Re: [PATCH RFC v22 1/7] NFSD: add courteous server support for thread with only delegation

[dai.ngo@oracle.com]

On 4/27/22 6:52 PM, J. Bruce Fields wrote:
> On Wed, Apr 27, 2022 at 03:52:37PM -0700, dai.ngo@oracle.com wrote:
>> On 4/27/22 2:56 PM, J. Bruce Fields wrote:
>>> On Wed, Apr 27, 2022 at 01:52:47AM -0700, Dai Ngo wrote:
>>>> This patch provides courteous server support for delegation only.
>>>> Only expired client with delegation but no conflict and no open
>>>> or lock state is allowed to be in COURTESY state.
>>>>
>>>> Delegation conflict with COURTESY/EXPIRABLE client is resolved by
>>>> setting it to EXPIRABLE, queue work for the laundromat and return
>>>> delay to the caller. Conflict is resolved when the laudromat runs
>>>> and expires the EXIRABLE client while the NFS client retries the
>>>> OPEN request. Local thread request that gets conflict is doing the
>>>> retry in _break_lease.
>>>>
>>>> Client in COURTESY or EXPIRABLE state is allowed to reconnect and
>>>> continues to have access to its state. Access to the nfs4_client by
>>>> the reconnecting thread and the laundromat is serialized via the
>>>> client_lock.
>>>>
>>>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>>>> ---
>>>>   fs/nfsd/nfs4state.c | 86 +++++++++++++++++++++++++++++++++++++++++++++--------
>>>>   fs/nfsd/nfsd.h      |  1 +
>>>>   fs/nfsd/state.h     | 32 ++++++++++++++++++++
>>>>   3 files changed, 106 insertions(+), 13 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>>>> index 234e852fcdfa..216bd77a8764 100644
>>>> --- a/fs/nfsd/nfs4state.c
>>>> +++ b/fs/nfsd/nfs4state.c
>>>> @@ -125,6 +125,8 @@ static void free_session(struct nfsd4_session *);
>>>>   static const struct nfsd4_callback_ops nfsd4_cb_recall_ops;
>>>>   static const struct nfsd4_callback_ops nfsd4_cb_notify_lock_ops;
>>>> +static struct workqueue_struct *laundry_wq;
>>>> +
>>>>   static bool is_session_dead(struct nfsd4_session *ses)
>>>>   {
>>>>   	return ses->se_flags & NFS4_SESSION_DEAD;
>>>> @@ -152,6 +154,7 @@ static __be32 get_client_locked(struct nfs4_client *clp)
>>>>   	if (is_client_expired(clp))
>>>>   		return nfserr_expired;
>>>>   	atomic_inc(&clp->cl_rpc_users);
>>>> +	clp->cl_state = NFSD4_ACTIVE;
>>>>   	return nfs_ok;
>>>>   }
>>>> @@ -172,6 +175,7 @@ renew_client_locked(struct nfs4_client *clp)
>>>>   	list_move_tail(&clp->cl_lru, &nn->client_lru);
>>>>   	clp->cl_time = ktime_get_boottime_seconds();
>>>> +	clp->cl_state = NFSD4_ACTIVE;
>>>>   }
>>>>   static void put_client_renew_locked(struct nfs4_client *clp)
>>>> @@ -2004,6 +2008,7 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
>>>>   	idr_init(&clp->cl_stateids);
>>>>   	atomic_set(&clp->cl_rpc_users, 0);
>>>>   	clp->cl_cb_state = NFSD4_CB_UNKNOWN;
>>>> +	clp->cl_state = NFSD4_ACTIVE;
>>>>   	INIT_LIST_HEAD(&clp->cl_idhash);
>>>>   	INIT_LIST_HEAD(&clp->cl_openowners);
>>>>   	INIT_LIST_HEAD(&clp->cl_delegations);
>>>> @@ -4694,9 +4699,16 @@ nfsd_break_deleg_cb(struct file_lock *fl)
>>>>   	bool ret = false;
>>>>   	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
>>>>   	struct nfs4_file *fp = dp->dl_stid.sc_file;
>>>> +	struct nfs4_client *clp = dp->dl_stid.sc_client;
>>>> +	struct nfsd_net *nn;
>>>>   	trace_nfsd_cb_recall(&dp->dl_stid);
>>>> +	if (!try_to_expire_client(clp)) {
>>>> +		nn = net_generic(clp->net, nfsd_net_id);
>>>> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
>>>> +	}
>>>> +
>>>>   	/*
>>>>   	 * We don't want the locks code to timeout the lease for us;
>>>>   	 * we'll remove it ourself if a delegation isn't returned
>>>> @@ -5605,6 +5617,65 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
>>>>   }
>>>>   #endif
>>>> +/*
>>>> + * place holder for now, no check for lock blockers yet
>>>> + */
>>>> +static bool
>>>> +nfs4_anylock_blockers(struct nfs4_client *clp)
>>>> +{
>>>> +	/*
>>>> +	 * don't want to check for delegation conflict here since
>>>> +	 * we need the state_lock for it. The laundromat willexpire
>>>> +	 * COURTESY later when checking for delegation recall timeout.
>>>> +	 */
>>>> +	return false;
>>>> +}
>>>> +
>>>> +static bool client_has_state_tmp(struct nfs4_client *clp)
>>>> +{
>>>> +	if (!list_empty(&clp->cl_delegations) &&
>>>> +			!client_has_openowners(clp) &&
>>>> +			list_empty(&clp->async_copies))
>>>> +		return true;
>>>> +	return false;
>>>> +}
>>>> +
>>>> +static void
>>>> +nfs4_get_client_reaplist(struct nfsd_net *nn, struct list_head *reaplist,
>>>> +				struct laundry_time *lt)
>>>> +{
>>>> +	struct list_head *pos, *next;
>>>> +	struct nfs4_client *clp;
>>>> +	bool cour;
>>>> +
>>>> +	INIT_LIST_HEAD(reaplist);
>>>> +	spin_lock(&nn->client_lock);
>>>> +	list_for_each_safe(pos, next, &nn->client_lru) {
>>>> +		clp = list_entry(pos, struct nfs4_client, cl_lru);
>>>> +		if (clp->cl_state == NFSD4_EXPIRABLE)
>>>> +			goto exp_client;
>>>> +		if (!state_expired(lt, clp->cl_time))
>>>> +			break;
>>>> +		if (!client_has_state_tmp(clp))
>>>> +			goto exp_client;
>>>> +		cour = (clp->cl_state == NFSD4_COURTESY);
>>>> +		if (cour && ktime_get_boottime_seconds() >=
>>>> +				(clp->cl_time + NFSD_COURTESY_CLIENT_TIMEOUT)) {
>>>> +			goto exp_client;
>>>> +		}
>>>> +		if (nfs4_anylock_blockers(clp)) {
>>>> +exp_client:
>>>> +			if (mark_client_expired_locked(clp))
>>>> +				continue;
>>>> +			list_add(&clp->cl_lru, reaplist);
>>>> +			continue;
>>>> +		}
>>>> +		if (!cour)
>>>> +			cmpxchg(&clp->cl_state, NFSD4_ACTIVE, NFSD4_COURTESY);
>>> I just noticed there's a small race here: a lock conflict (for example)
>>> could intervene between checking nfs4_anylock_blockers and setting
>>> COURTESY.
>> If there is lock conflict intervenes before setting COURTESY then that
>> lock request is denied since the client is ACTIVE. Does NFSv4, NLM
>> client retry the lock request? if it does then on next retry the
>> COURTESY client will be expired.
> I'm thinking of a local request for a blocking lock.  Yes, the request
> will be denied, but then the process will block on the lock forever
> (well, for 24 hours anyway).

got it.

>
>>> I think what you want to do is set COURTESY first--right after you check
>>> state_expired()--instead of doing it at the end.
>> Yes, I can make this change. I think this still has a tiny window
>> where a lock conflict comes in after state_expired and before
>> COURTESY is set?
> No, I think it's OK.  A lock that comes before COURTESY is set will be
> caught by nfs4_anylock_blockers().

That's right.

-Dai

>
> --b.
>
>> -Dai
>>
>>> --b.
>>>
>>>> +	}
>>>> +	spin_unlock(&nn->client_lock);
>>>> +}
>>>> +
>>>>   static time64_t
>>>>   nfs4_laundromat(struct nfsd_net *nn)
>>>>   {
>>>> @@ -5627,7 +5698,6 @@ nfs4_laundromat(struct nfsd_net *nn)
>>>>   		goto out;
>>>>   	}
>>>>   	nfsd4_end_grace(nn);
>>>> -	INIT_LIST_HEAD(&reaplist);
>>>>   	spin_lock(&nn->s2s_cp_lock);
>>>>   	idr_for_each_entry(&nn->s2s_cp_stateids, cps_t, i) {
>>>> @@ -5637,17 +5707,7 @@ nfs4_laundromat(struct nfsd_net *nn)
>>>>   			_free_cpntf_state_locked(nn, cps);
>>>>   	}
>>>>   	spin_unlock(&nn->s2s_cp_lock);
>>>> -
>>>> -	spin_lock(&nn->client_lock);
>>>> -	list_for_each_safe(pos, next, &nn->client_lru) {
>>>> -		clp = list_entry(pos, struct nfs4_client, cl_lru);
>>>> -		if (!state_expired(&lt, clp->cl_time))
>>>> -			break;
>>>> -		if (mark_client_expired_locked(clp))
>>>> -			continue;
>>>> -		list_add(&clp->cl_lru, &reaplist);
>>>> -	}
>>>> -	spin_unlock(&nn->client_lock);
>>>> +	nfs4_get_client_reaplist(nn, &reaplist, &lt);
>>>>   	list_for_each_safe(pos, next, &reaplist) {
>>>>   		clp = list_entry(pos, struct nfs4_client, cl_lru);
>>>>   		trace_nfsd_clid_purged(&clp->cl_clientid);
>>>> @@ -5657,6 +5717,7 @@ nfs4_laundromat(struct nfsd_net *nn)
>>>>   	spin_lock(&state_lock);
>>>>   	list_for_each_safe(pos, next, &nn->del_recall_lru) {
>>>>   		dp = list_entry (pos, struct nfs4_delegation, dl_recall_lru);
>>>> +		try_to_expire_client(dp->dl_stid.sc_client);
>>>>   		if (!state_expired(&lt, dp->dl_time))
>>>>   			break;
>>>>   		WARN_ON(!unhash_delegation_locked(dp));
>>>> @@ -5722,7 +5783,6 @@ nfs4_laundromat(struct nfsd_net *nn)
>>>>   	return max_t(time64_t, lt.new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
>>>>   }
>>>> -static struct workqueue_struct *laundry_wq;
>>>>   static void laundromat_main(struct work_struct *);
>>>>   static void
>>>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>>>> index 4fc1fd639527..23996c6ca75e 100644
>>>> --- a/fs/nfsd/nfsd.h
>>>> +++ b/fs/nfsd/nfsd.h
>>>> @@ -336,6 +336,7 @@ void		nfsd_lockd_shutdown(void);
>>>>   #define COMPOUND_ERR_SLACK_SPACE	16     /* OP_SETATTR */
>>>>   #define NFSD_LAUNDROMAT_MINTIMEOUT      1   /* seconds */
>>>> +#define	NFSD_COURTESY_CLIENT_TIMEOUT	(24 * 60 * 60)	/* seconds */
>>>>   /*
>>>>    * The following attributes are currently not supported by the NFSv4 server:
>>>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>>>> index 95457cfd37fc..6130376c438b 100644
>>>> --- a/fs/nfsd/state.h
>>>> +++ b/fs/nfsd/state.h
>>>> @@ -283,6 +283,28 @@ struct nfsd4_sessionid {
>>>>   #define HEXDIR_LEN     33 /* hex version of 16 byte md5 of cl_name plus '\0' */
>>>>   /*
>>>> + *       State                Meaning                  Where set
>>>> + * --------------------------------------------------------------------------
>>>> + * | NFSD4_ACTIVE      | Confirmed, active    | Default                     |
>>>> + * |------------------- ----------------------------------------------------|
>>>> + * | NFSD4_COURTESY    | Courtesy state.      | nfs4_get_client_reaplist    |
>>>> + * |                   | Lease/lock/share     |                             |
>>>> + * |                   | reservation conflict |                             |
>>>> + * |                   | can cause Courtesy   |                             |
>>>> + * |                   | client to be expired |                             |
>>>> + * |------------------------------------------------------------------------|
>>>> + * | NFSD4_EXPIRABLE   | Courtesy client to be| nfs4_laundromat             |
>>>> + * |                   | expired by Laundromat| try_to_expire_client        |
>>>> + * |                   | due to conflict      |                             |
>>>> + * |------------------------------------------------------------------------|
>>>> + */
>>>> +enum {
>>>> +	NFSD4_ACTIVE = 0,
>>>> +	NFSD4_COURTESY,
>>>> +	NFSD4_EXPIRABLE,
>>>> +};
>>>> +
>>>> +/*
>>>>    * struct nfs4_client - one per client.  Clientids live here.
>>>>    *
>>>>    * The initial object created by an NFS client using SETCLIENTID (for NFSv4.0)
>>>> @@ -385,6 +407,8 @@ struct nfs4_client {
>>>>   	struct list_head	async_copies;	/* list of async copies */
>>>>   	spinlock_t		async_lock;	/* lock for async copies */
>>>>   	atomic_t		cl_cb_inflight;	/* Outstanding callbacks */
>>>> +
>>>> +	unsigned int		cl_state;
>>>>   };
>>>>   /* struct nfs4_client_reset
>>>> @@ -702,4 +726,12 @@ extern void nfsd4_client_record_remove(struct nfs4_client *clp);
>>>>   extern int nfsd4_client_record_check(struct nfs4_client *clp);
>>>>   extern void nfsd4_record_grace_done(struct nfsd_net *nn);
>>>> +static inline bool try_to_expire_client(struct nfs4_client *clp)
>>>> +{
>>>> +	bool ret;
>>>> +
>>>> +	ret = NFSD4_ACTIVE ==
>>>> +		cmpxchg(&clp->cl_state, NFSD4_COURTESY, NFSD4_EXPIRABLE);
>>>> +	return ret;
>>>> +}
>>>>   #endif   /* NFSD4_STATE_H */
>>>> -- 
>>>> 2.9.5