Re: [pnfs] [PATCH 2/2] nfs41: fix state manager deadlock in session reset

Trond Myklebust
2009-11-12T13:46:47Z

On Thu, 2009-11-12 at 15:29 +0200, Benny Halevy wrote:
> On Nov. 11, 2009, 21:51 +0200, "William A. (Andy) Adamson" <androsadamson@gmail.com> wrote:
> > On Wed, Nov 11, 2009 at 2:20 PM, <andros@netapp.com> wrote:
> >> From: Andy Adamson <andros@netapp.com>
> >>
> >> If the session is reset during state recovery, the state manager thread can
> >> sleep on the slot_tbl_waitq causing a deadlock.
> >>
> >> Add a completion framework to the session. Have the state manager thread set
> >> a new session state (NFS4CLNT_SESSION_DRAINING) and wait for the session slot
> >> table to drain.
> >>
> >> Signal the state manager thread in nfs41_sequence_free_slot when the
> >> NFS4CLNT_SESSION_DRAINING bit is set and the session is drained.
> >>
> >> Reported-by: Trond Myklebust <trond@netapp.com>
> >> Signed-off-by: Andy Adamson <andros@netapp.com>
> >> ---
> >> fs/nfs/nfs4_fs.h | 1 +
> >> fs/nfs/nfs4proc.c | 25 ++++++++++++++++---------
> >> fs/nfs/nfs4state.c | 15 +++++++++++++++
> >> include/linux/nfs_fs_sb.h | 1 +
> >> 4 files changed, 33 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
> >> index 6ea07a3..e8604af 100644
> >> --- a/fs/nfs/nfs4_fs.h
> >> +++ b/fs/nfs/nfs4_fs.h
> >> @@ -45,6 +45,7 @@ enum nfs4_client_state {
> >> NFS4CLNT_RECLAIM_NOGRACE,
> >> NFS4CLNT_DELEGRETURN,
> >> NFS4CLNT_SESSION_SETUP,
> >> + NFS4CLNT_SESSION_DRAINING,
> >> };
> >>
> >> /*
> >> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> >> index 44d1c14..ebde948 100644
> >> --- a/fs/nfs/nfs4proc.c
> >> +++ b/fs/nfs/nfs4proc.c
> >> @@ -355,6 +355,16 @@ void nfs41_sequence_free_slot(const struct nfs_client *clp,
> >> }
> >> nfs4_free_slot(tbl, res->sr_slotid);
> >> res->sr_slotid = NFS4_MAX_SLOT_TABLE;
> >> +
> >> + /* Signal state manager thread if session is drained */
> >> + if (test_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state)) {
> >> + spin_lock(&tbl->slot_tbl_lock);
> >> + if (tbl->highest_used_slotid == -1) {
> >> + dprintk("%s COMPLETE: Session Drained\n", __func__);
> >> + complete(&clp->cl_session->complete);
> >> + }
> >> + spin_unlock(&tbl->slot_tbl_lock);
> >> + }
> >> }
> >>
> >> static void nfs41_sequence_done(struct nfs_client *clp,
> >> @@ -448,15 +458,11 @@ static int nfs41_setup_sequence(struct nfs4_session *session,
> >>
> >> spin_lock(&tbl->slot_tbl_lock);
> >> if (test_bit(NFS4CLNT_SESSION_SETUP, &session->clp->cl_state)) {
> >> - if (tbl->highest_used_slotid != -1) {
> >> - rpc_sleep_on(&tbl->slot_tbl_waitq, task, NULL);
> >> - spin_unlock(&tbl->slot_tbl_lock);
> >> - dprintk("<-- %s: Session reset: draining\n", __func__);
> >> - return -EAGAIN;
> >> - }
> >> -
> >> - /* The slot table is empty; start the reset thread */
> >> - dprintk("%s Session Reset\n", __func__);
> >> + /*
> >> + * The state manager will wait until the slot table is empty.
> >> + * Schedule the reset thread
> >> + */
> >> + dprintk("%s Schedule Session Reset\n", __func__);
> >> rpc_sleep_on(&tbl->slot_tbl_waitq, task, NULL);
> >> nfs4_schedule_state_manager(session->clp);
> >> spin_unlock(&tbl->slot_tbl_lock);
> >> @@ -4583,6 +4589,7 @@ struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp)
> >> * nfs_client struct
> >> */
> >> clp->cl_cons_state = NFS_CS_SESSION_INITING;
> >> + init_completion(&session->complete);
> >>
> >> tbl = &session->fc_slot_table;
> >> spin_lock_init(&tbl->slot_tbl_lock);
> >> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> >> index 50a1b04..f08abe8 100644
> >> --- a/fs/nfs/nfs4state.c
> >> +++ b/fs/nfs/nfs4state.c
> >> @@ -1162,8 +1162,23 @@ static void nfs4_session_recovery_handle_error(struct nfs_client *clp, int err)
> >>
> >> static int nfs4_reset_session(struct nfs_client *clp)
> >> {
> >> + struct nfs4_session *ses = clp->cl_session;
> >> + struct nfs4_slot_table *tbl = &ses->fc_slot_table;
> >> int status;
> >>
> >> + spin_lock(&tbl->slot_tbl_lock);
> >> + if (tbl->highest_used_slotid != -1) {
> >> + set_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
> >> + spin_unlock(&tbl->slot_tbl_lock);
> >> + status = wait_for_completion_interruptible(&ses->complete);
> >> + clear_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
> >> + if (status) /* -ERESTARTSYS */
> >> + goto out;
> >> + INIT_COMPLETION(ses->complete);
> >
> >
> > Looking at my own code - I need to move the INIT_COMPLETION after the
> > wait_for_completion_interruptible and before the status check so that
> > it gets called even on -ERESTARTSYS.
>
> Might there be a race with nfs41_sequence_free_slot?
> Can't you just call INIT_COMPLETION under the slot_tbl_lock
> before calling wait_for_completion_interruptible?
>
> I.e, in nfs41_sequence_free_slot:
> }
> nfs4_free_slot(tbl, res->sr_slotid);
> res->sr_slotid = NFS4_MAX_SLOT_TABLE;
> +
> + /* Signal state manager thread if session is drained */
> + if (test_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state)) {
> + spin_lock(&tbl->slot_tbl_lock);
> + if (tbl->highest_used_slotid == -1 &&
> + test_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state)) {
> + dprintk("%s COMPLETE: Session Drained\n", __func__);
> + complete(&clp->cl_session->complete);
> + }
> + spin_unlock(&tbl->slot_tbl_lock);
> + }
> }
>
> and here:
>
> static int nfs4_reset_session(struct nfs_client *clp)
> {
> + struct nfs4_session *ses = clp->cl_session;
> + struct nfs4_slot_table *tbl = &ses->fc_slot_table;
> int status;
>
> + spin_lock(&tbl->slot_tbl_lock);
> + if (tbl->highest_used_slotid != -1) {
> + set_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
> + INIT_COMPLETION(ses->complete);
> + spin_unlock(&tbl->slot_tbl_lock);
> + status = wait_for_completion_interruptible(&ses->complete);
> + clear_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
> + if (status) /* -ERESTARTSYS */
> + goto out;
>
> Benny

You shouldn't need to call it under the spinlock. Just remember to call
INIT_COMPLETION before you set NFS4CLNT_SESSION_DRAINING.

IOW:

INIT_COMPLETION(ses->complete);
spin_lock(&tbl->slot_tbl_lock);
if (tbl->highest_used_slotid != -1) {
set_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
....

Trond

--
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com