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

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

[andros]

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);
+	} else {
+		spin_unlock(&tbl->slot_tbl_lock);
+	}
+
 	status = nfs4_proc_destroy_session(clp->cl_session);
 	if (status && status != -NFS4ERR_BADSESSION &&
 	    status != -NFS4ERR_DEADSESSION) {
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 320569e..34fc6be 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -209,6 +209,7 @@ struct nfs4_session {
 	unsigned long			session_state;
 	u32				hash_alg;
 	u32				ssv_len;
+	struct completion		complete;
 
 	/* The fore and back channel */
 	struct nfs4_channel_attrs	fc_attrs;
-- 
1.6.0.6

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

[William A. (Andy) Adamson]

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 thre=
ad can
> sleep on the slot_tbl_waitq causing a deadlock.
>
> Add a completion framework to the session. =A0Have the state manager =
thread set
> a new session state (NFS4CLNT_SESSION_DRAINING) and wait for the sess=
ion 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>
> ---
> =A0fs/nfs/nfs4_fs.h =A0 =A0 =A0 =A0 =A0| =A0 =A01 +
> =A0fs/nfs/nfs4proc.c =A0 =A0 =A0 =A0 | =A0 25 ++++++++++++++++-------=
--
> =A0fs/nfs/nfs4state.c =A0 =A0 =A0 =A0| =A0 15 +++++++++++++++
> =A0include/linux/nfs_fs_sb.h | =A0 =A01 +
> =A04 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 {
> =A0 =A0 =A0 =A0NFS4CLNT_RECLAIM_NOGRACE,
> =A0 =A0 =A0 =A0NFS4CLNT_DELEGRETURN,
> =A0 =A0 =A0 =A0NFS4CLNT_SESSION_SETUP,
> + =A0 =A0 =A0 NFS4CLNT_SESSION_DRAINING,
> =A0};
>
> =A0/*
> 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_c=
lient *clp,
> =A0 =A0 =A0 =A0}
> =A0 =A0 =A0 =A0nfs4_free_slot(tbl, res->sr_slotid);
> =A0 =A0 =A0 =A0res->sr_slotid =3D NFS4_MAX_SLOT_TABLE;
> +
> + =A0 =A0 =A0 /* Signal state manager thread if session is drained */
> + =A0 =A0 =A0 if (test_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state)=
) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 spin_lock(&tbl->slot_tbl_lock);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (tbl->highest_used_slotid =3D=3D -1)=
 {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dprintk("%s COMPLETE: S=
ession Drained\n", __func__);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 complete(&clp->cl_sessi=
on->complete);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 spin_unlock(&tbl->slot_tbl_lock);
> + =A0 =A0 =A0 }
> =A0}
>
> =A0static void nfs41_sequence_done(struct nfs_client *clp,
> @@ -448,15 +458,11 @@ static int nfs41_setup_sequence(struct nfs4_ses=
sion *session,
>
> =A0 =A0 =A0 =A0spin_lock(&tbl->slot_tbl_lock);
> =A0 =A0 =A0 =A0if (test_bit(NFS4CLNT_SESSION_SETUP, &session->clp->cl=
_state)) {
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (tbl->highest_used_slotid !=3D -1) {
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 rpc_sleep_on(&tbl->slot=
_tbl_waitq, task, NULL);
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 spin_unlock(&tbl->slot_=
tbl_lock);
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 dprintk("<-- %s: Sessio=
n reset: draining\n", __func__);
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return -EAGAIN;
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> -
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* The slot table is empty; start the r=
eset thread */
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 dprintk("%s Session Reset\n", __func__)=
;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 /*
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* The state manager will wait until =
the slot table is empty.
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* Schedule the reset thread
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0*/
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 dprintk("%s Schedule Session Reset\n", =
__func__);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0rpc_sleep_on(&tbl->slot_tbl_waitq, tas=
k, NULL);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0nfs4_schedule_state_manager(session->c=
lp);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0spin_unlock(&tbl->slot_tbl_lock);
> @@ -4583,6 +4589,7 @@ struct nfs4_session *nfs4_alloc_session(struct =
nfs_client *clp)
> =A0 =A0 =A0 =A0 * nfs_client struct
> =A0 =A0 =A0 =A0 */
> =A0 =A0 =A0 =A0clp->cl_cons_state =3D NFS_CS_SESSION_INITING;
> + =A0 =A0 =A0 init_completion(&session->complete);
>
> =A0 =A0 =A0 =A0tbl =3D &session->fc_slot_table;
> =A0 =A0 =A0 =A0spin_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)
>
> =A0static int nfs4_reset_session(struct nfs_client *clp)
> =A0{
> + =A0 =A0 =A0 struct nfs4_session *ses =3D clp->cl_session;
> + =A0 =A0 =A0 struct nfs4_slot_table *tbl =3D &ses->fc_slot_table;
> =A0 =A0 =A0 =A0int status;
>
> + =A0 =A0 =A0 spin_lock(&tbl->slot_tbl_lock);
> + =A0 =A0 =A0 if (tbl->highest_used_slotid !=3D -1) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 set_bit(NFS4CLNT_SESSION_DRAINING, &clp=
->cl_state);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 spin_unlock(&tbl->slot_tbl_lock);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 status =3D wait_for_completion_interrup=
tible(&ses->complete);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 clear_bit(NFS4CLNT_SESSION_DRAINING, &c=
lp->cl_state);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (status) /* -ERESTARTSYS */
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 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.

I'll wait for other comments before sending a fix.

-->Andy


> + =A0 =A0 =A0 } else {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 spin_unlock(&tbl->slot_tbl_lock);
> + =A0 =A0 =A0 }
> +
> =A0 =A0 =A0 =A0status =3D nfs4_proc_destroy_session(clp->cl_session);
> =A0 =A0 =A0 =A0if (status && status !=3D -NFS4ERR_BADSESSION &&
> =A0 =A0 =A0 =A0 =A0 =A0status !=3D -NFS4ERR_DEADSESSION) {
> diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
> index 320569e..34fc6be 100644
> --- a/include/linux/nfs_fs_sb.h
> +++ b/include/linux/nfs_fs_sb.h
> @@ -209,6 +209,7 @@ struct nfs4_session {
> =A0 =A0 =A0 =A0unsigned long =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 sess=
ion_state;
> =A0 =A0 =A0 =A0u32 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 hash_alg;
> =A0 =A0 =A0 =A0u32 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 ssv_len;
> + =A0 =A0 =A0 struct completion =A0 =A0 =A0 =A0 =A0 =A0 =A0 complete;
>
> =A0 =A0 =A0 =A0/* The fore and back channel */
> =A0 =A0 =A0 =A0struct nfs4_channel_attrs =A0 =A0 =A0 fc_attrs;
> --
> 1.6.0.6
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" =
in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at =A0http://vger.kernel.org/majordomo-info.html
>

[PATCH 0/2] nfs41 Fix session reset deadlocks Version 2

[andros]

Fix session reset deadlocks Version 2.

These patches apply to tronds nfs-2.6 bugfix
branch (2.6.32-rc6 on top of these two already posted patches:
nfs41-fix-multiple-free-slot-calls.patch
nfs41-fix-race-on-session-reset.patch

Fix two problems reported by Trond:

0001-nfs41-remove-nfs4_recover_session.patch

Responded to comments and moved INIT_COMPLETION() call.
0002-nfs41-fix-state-manager-deadlock-in-session-reset.patch

Testing:

CONFIG_NFS_V4_1
v41 mount: Connectathon tests passed. PyNFS testclient.py SESSIONRESET tests
and the new INJECT_ERROR_CTHON test where NFS4ERR_BADSESSION was returned
every 50th SEQUENCE operation durring a Connectathon basic test run. This passed
with the session being reset 390 times from a variety of client compounds
(READ/WRITE/COMMIT/OPEN/CLOSE/ to name a few).

v4 mount: Connectathon tests passed.

no CONFIG_NFS_V4_1
v4 mount: Connectathon tests passed.

-->Andy

[PATCH 1/2] nfs41: remove nfs4_recover_session

[andros]

From: Andy Adamson <andros@netapp.com>

nfs4_recover_session can put rpciod to sleep. Just use nfs4_schedule_recovery.

Reported-by: Trond Myklebust <trond.myklebust@netapp.com>
Signed-off-by: Andy Adamson <andros@netapp.com>
---
 fs/nfs/nfs4proc.c |   26 +++-----------------------
 1 files changed, 3 insertions(+), 23 deletions(-)

diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index 0f1afde..44d1c14 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -427,24 +427,6 @@ out:
 	return ret_id;
 }
 
-static int nfs4_recover_session(struct nfs4_session *session)
-{
-	struct nfs_client *clp = session->clp;
-	unsigned int loop;
-	int ret;
-
-	for (loop = NFS4_MAX_LOOP_ON_RECOVER; loop != 0; loop--) {
-		ret = nfs4_wait_clnt_recover(clp);
-		if (ret != 0)
-			break;
-		if (!test_bit(NFS4CLNT_SESSION_SETUP, &clp->cl_state))
-			break;
-		nfs4_schedule_state_manager(clp);
-		ret = -EIO;
-	}
-	return ret;
-}
-
 static int nfs41_setup_sequence(struct nfs4_session *session,
 				struct nfs4_sequence_args *args,
 				struct nfs4_sequence_res *res,
@@ -453,7 +435,6 @@ static int nfs41_setup_sequence(struct nfs4_session *session,
 {
 	struct nfs4_slot *slot;
 	struct nfs4_slot_table *tbl;
-	int status = 0;
 	u8 slotid;
 
 	dprintk("--> %s\n", __func__);
@@ -476,11 +457,10 @@ static int nfs41_setup_sequence(struct nfs4_session *session,
 
 		/* The slot table is empty; start the reset thread */
 		dprintk("%s 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);
-		status = nfs4_recover_session(session);
-		if (status)
-			return status;
-		spin_lock(&tbl->slot_tbl_lock);
+		return -EAGAIN;
 	}
 
 	slotid = nfs4_find_slot(tbl, task);
-- 
1.6.0.6

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

[andros]

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..2e93b61 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;
 
+	INIT_COMPLETION(ses->complete);
+	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;
+	} else {
+		spin_unlock(&tbl->slot_tbl_lock);
+	}
+
 	status = nfs4_proc_destroy_session(clp->cl_session);
 	if (status && status != -NFS4ERR_BADSESSION &&
 	    status != -NFS4ERR_DEADSESSION) {
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 320569e..34fc6be 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -209,6 +209,7 @@ struct nfs4_session {
 	unsigned long			session_state;
 	u32				hash_alg;
 	u32				ssv_len;
+	struct completion		complete;
 
 	/* The fore and back channel */
 	struct nfs4_channel_attrs	fc_attrs;
-- 
1.6.0.6