time(struct net *net)
> > >  =09return max(nn->nfsd4_lease/10, (time_t)1) * HZ;
> > >  }
> > > =20
> > > +static struct workqueue_struct *callback_wq;
> > > +
> > > +static bool nfsd4_queue_cb(struct nfsd4_callback *cb)
> > > +{
> > > +=09return queue_work(callback_wq, &cb->cb_work);
> > > +}
> > > +
> > > +static void nfsd41_cb_inflight_begin(struct nfs4_client *clp)
> > > +{
> > > +=09atomic_inc(&clp->cl_cb_inflight);
> > > +}
> > > +
> > > +static void nfsd41_cb_inflight_end(struct nfs4_client *clp)
> > > +{
> > > +
> > > +=09if (atomic_dec_and_test(&clp->cl_cb_inflight))
> > > +=09=09wake_up_var(&clp->cl_cb_inflight);
> > > +}
> > > +
> > > +static void nfsd41_cb_inflight_wait_complete(struct nfs4_client
> > > *clp)
> > > +{
> > > +=09wait_var_event(&clp->cl_cb_inflight,
> > > +=09=09=09!atomic_read(&clp->cl_cb_inflight));
> > > +}
> > > +
> > >  static const struct cred *get_backchannel_cred(struct nfs4_client
> > > *clp, struct rpc_clnt *client, struct nfsd4_session *ses)
> > >  {
> > >  =09if (clp->cl_minorversion =3D=3D 0) {
> > > @@ -937,14 +962,21 @@ static void nfsd4_cb_probe_done(struct
> > > rpc_task *task, void *calldata)
> > >  =09=09clp->cl_cb_state =3D NFSD4_CB_UP;
> > >  }
> > > =20
> > > +static void nfsd4_cb_probe_release(void *calldata)
> > > +{
> > > +=09struct nfs4_client *clp =3D container_of(calldata, struct
> > > nfs4_client, cl_cb_null);
> > > +
> > > +=09nfsd41_cb_inflight_end(clp);
> > > +
> > > +}
> > > +
> > >  static const struct rpc_call_ops nfsd4_cb_probe_ops =3D {
> > >  =09/* XXX: release method to ensure we set the cb channel down if
> > >  =09 * necessary on early failure? */
> > >  =09.rpc_call_done =3D nfsd4_cb_probe_done,
> > > +=09.rpc_release =3D nfsd4_cb_probe_release,
> > >  };
> > > =20
> > > -static struct workqueue_struct *callback_wq;
> > > -
> > >  /*
> > >   * Poke the callback thread to process any updates to the callback
> > >   * parameters, and send a null probe.
> > > @@ -975,9 +1007,12 @@ void nfsd4_change_callback(struct nfs4_client
> > > *clp, struct nfs4_cb_conn *conn)
> > >   * If the slot is available, then mark it busy.  Otherwise, set
> > > the
> > >   * thread for sleeping on the callback RPC wait queue.
> > >   */
> > > -static bool nfsd41_cb_get_slot(struct nfs4_client *clp, struct
> > > rpc_task *task)
> > > +static bool nfsd41_cb_get_slot(struct nfsd4_callback *cb, struct
> > > rpc_task *task)
> > >  {
> > > -=09if (test_and_set_bit(0, &clp->cl_cb_slot_busy) !=3D 0) {
> > > +=09struct nfs4_client *clp =3D cb->cb_clp;
> > > +
> > > +=09if (!cb->cb_holds_slot &&
> > > +=09    test_and_set_bit(0, &clp->cl_cb_slot_busy) !=3D 0) {
> > >  =09=09rpc_sleep_on(&clp->cl_cb_waitq, task, NULL);
> > >  =09=09/* Race breaker */
> > >  =09=09if (test_and_set_bit(0, &clp->cl_cb_slot_busy) !=3D 0) {
> > > @@ -985,10 +1020,32 @@ static bool nfsd41_cb_get_slot(struct
> > > nfs4_client *clp, struct rpc_task *task)
> > >  =09=09=09return false;
> > >  =09=09}
> > >  =09=09rpc_wake_up_queued_task(&clp->cl_cb_waitq, task);
> > > +=09=09cb->cb_holds_slot =3D true;
> > >  =09}
> > >  =09return true;
> > >  }
> > > =20
> > > +static void nfsd41_cb_release_slot(struct nfsd4_callback *cb)
> > > +{
> > > +=09struct nfs4_client *clp =3D cb->cb_clp;
> > > +
> > > +=09if (cb->cb_holds_slot) {
> > > +=09=09cb->cb_holds_slot =3D false;
> > > +=09=09clear_bit(0, &clp->cl_cb_slot_busy);
> > > +=09=09rpc_wake_up_next(&clp->cl_cb_waitq);
> > > +=09}
> > > +}
> > > +
> > > +static void nfsd41_destroy_cb(struct nfsd4_callback *cb)
> > > +{
> > > +=09struct nfs4_client *clp =3D cb->cb_clp;
> > > +
> > > +=09nfsd41_cb_release_slot(cb);
> > > +=09if (cb->cb_ops && cb->cb_ops->release)
> > > +=09=09cb->cb_ops->release(cb);
> > > +=09nfsd41_cb_inflight_end(clp);
> > > +}
> > > +
> > >  /*
> > >   * TODO: cb_sequence should support referring call lists,
> > > cachethis, multiple
> > >   * slots, and mark callback channel down on communication errors.
> > > @@ -1005,11 +1062,8 @@ static void nfsd4_cb_prepare(struct rpc_task
> > > *task, void *calldata)
> > >  =09 */
> > >  =09cb->cb_seq_status =3D 1;
> > >  =09cb->cb_status =3D 0;
> > > -=09if (minorversion) {
> > > -=09=09if (!cb->cb_holds_slot && !nfsd41_cb_get_slot(clp,
> > > task))
> > > -=09=09=09return;
> > > -=09=09cb->cb_holds_slot =3D true;
> > > -=09}
> > > +=09if (minorversion && !nfsd41_cb_get_slot(cb, task))
> > > +=09=09return;
> > >  =09rpc_call_start(task);
> > >  }
> > > =20
> > > @@ -1076,9 +1130,7 @@ static bool nfsd4_cb_sequence_done(struct
> > > rpc_task *task, struct nfsd4_callback
> > >  =09=09=09cb->cb_seq_status);
> > >  =09}
> > > =20
> > > -=09cb->cb_holds_slot =3D false;
> > > -=09clear_bit(0, &clp->cl_cb_slot_busy);
> > > -=09rpc_wake_up_next(&clp->cl_cb_waitq);
> > > +=09nfsd41_cb_release_slot(cb);
> > >  =09dprintk("%s: freed slot, new seqid=3D%d\n", __func__,
> > >  =09=09clp->cl_cb_session->se_cb_seq_nr);
> > > =20
> > > @@ -1091,8 +1143,10 @@ static bool nfsd4_cb_sequence_done(struct
> > > rpc_task *task, struct nfsd4_callback
> > >  =09=09ret =3D false;
> > >  =09goto out;
> > >  need_restart:
> > > -=09task->tk_status =3D 0;
> > > -=09cb->cb_need_restart =3D true;
> > > +=09if (!test_bit(NFSD4_CLIENT_CB_KILL, &clp->cl_flags)) {
> > > +=09=09task->tk_status =3D 0;
> > > +=09=09cb->cb_need_restart =3D true;
> > > +=09}
> > >  =09return false;
> > >  }
> > > =20
> > > @@ -1134,9 +1188,9 @@ static void nfsd4_cb_release(void *calldata)
> > >  =09struct nfsd4_callback *cb =3D calldata;
> > > =20
> > >  =09if (cb->cb_need_restart)
> > > -=09=09nfsd4_run_cb(cb);
> > > +=09=09nfsd4_queue_cb(cb);
> > >  =09else
> > > -=09=09cb->cb_ops->release(cb);
> > > +=09=09nfsd41_destroy_cb(cb);
> > > =20
> > >  }
> > > =20
> > > @@ -1170,6 +1224,7 @@ void nfsd4_shutdown_callback(struct
> > > nfs4_client *clp)
> > >  =09 */
> > >  =09nfsd4_run_cb(&clp->cl_cb_null);
> > >  =09flush_workqueue(callback_wq);
> > > +=09nfsd41_cb_inflight_wait_complete(clp);
> > >  }
> > > =20
> > >  /* requires cl_lock: */
> > > @@ -1255,8 +1310,7 @@ nfsd4_run_cb_work(struct work_struct *work)
> > >  =09clnt =3D clp->cl_cb_client;
> > >  =09if (!clnt) {
> > >  =09=09/* Callback channel broken, or client killed; give up:
> > > */
> > > -=09=09if (cb->cb_ops && cb->cb_ops->release)
> > > -=09=09=09cb->cb_ops->release(cb);
> > > +=09=09nfsd41_destroy_cb(cb);
> > >  =09=09return;
> > >  =09}
> > > =20
> > > @@ -1265,6 +1319,7 @@ nfsd4_run_cb_work(struct work_struct *work)
> > >  =09 */
> > >  =09if (!cb->cb_ops && clp->cl_minorversion) {
> > >  =09=09clp->cl_cb_state =3D NFSD4_CB_UP;
> > > +=09=09nfsd41_destroy_cb(cb);
> > >  =09=09return;
> > >  =09}
> > > =20
> > > @@ -1290,5 +1345,9 @@ void nfsd4_init_cb(struct nfsd4_callback *cb,
> > > struct nfs4_client *clp,
> > > =20
> > >  void nfsd4_run_cb(struct nfsd4_callback *cb)
> > >  {
> > > -=09queue_work(callback_wq, &cb->cb_work);
> > > +=09struct nfs4_client *clp =3D cb->cb_clp;
> > > +
> > > +=09nfsd41_cb_inflight_begin(clp);
> > > +=09if (!nfsd4_queue_cb(cb))
> > > +=09=09nfsd41_cb_inflight_end(clp);
> > >  }
> > > diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> > > index 46f56afb6cb8..d61b83b9654c 100644
> > > --- a/fs/nfsd/state.h
> > > +++ b/fs/nfsd/state.h
> > > @@ -367,6 +367,7 @@ struct nfs4_client {
> > >  =09struct net=09=09*net;
> > >  =09struct list_head=09async_copies;=09/* list of async copies */
> > >  =09spinlock_t=09=09async_lock;=09/* lock for async copies */
> > > +=09atomic_t=09=09cl_cb_inflight;=09/* Outstanding callbacks */
> > >  };
> > > =20
> > >  /* struct nfs4_client_reset
> > > --=20
> > > 2.21.0
> > >=20
> --=20
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>=20
>=20