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

Benny Halevy
2009-11-12T13:29:54Z

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

>
> I'll wait for other comments before sending a fix.
>
> -->Andy
>
>
>> + } 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
>>
>> --
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