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

andros
2009-11-11T19:27:08Z

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