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Date:   Wed, 27 Apr 2022 17:56:14 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Dai Ngo <dai.ngo@oracle.com>
Cc:     chuck.lever@oracle.com, jlayton@redhat.com,
        viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH RFC v22 1/7] NFSD: add courteous server support for
 thread with only delegation
Message-ID: <20220427215614.GH13471@fieldses.org>
References: <1651049573-29552-1-git-send-email-dai.ngo@oracle.com>
 <1651049573-29552-2-git-send-email-dai.ngo@oracle.com>
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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.

I think what you want to do is set COURTESY first--right after you check
state_expired()--instead of doing it at the end.

--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