[RFC,v9,2/2] nfsd: Initial implementation of NFSv4 Courteous Server

Commit Message

Dai Ngo Jan. 10, 2022, 6:50 p.m. UTC

Currently an NFSv4 client must maintain its lease by using the at least
one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
a singleton SEQUENCE (4.1) at least once during each lease period. If the
client fails to renew the lease, for any reason, the Linux server expunges
the state tokens immediately upon detection of the "failure to renew the
lease" condition and begins returning NFS4ERR_EXPIRED if the client should
reconnect and attempt to use the (now) expired state.

The default lease period for the Linux server is 90 seconds.  The typical
client cuts that in half and will issue a lease renewing operation every
45 seconds. The 90 second lease period is very short considering the
potential for moderately long term network partitions.  A network partition
refers to any loss of network connectivity between the NFS client and the
NFS server, regardless of its root cause.  This includes NIC failures, NIC
driver bugs, network misconfigurations & administrative errors, routers &
switches crashing and/or having software updates applied, even down to
cables being physically pulled.  In most cases, these network failures are
transient, although the duration is unknown.

A server which does not immediately expunge the state on lease expiration
is known as a Courteous Server.  A Courteous Server continues to recognize
previously generated state tokens as valid until conflict arises between
the expired state and the requests from another client, or the server
reboots.

The initial implementation of the Courteous Server will do the following:

. when the laundromat thread detects an expired client and if that client
still has established states on the Linux server and there is no waiters
for the client's locks then mark the client as a COURTESY_CLIENT and skip
destroying the client and all its states, otherwise destroy the client as
usual.

. detects conflict of OPEN request with COURTESY_CLIENT, destroys the
expired client and all its states, skips the delegation recall then allows
the conflicting request to succeed.

. detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
requests with COURTESY_CLIENT, destroys the expired client and all its
states then allows the conflicting request to succeed.

. detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
requests with COURTESY_CLIENT, destroys the expired client and all its
states then allows the conflicting request to succeed.

Signed-off-by: Dai Ngo <[e-mail]>
---
 fs/nfsd/nfs4state.c | 323 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 fs/nfsd/state.h     |   8 ++
 2 files changed, 323 insertions(+), 8 deletions(-)

Comments

Chuck Lever Jan. 10, 2022, 11:17 p.m. UTC | #1

Hi Dai-

Still getting the feel of the new approach, but I have
made some comments inline...


> On Jan 10, 2022, at 1:50 PM, Dai Ngo <[e-mail]> wrote:
> 
> Currently an NFSv4 client must maintain its lease by using the at least
> one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
> a singleton SEQUENCE (4.1) at least once during each lease period. If the
> client fails to renew the lease, for any reason, the Linux server expunges
> the state tokens immediately upon detection of the "failure to renew the
> lease" condition and begins returning NFS4ERR_EXPIRED if the client should
> reconnect and attempt to use the (now) expired state.
> 
> The default lease period for the Linux server is 90 seconds.  The typical
> client cuts that in half and will issue a lease renewing operation every
> 45 seconds. The 90 second lease period is very short considering the
> potential for moderately long term network partitions.  A network partition
> refers to any loss of network connectivity between the NFS client and the
> NFS server, regardless of its root cause.  This includes NIC failures, NIC
> driver bugs, network misconfigurations & administrative errors, routers &
> switches crashing and/or having software updates applied, even down to
> cables being physically pulled.  In most cases, these network failures are
> transient, although the duration is unknown.
> 
> A server which does not immediately expunge the state on lease expiration
> is known as a Courteous Server.  A Courteous Server continues to recognize
> previously generated state tokens as valid until conflict arises between
> the expired state and the requests from another client, or the server
> reboots.
> 
> The initial implementation of the Courteous Server will do the following:
> 
> . when the laundromat thread detects an expired client and if that client
> still has established states on the Linux server and there is no waiters
> for the client's locks then mark the client as a COURTESY_CLIENT and skip
> destroying the client and all its states, otherwise destroy the client as
> usual.
> 
> . detects conflict of OPEN request with COURTESY_CLIENT, destroys the
> expired client and all its states, skips the delegation recall then allows
> the conflicting request to succeed.
> 
> . detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
> requests with COURTESY_CLIENT, destroys the expired client and all its
> states then allows the conflicting request to succeed.
> 
> . detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
> requests with COURTESY_CLIENT, destroys the expired client and all its
> states then allows the conflicting request to succeed.
> 
> Signed-off-by: Dai Ngo <[e-mail]>
> ---
> fs/nfsd/nfs4state.c | 323 ++++++++++++++++++++++++++++++++++++++++++++++++++--
> fs/nfsd/state.h     |   8 ++
> 2 files changed, 323 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 3f4027a5de88..e7fa4da44835 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -125,6 +125,11 @@ 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 void laundromat_main(struct work_struct *);
> +
> +static const int courtesy_client_expiry = (24 * 60 * 60);	/* in secs */
> +
> static bool is_session_dead(struct nfsd4_session *ses)
> {
> 	return ses->se_flags & NFS4_SESSION_DEAD;
> @@ -155,8 +160,10 @@ static __be32 get_client_locked(struct nfs4_client *clp)
> 	return nfs_ok;
> }
> 
> -/* must be called under the client_lock */
> +/* must be called under the client_lock
> static inline void
> +*/
> +void
> renew_client_locked(struct nfs4_client *clp)
> {
> 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> @@ -172,7 +179,9 @@ renew_client_locked(struct nfs4_client *clp)
> 
> 	list_move_tail(&clp->cl_lru, &nn->client_lru);
> 	clp->cl_time = ktime_get_boottime_seconds();
> +	clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> }
> +EXPORT_SYMBOL_GPL(renew_client_locked);

I don't see renew_client_locked() being called from outside
fs/nfsd/nfs4state.c, and the patch doesn't add a global
declaration.

Please leave this function as "static inline void".


> static void put_client_renew_locked(struct nfs4_client *clp)
> {
> @@ -1912,10 +1921,22 @@ find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid, struct net *net,
> {
> 	struct nfsd4_session *session;
> 	__be32 status = nfserr_badsession;
> +	struct nfs4_client *clp;
> 
> 	session = __find_in_sessionid_hashtbl(sessionid, net);
> 	if (!session)
> 		goto out;
> +	clp = session->se_client;
> +	if (clp) {
> +		spin_lock(&clp->cl_cs_lock);
> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags)) {
> +			spin_unlock(&clp->cl_cs_lock);
> +			session = NULL;
> +			goto out;
> +		}
> +		clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> +		spin_unlock(&clp->cl_cs_lock);
> +	}
> 	status = nfsd4_get_session_locked(session);
> 	if (status)
> 		session = NULL;
> @@ -1992,6 +2013,7 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
> 	INIT_LIST_HEAD(&clp->async_copies);
> 	spin_lock_init(&clp->async_lock);
> 	spin_lock_init(&clp->cl_lock);
> +	spin_lock_init(&clp->cl_cs_lock);
> 	rpc_init_wait_queue(&clp->cl_cb_waitq, "Backchannel slot table");
> 	return clp;
> err_no_hashtbl:
> @@ -2389,6 +2411,10 @@ static int client_info_show(struct seq_file *m, void *v)
> 		seq_puts(m, "status: confirmed\n");
> 	else
> 		seq_puts(m, "status: unconfirmed\n");
> +	seq_printf(m, "courtesy client: %s\n",
> +		test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ? "yes" : "no");
> +	seq_printf(m, "seconds from last renew: %lld\n",
> +		ktime_get_boottime_seconds() - clp->cl_time);
> 	seq_printf(m, "name: ");
> 	seq_quote_mem(m, clp->cl_name.data, clp->cl_name.len);
> 	seq_printf(m, "\nminor version: %d\n", clp->cl_minorversion);
> @@ -2809,8 +2835,17 @@ find_clp_in_name_tree(struct xdr_netobj *name, struct rb_root *root)
> 			node = node->rb_left;
> 		else if (cmp < 0)
> 			node = node->rb_right;
> -		else
> -			return clp;
> +		else {
> +			spin_lock(&clp->cl_cs_lock);
> +			if (!test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
> +					&clp->cl_flags)) {
> +				clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> +				spin_unlock(&clp->cl_cs_lock);
> +				return clp;
> +			}
> +			spin_unlock(&clp->cl_cs_lock);
> +			return NULL;
> +		}
> 	}
> 	return NULL;
> }
> @@ -2856,6 +2891,14 @@ find_client_in_id_table(struct list_head *tbl, clientid_t *clid, bool sessions)
> 		if (same_clid(&clp->cl_clientid, clid)) {
> 			if ((bool)clp->cl_minorversion != sessions)
> 				return NULL;
> +			spin_lock(&clp->cl_cs_lock);
> +			if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
> +					&clp->cl_flags)) {
> +				spin_unlock(&clp->cl_cs_lock);
> +				continue;
> +			}
> +			clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> +			spin_unlock(&clp->cl_cs_lock);

I'm wondering about the transition from COURTESY to active.
Does that need to be synchronous with the client tracking
database?


> 			renew_client_locked(clp);
> 			return clp;
> 		}
> @@ -4662,6 +4705,36 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
> 	nfsd4_run_cb(&dp->dl_recall);
> }
> 
> +/*
> + * This function is called when a file is opened and there is a
> + * delegation conflict with another client. If the other client
> + * is a courtesy client then kick start the laundromat to destroy
> + * it.
> + */
> +static bool
> +nfsd_check_courtesy_client(struct nfs4_delegation *dp)
> +{
> +	struct svc_rqst *rqst;
> +	struct nfs4_client *clp = dp->dl_recall.cb_clp;
> +	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> +
> +	if (!i_am_nfsd())
> +		goto out;
> +	rqst = kthread_data(current);
> +	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
> +		return false;
> +out:
> +	spin_lock(&clp->cl_cs_lock);
> +	if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
> +		set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
> +		spin_unlock(&clp->cl_cs_lock);
> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);

I'm not sure what is the purpose of the mod_delayed_work()
here and below. What's the harm in leaving a DESTROYED
nfs4_client around until the laundromat runs again? Won't
it run every "grace period" seconds anyway?

I didn't think we were depending on the laundromat to
resolve edge case races, so if a call to a scheduler
function isn't totally necessary in this code, I prefer
that it be left out.


> +		return true;
> +	}
> +	spin_unlock(&clp->cl_cs_lock);
> +	return false;
> +}
> +
> /* Called from break_lease() with i_lock held. */
> static bool
> nfsd_break_deleg_cb(struct file_lock *fl)
> @@ -4670,6 +4743,8 @@ nfsd_break_deleg_cb(struct file_lock *fl)
> 	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
> 	struct nfs4_file *fp = dp->dl_stid.sc_file;
> 
> +	if (nfsd_check_courtesy_client(dp))
> +		return false;
> 	trace_nfsd_cb_recall(&dp->dl_stid);
> 
> 	/*
> @@ -4912,7 +4987,128 @@ nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
> 	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
> }
> 
> -static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> +static bool
> +__nfs4_check_access_deny_bmap(struct nfs4_ol_stateid *stp, u32 access,
> +			bool share_access)
> +{
> +	if (share_access) {
> +		if (!stp->st_deny_bmap)
> +			return false;
> +
> +		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
> +			(access & NFS4_SHARE_ACCESS_READ &&
> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
> +			(access & NFS4_SHARE_ACCESS_WRITE &&
> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
> +			return true;
> +		}
> +		return false;
> +	}
> +	if ((access & NFS4_SHARE_DENY_BOTH) ||
> +		(access & NFS4_SHARE_DENY_READ &&
> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
> +		(access & NFS4_SHARE_DENY_WRITE &&
> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
> +		return true;
> +	}
> +	return false;
> +}
> +
> +/*
> + * Check all files belong to the specified client to determine if there is
> + * any conflict with the specified access_mode/deny_mode of the file 'fp.
> + *
> + * If share_access is true then 'access' is the access mode. Check if
> + * this access mode conflicts with current deny mode of the file.
> + *
> + * If share_access is false then 'access' the deny mode. Check if
> + * this deny mode conflicts with current access mode of the file.
> + */
> +static bool
> +nfs4_check_access_deny_bmap(struct nfs4_client *clp, struct nfs4_file *fp,
> +		struct nfs4_ol_stateid *st, u32 access, bool share_access)
> +{
> +	int i;
> +	struct nfs4_openowner *oo;
> +	struct nfs4_stateowner *so, *tmp;
> +	struct nfs4_ol_stateid *stp, *stmp;
> +
> +	spin_lock(&clp->cl_lock);
> +	for (i = 0; i < OWNER_HASH_SIZE; i++) {
> +		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
> +					so_strhash) {
> +			if (!so->so_is_open_owner)
> +				continue;
> +			oo = openowner(so);
> +			list_for_each_entry_safe(stp, stmp,
> +				&oo->oo_owner.so_stateids, st_perstateowner) {
> +				if (stp == st || stp->st_stid.sc_file != fp)
> +					continue;
> +				if (__nfs4_check_access_deny_bmap(stp, access,
> +							share_access)) {
> +					spin_unlock(&clp->cl_lock);
> +					return true;
> +				}
> +			}
> +		}
> +	}
> +	spin_unlock(&clp->cl_lock);
> +	return false;
> +}
> +
> +/*
> + * This function is called to check whether nfserr_share_denied should
> + * be returning to client.
> + *
> + * access: is op_share_access if share_access is true.
> + *	   Check if access mode, op_share_access, would conflict with
> + *	   the current deny mode of the file 'fp'.
> + * access: is op_share_deny if share_access is true.
> + *	   Check if the deny mode, op_share_deny, would conflict with
> + *	   current access of the file 'fp'.
> + * stp:    skip checking this entry.
> + *
> + * Function returns:
> + *	true  - access/deny mode conflict with courtesy client(s).
> + *		Caller to return nfserr_jukebox while client(s) being expired.
> + *	false - access/deny mode conflict with non-courtesy client.
> + *		Caller to return nfserr_share_denied to client.
> + */
> +static bool
> +nfs4_conflict_courtesy_clients(struct svc_rqst *rqstp, struct nfs4_file *fp,
> +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
> +{
> +	struct nfs4_client *cl;
> +	bool conflict = false;
> +	int async_cnt = 0;
> +	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> +
> +	spin_lock(&nn->client_lock);
> +	list_for_each_entry(cl, &nn->client_lru, cl_lru) {
> +		if (!nfs4_check_access_deny_bmap(cl, fp, stp, access, share_access))
> +			continue;
> +		spin_lock(&cl->cl_cs_lock);
> +		if (test_bit(NFSD4_COURTESY_CLIENT, &cl->cl_flags)) {
> +			set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &cl->cl_flags);
> +			async_cnt++;

You can get rid of async_cnt. Just set conflict = true
after unlocking cl_cs_lock. And again, maybe that
mod_delayed_work() call site isn't necessary.


> +			spin_unlock(&cl->cl_cs_lock);
> +			continue;
> +		}
> +		/* conflict with non-courtesy client */
> +		spin_unlock(&cl->cl_cs_lock);
> +		conflict = false;
> +		break;
> +	}
> +	spin_unlock(&nn->client_lock);
> +	if (async_cnt) {
> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> +		conflict = true;
> +	}
> +	return conflict;
> +}
> +
> +static __be32
> +nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> 		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
> 		struct nfsd4_open *open)
> {
> @@ -4931,6 +5127,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> 	status = nfs4_file_check_deny(fp, open->op_share_deny);
> 	if (status != nfs_ok) {
> 		spin_unlock(&fp->fi_lock);
> +		if (status != nfserr_share_denied)
> +			goto out;
> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
> +				stp, open->op_share_deny, false))
> +			status = nfserr_jukebox;
> 		goto out;
> 	}
> 
> @@ -4938,6 +5139,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> 	status = nfs4_file_get_access(fp, open->op_share_access);
> 	if (status != nfs_ok) {
> 		spin_unlock(&fp->fi_lock);
> +		if (status != nfserr_share_denied)
> +			goto out;
> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
> +				stp, open->op_share_access, true))
> +			status = nfserr_jukebox;
> 		goto out;
> 	}
> 
> @@ -5572,6 +5778,47 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
> }
> #endif
> 
> +static
> +bool nfs4_anylock_conflict(struct nfs4_client *clp)

This function assumes the caller holds cl_lock. That bears
mentioning here in a comment. Convention suggests adding
"_locked" to the function name too, just like
renew_client_locked() above.

Also, nit: kernel style is either:

static bool
nfs4_anylock_conflict(

or

static bool nfs4_anylock_conflict(


> +{
> +	int i;
> +	struct nfs4_stateowner *so, *tmp;
> +	struct nfs4_lockowner *lo;
> +	struct nfs4_ol_stateid *stp;
> +	struct nfs4_file *nf;
> +	struct inode *ino;
> +	struct file_lock_context *ctx;
> +	struct file_lock *fl;
> +
> +	for (i = 0; i < OWNER_HASH_SIZE; i++) {
> +		/* scan each lock owner */
> +		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
> +				so_strhash) {
> +			if (so->so_is_open_owner)
> +				continue;
> +
> +			/* scan lock states of this lock owner */
> +			lo = lockowner(so);
> +			list_for_each_entry(stp, &lo->lo_owner.so_stateids,
> +					st_perstateowner) {
> +				nf = stp->st_stid.sc_file;
> +				ino = nf->fi_inode;
> +				ctx = ino->i_flctx;
> +				if (!ctx)
> +					continue;
> +				/* check each lock belongs to this lock state */
> +				list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
> +					if (fl->fl_owner != lo)
> +						continue;
> +					if (!list_empty(&fl->fl_blocked_requests))
> +						return true;
> +				}
> +			}
> +		}
> +	}
> +	return false;
> +}
> +
> static time64_t
> nfs4_laundromat(struct nfsd_net *nn)
> {
> @@ -5587,7 +5834,9 @@ nfs4_laundromat(struct nfsd_net *nn)
> 	};
> 	struct nfs4_cpntf_state *cps;
> 	copy_stateid_t *cps_t;
> +	struct nfs4_stid *stid;
> 	int i;
> +	int id;
> 
> 	if (clients_still_reclaiming(nn)) {
> 		lt.new_timeo = 0;
> @@ -5608,8 +5857,41 @@ nfs4_laundromat(struct nfsd_net *nn)
> 	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))
> +		spin_lock(&clp->cl_cs_lock);
> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags))
> +			goto exp_client;
> +		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
> +			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
> +				goto exp_client;
> +			/*
> +			 * after umount, v4.0 client is still around
> +			 * waiting to be expired. Check again and if
> +			 * it has no state then expire it.
> +			 */
> +			if (clp->cl_minorversion) {
> +				spin_unlock(&clp->cl_cs_lock);
> +				continue;
> +			}
> +		}
> +		if (!state_expired(&lt, clp->cl_time)) {

Now that clients go from active -> COURTEOUS -> DESTROY,
why is this check still necessary? If it truly is, a brief
explanation/comment would help.


> +			spin_unlock(&clp->cl_cs_lock);
> 			break;
> +		}
> +		id = 0;
> +		spin_lock(&clp->cl_lock);
> +		stid = idr_get_next(&clp->cl_stateids, &id);
> +		if (stid && !nfs4_anylock_conflict(clp)) {
> +			/* client still has states */
> +			spin_unlock(&clp->cl_lock);
> +			clp->courtesy_client_expiry =
> +				ktime_get_boottime_seconds() + courtesy_client_expiry;
> +			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> +			spin_unlock(&clp->cl_cs_lock);
> +			continue;
> +		}
> +		spin_unlock(&clp->cl_lock);
> +exp_client:
> +		spin_unlock(&clp->cl_cs_lock);
> 		if (mark_client_expired_locked(clp))
> 			continue;
> 		list_add(&clp->cl_lru, &reaplist);
> @@ -5689,9 +5971,6 @@ 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 *);
> -

If the new mod_delayed_work() call sites aren't necessary,
then these static definitions can be left here.


> static void
> laundromat_main(struct work_struct *laundry)
> {
> @@ -6496,6 +6775,33 @@ nfs4_transform_lock_offset(struct file_lock *lock)
> 		lock->fl_end = OFFSET_MAX;
> }
> 
> +/*
> + * Return true if lock can be resolved by expiring
> + * courtesy client else return false.
> + */

Since this function is invoked from outside of nfs4state.c,
please turn the above comment into a kerneldoc comment, eg:

/**
 * nfsd4_fl_expire_lock - check if lock conflict can be resolved
 * @fl: pointer to file_lock with a potential conflict
 *
 * Return values:
 *   %true: No conflict exists
 *   %false: Lock conflict can't be resolved
 */


> +static bool
> +nfsd4_fl_expire_lock(struct file_lock *fl)
> +{
> +	struct nfs4_lockowner *lo;
> +	struct nfs4_client *clp;
> +	struct nfsd_net *nn;
> +
> +	if (!fl)
> +		return false;
> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
> +	clp = lo->lo_owner.so_client;
> +	spin_lock(&clp->cl_cs_lock);
> +	if (!test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
> +		spin_unlock(&clp->cl_cs_lock);
> +		return false;
> +	}
> +	nn = net_generic(clp->net, nfsd_net_id);

Why is "nn =" inside the cl_cs_lock critical section here?
I don't think that lock protects clp->net. Also, if the
mod_delayed_work() call isn't needed here, then @nn can
be removed too.


> +	set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
> +	spin_unlock(&clp->cl_cs_lock);
> +	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> +	return true;
> +}
> +
> static fl_owner_t
> nfsd4_fl_get_owner(fl_owner_t owner)
> {
> @@ -6543,6 +6849,7 @@ static const struct lock_manager_operations nfsd_posix_mng_ops  = {
> 	.lm_notify = nfsd4_lm_notify,
> 	.lm_get_owner = nfsd4_fl_get_owner,
> 	.lm_put_owner = nfsd4_fl_put_owner,
> +	.lm_expire_lock = nfsd4_fl_expire_lock,

This applies to 1/2... You might choose a less NFSD-specific
name for the new lm_ method, such as lm_lock_conflict. I'm
guessing only NFSD is going to deal with a conflict by
/expiring/ something ...


> };
> 
> static inline void
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index e73bdbb1634a..7f52a79e0743 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -345,6 +345,8 @@ struct nfs4_client {
> #define NFSD4_CLIENT_UPCALL_LOCK	(5)	/* upcall serialization */
> #define NFSD4_CLIENT_CB_FLAG_MASK	(1 << NFSD4_CLIENT_CB_UPDATE | \
> 					 1 << NFSD4_CLIENT_CB_KILL)
> +#define NFSD4_COURTESY_CLIENT		(6)	/* be nice to expired client */
> +#define NFSD4_DESTROY_COURTESY_CLIENT	(7)
> 	unsigned long		cl_flags;
> 	const struct cred	*cl_cb_cred;
> 	struct rpc_clnt		*cl_cb_client;
> @@ -385,6 +387,12 @@ 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 */
> +	int			courtesy_client_expiry;
> +	/*
> +	 * used to synchronize access to NFSD4_COURTESY_CLIENT
> +	 * and NFSD4_DESTROY_COURTESY_CLIENT for race conditions.
> +	 */
> +	spinlock_t		cl_cs_lock;
> };
> 
> /* struct nfs4_client_reset
> -- 
> 2.9.5
> 

--
Chuck Lever

Dai Ngo Jan. 11, 2022, 1:03 a.m. UTC | #2

Thank you Chuck for your review, please see reply below:

On 1/10/22 3:17 PM, Chuck Lever III wrote:
> Hi Dai-
>
> Still getting the feel of the new approach, but I have
> made some comments inline...
>
>
>> On Jan 10, 2022, at 1:50 PM, Dai Ngo <[e-mail]> wrote:
>>
>> Currently an NFSv4 client must maintain its lease by using the at least
>> one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
>> a singleton SEQUENCE (4.1) at least once during each lease period. If the
>> client fails to renew the lease, for any reason, the Linux server expunges
>> the state tokens immediately upon detection of the "failure to renew the
>> lease" condition and begins returning NFS4ERR_EXPIRED if the client should
>> reconnect and attempt to use the (now) expired state.
>>
>> The default lease period for the Linux server is 90 seconds.  The typical
>> client cuts that in half and will issue a lease renewing operation every
>> 45 seconds. The 90 second lease period is very short considering the
>> potential for moderately long term network partitions.  A network partition
>> refers to any loss of network connectivity between the NFS client and the
>> NFS server, regardless of its root cause.  This includes NIC failures, NIC
>> driver bugs, network misconfigurations & administrative errors, routers &
>> switches crashing and/or having software updates applied, even down to
>> cables being physically pulled.  In most cases, these network failures are
>> transient, although the duration is unknown.
>>
>> A server which does not immediately expunge the state on lease expiration
>> is known as a Courteous Server.  A Courteous Server continues to recognize
>> previously generated state tokens as valid until conflict arises between
>> the expired state and the requests from another client, or the server
>> reboots.
>>
>> The initial implementation of the Courteous Server will do the following:
>>
>> . when the laundromat thread detects an expired client and if that client
>> still has established states on the Linux server and there is no waiters
>> for the client's locks then mark the client as a COURTESY_CLIENT and skip
>> destroying the client and all its states, otherwise destroy the client as
>> usual.
>>
>> . detects conflict of OPEN request with COURTESY_CLIENT, destroys the
>> expired client and all its states, skips the delegation recall then allows
>> the conflicting request to succeed.
>>
>> . detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
>> requests with COURTESY_CLIENT, destroys the expired client and all its
>> states then allows the conflicting request to succeed.
>>
>> . detects conflict of LOCK/LOCKT, NLM LOCK and TEST, and local locks
>> requests with COURTESY_CLIENT, destroys the expired client and all its
>> states then allows the conflicting request to succeed.
>>
>> Signed-off-by: Dai Ngo <[e-mail]>
>> ---
>> fs/nfsd/nfs4state.c | 323 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>> fs/nfsd/state.h     |   8 ++
>> 2 files changed, 323 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 3f4027a5de88..e7fa4da44835 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -125,6 +125,11 @@ 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 void laundromat_main(struct work_struct *);
>> +
>> +static const int courtesy_client_expiry = (24 * 60 * 60);	/* in secs */
>> +
>> static bool is_session_dead(struct nfsd4_session *ses)
>> {
>> 	return ses->se_flags & NFS4_SESSION_DEAD;
>> @@ -155,8 +160,10 @@ static __be32 get_client_locked(struct nfs4_client *clp)
>> 	return nfs_ok;
>> }
>>
>> -/* must be called under the client_lock */
>> +/* must be called under the client_lock
>> static inline void
>> +*/
>> +void
>> renew_client_locked(struct nfs4_client *clp)
>> {
>> 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>> @@ -172,7 +179,9 @@ renew_client_locked(struct nfs4_client *clp)
>>
>> 	list_move_tail(&clp->cl_lru, &nn->client_lru);
>> 	clp->cl_time = ktime_get_boottime_seconds();
>> +	clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> }
>> +EXPORT_SYMBOL_GPL(renew_client_locked);
> I don't see renew_client_locked() being called from outside
> fs/nfsd/nfs4state.c, and the patch doesn't add a global
> declaration.
>
> Please leave this function as "static inline void".

Fix in v10. I did it for debugging and forgot to remove it.
Test robot also reported the problem.

>
>
>> static void put_client_renew_locked(struct nfs4_client *clp)
>> {
>> @@ -1912,10 +1921,22 @@ find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid, struct net *net,
>> {
>> 	struct nfsd4_session *session;
>> 	__be32 status = nfserr_badsession;
>> +	struct nfs4_client *clp;
>>
>> 	session = __find_in_sessionid_hashtbl(sessionid, net);
>> 	if (!session)
>> 		goto out;
>> +	clp = session->se_client;
>> +	if (clp) {
>> +		spin_lock(&clp->cl_cs_lock);
>> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags)) {
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			session = NULL;
>> +			goto out;
>> +		}
>> +		clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> +		spin_unlock(&clp->cl_cs_lock);
>> +	}
>> 	status = nfsd4_get_session_locked(session);
>> 	if (status)
>> 		session = NULL;
>> @@ -1992,6 +2013,7 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
>> 	INIT_LIST_HEAD(&clp->async_copies);
>> 	spin_lock_init(&clp->async_lock);
>> 	spin_lock_init(&clp->cl_lock);
>> +	spin_lock_init(&clp->cl_cs_lock);
>> 	rpc_init_wait_queue(&clp->cl_cb_waitq, "Backchannel slot table");
>> 	return clp;
>> err_no_hashtbl:
>> @@ -2389,6 +2411,10 @@ static int client_info_show(struct seq_file *m, void *v)
>> 		seq_puts(m, "status: confirmed\n");
>> 	else
>> 		seq_puts(m, "status: unconfirmed\n");
>> +	seq_printf(m, "courtesy client: %s\n",
>> +		test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ? "yes" : "no");
>> +	seq_printf(m, "seconds from last renew: %lld\n",
>> +		ktime_get_boottime_seconds() - clp->cl_time);
>> 	seq_printf(m, "name: ");
>> 	seq_quote_mem(m, clp->cl_name.data, clp->cl_name.len);
>> 	seq_printf(m, "\nminor version: %d\n", clp->cl_minorversion);
>> @@ -2809,8 +2835,17 @@ find_clp_in_name_tree(struct xdr_netobj *name, struct rb_root *root)
>> 			node = node->rb_left;
>> 		else if (cmp < 0)
>> 			node = node->rb_right;
>> -		else
>> -			return clp;
>> +		else {
>> +			spin_lock(&clp->cl_cs_lock);
>> +			if (!test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
>> +					&clp->cl_flags)) {
>> +				clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				return clp;
>> +			}
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			return NULL;
>> +		}
>> 	}
>> 	return NULL;
>> }
>> @@ -2856,6 +2891,14 @@ find_client_in_id_table(struct list_head *tbl, clientid_t *clid, bool sessions)
>> 		if (same_clid(&clp->cl_clientid, clid)) {
>> 			if ((bool)clp->cl_minorversion != sessions)
>> 				return NULL;
>> +			spin_lock(&clp->cl_cs_lock);
>> +			if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
>> +					&clp->cl_flags)) {
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				continue;
>> +			}
>> +			clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> +			spin_unlock(&clp->cl_cs_lock);
> I'm wondering about the transition from COURTESY to active.
> Does that need to be synchronous with the client tracking
> database?

Currently when the client transits from active to COURTESY,
we do not remove the client record from the tracking database
so on the reverse we do not need to add it back.

I think this is something you and Bruce have been discussing
on whether when we should remove and add the client record from
the database when the client transits from active to COURTESY
and vice versa. With this patch we now expire the courtesy clients
asynchronously in the background so the overhead/delay from
removing the record from the database does not have any impact
on resolving conflicts.

>> 			renew_client_locked(clp);
>> 			return clp;
>> 		}
>> @@ -4662,6 +4705,36 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
>> 	nfsd4_run_cb(&dp->dl_recall);
>> }
>>
>> +/*
>> + * This function is called when a file is opened and there is a
>> + * delegation conflict with another client. If the other client
>> + * is a courtesy client then kick start the laundromat to destroy
>> + * it.
>> + */
>> +static bool
>> +nfsd_check_courtesy_client(struct nfs4_delegation *dp)
>> +{
>> +	struct svc_rqst *rqst;
>> +	struct nfs4_client *clp = dp->dl_recall.cb_clp;
>> +	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>> +
>> +	if (!i_am_nfsd())
>> +		goto out;
>> +	rqst = kthread_data(current);
>> +	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
>> +		return false;
>> +out:
>> +	spin_lock(&clp->cl_cs_lock);
>> +	if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
>> +		set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
>> +		spin_unlock(&clp->cl_cs_lock);
>> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> I'm not sure what is the purpose of the mod_delayed_work()
> here and below. What's the harm in leaving a DESTROYED
> nfs4_client around until the laundromat runs again? Won't
> it run every "grace period" seconds anyway?

I think this is a good idea. With the new approach of destroying
courtesy clients asynchronously in the background, I also don't
see a need to kick start the laundromat to run immediately. I will
make this change in v10 and make sure it works as expected.

>
> I didn't think we were depending on the laundromat to
> resolve edge case races, so if a call to a scheduler
> function isn't totally necessary in this code, I prefer
> that it be left out.
>
>
>> +		return true;
>> +	}
>> +	spin_unlock(&clp->cl_cs_lock);
>> +	return false;
>> +}
>> +
>> /* Called from break_lease() with i_lock held. */
>> static bool
>> nfsd_break_deleg_cb(struct file_lock *fl)
>> @@ -4670,6 +4743,8 @@ nfsd_break_deleg_cb(struct file_lock *fl)
>> 	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
>> 	struct nfs4_file *fp = dp->dl_stid.sc_file;
>>
>> +	if (nfsd_check_courtesy_client(dp))
>> +		return false;
>> 	trace_nfsd_cb_recall(&dp->dl_stid);
>>
>> 	/*
>> @@ -4912,7 +4987,128 @@ nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
>> 	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
>> }
>>
>> -static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>> +static bool
>> +__nfs4_check_access_deny_bmap(struct nfs4_ol_stateid *stp, u32 access,
>> +			bool share_access)
>> +{
>> +	if (share_access) {
>> +		if (!stp->st_deny_bmap)
>> +			return false;
>> +
>> +		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
>> +			(access & NFS4_SHARE_ACCESS_READ &&
>> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
>> +			(access & NFS4_SHARE_ACCESS_WRITE &&
>> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
>> +			return true;
>> +		}
>> +		return false;
>> +	}
>> +	if ((access & NFS4_SHARE_DENY_BOTH) ||
>> +		(access & NFS4_SHARE_DENY_READ &&
>> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
>> +		(access & NFS4_SHARE_DENY_WRITE &&
>> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
>> +		return true;
>> +	}
>> +	return false;
>> +}
>> +
>> +/*
>> + * Check all files belong to the specified client to determine if there is
>> + * any conflict with the specified access_mode/deny_mode of the file 'fp.
>> + *
>> + * If share_access is true then 'access' is the access mode. Check if
>> + * this access mode conflicts with current deny mode of the file.
>> + *
>> + * If share_access is false then 'access' the deny mode. Check if
>> + * this deny mode conflicts with current access mode of the file.
>> + */
>> +static bool
>> +nfs4_check_access_deny_bmap(struct nfs4_client *clp, struct nfs4_file *fp,
>> +		struct nfs4_ol_stateid *st, u32 access, bool share_access)
>> +{
>> +	int i;
>> +	struct nfs4_openowner *oo;
>> +	struct nfs4_stateowner *so, *tmp;
>> +	struct nfs4_ol_stateid *stp, *stmp;
>> +
>> +	spin_lock(&clp->cl_lock);
>> +	for (i = 0; i < OWNER_HASH_SIZE; i++) {
>> +		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
>> +					so_strhash) {
>> +			if (!so->so_is_open_owner)
>> +				continue;
>> +			oo = openowner(so);
>> +			list_for_each_entry_safe(stp, stmp,
>> +				&oo->oo_owner.so_stateids, st_perstateowner) {
>> +				if (stp == st || stp->st_stid.sc_file != fp)
>> +					continue;
>> +				if (__nfs4_check_access_deny_bmap(stp, access,
>> +							share_access)) {
>> +					spin_unlock(&clp->cl_lock);
>> +					return true;
>> +				}
>> +			}
>> +		}
>> +	}
>> +	spin_unlock(&clp->cl_lock);
>> +	return false;
>> +}
>> +
>> +/*
>> + * This function is called to check whether nfserr_share_denied should
>> + * be returning to client.
>> + *
>> + * access: is op_share_access if share_access is true.
>> + *	   Check if access mode, op_share_access, would conflict with
>> + *	   the current deny mode of the file 'fp'.
>> + * access: is op_share_deny if share_access is true.
>> + *	   Check if the deny mode, op_share_deny, would conflict with
>> + *	   current access of the file 'fp'.
>> + * stp:    skip checking this entry.
>> + *
>> + * Function returns:
>> + *	true  - access/deny mode conflict with courtesy client(s).
>> + *		Caller to return nfserr_jukebox while client(s) being expired.
>> + *	false - access/deny mode conflict with non-courtesy client.
>> + *		Caller to return nfserr_share_denied to client.
>> + */
>> +static bool
>> +nfs4_conflict_courtesy_clients(struct svc_rqst *rqstp, struct nfs4_file *fp,
>> +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
>> +{
>> +	struct nfs4_client *cl;
>> +	bool conflict = false;
>> +	int async_cnt = 0;
>> +	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
>> +
>> +	spin_lock(&nn->client_lock);
>> +	list_for_each_entry(cl, &nn->client_lru, cl_lru) {
>> +		if (!nfs4_check_access_deny_bmap(cl, fp, stp, access, share_access))
>> +			continue;
>> +		spin_lock(&cl->cl_cs_lock);
>> +		if (test_bit(NFSD4_COURTESY_CLIENT, &cl->cl_flags)) {
>> +			set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &cl->cl_flags);
>> +			async_cnt++;
> You can get rid of async_cnt. Just set conflict = true
> after unlocking cl_cs_lock. And again, maybe that
> mod_delayed_work() call site isn't necessary.

fix in v10.

>
>
>> +			spin_unlock(&cl->cl_cs_lock);
>> +			continue;
>> +		}
>> +		/* conflict with non-courtesy client */
>> +		spin_unlock(&cl->cl_cs_lock);
>> +		conflict = false;
>> +		break;
>> +	}
>> +	spin_unlock(&nn->client_lock);
>> +	if (async_cnt) {
>> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
>> +		conflict = true;
>> +	}
>> +	return conflict;
>> +}
>> +
>> +static __be32
>> +nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>> 		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
>> 		struct nfsd4_open *open)
>> {
>> @@ -4931,6 +5127,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>> 	status = nfs4_file_check_deny(fp, open->op_share_deny);
>> 	if (status != nfs_ok) {
>> 		spin_unlock(&fp->fi_lock);
>> +		if (status != nfserr_share_denied)
>> +			goto out;
>> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
>> +				stp, open->op_share_deny, false))
>> +			status = nfserr_jukebox;
>> 		goto out;
>> 	}
>>
>> @@ -4938,6 +5139,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>> 	status = nfs4_file_get_access(fp, open->op_share_access);
>> 	if (status != nfs_ok) {
>> 		spin_unlock(&fp->fi_lock);
>> +		if (status != nfserr_share_denied)
>> +			goto out;
>> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
>> +				stp, open->op_share_access, true))
>> +			status = nfserr_jukebox;
>> 		goto out;
>> 	}
>>
>> @@ -5572,6 +5778,47 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
>> }
>> #endif
>>
>> +static
>> +bool nfs4_anylock_conflict(struct nfs4_client *clp)
> This function assumes the caller holds cl_lock. That bears
> mentioning here in a comment. Convention suggests adding
> "_locked" to the function name too, just like
> renew_client_locked() above.

fix in v10.

>
> Also, nit: kernel style is either:
>
> static bool
> nfs4_anylock_conflict(
>
> or
>
> static bool nfs4_anylock_conflict(

fix in v10.

>
>
>> +{
>> +	int i;
>> +	struct nfs4_stateowner *so, *tmp;
>> +	struct nfs4_lockowner *lo;
>> +	struct nfs4_ol_stateid *stp;
>> +	struct nfs4_file *nf;
>> +	struct inode *ino;
>> +	struct file_lock_context *ctx;
>> +	struct file_lock *fl;
>> +
>> +	for (i = 0; i < OWNER_HASH_SIZE; i++) {
>> +		/* scan each lock owner */
>> +		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
>> +				so_strhash) {
>> +			if (so->so_is_open_owner)
>> +				continue;
>> +
>> +			/* scan lock states of this lock owner */
>> +			lo = lockowner(so);
>> +			list_for_each_entry(stp, &lo->lo_owner.so_stateids,
>> +					st_perstateowner) {
>> +				nf = stp->st_stid.sc_file;
>> +				ino = nf->fi_inode;
>> +				ctx = ino->i_flctx;
>> +				if (!ctx)
>> +					continue;
>> +				/* check each lock belongs to this lock state */
>> +				list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
>> +					if (fl->fl_owner != lo)
>> +						continue;
>> +					if (!list_empty(&fl->fl_blocked_requests))
>> +						return true;
>> +				}
>> +			}
>> +		}
>> +	}
>> +	return false;
>> +}
>> +
>> static time64_t
>> nfs4_laundromat(struct nfsd_net *nn)
>> {
>> @@ -5587,7 +5834,9 @@ nfs4_laundromat(struct nfsd_net *nn)
>> 	};
>> 	struct nfs4_cpntf_state *cps;
>> 	copy_stateid_t *cps_t;
>> +	struct nfs4_stid *stid;
>> 	int i;
>> +	int id;
>>
>> 	if (clients_still_reclaiming(nn)) {
>> 		lt.new_timeo = 0;
>> @@ -5608,8 +5857,41 @@ nfs4_laundromat(struct nfsd_net *nn)
>> 	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))
>> +		spin_lock(&clp->cl_cs_lock);
>> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags))
>> +			goto exp_client;
>> +		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
>> +			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
>> +				goto exp_client;
>> +			/*
>> +			 * after umount, v4.0 client is still around
>> +			 * waiting to be expired. Check again and if
>> +			 * it has no state then expire it.
>> +			 */
>> +			if (clp->cl_minorversion) {
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				continue;
>> +			}
>> +		}
>> +		if (!state_expired(&lt, clp->cl_time)) {
> Now that clients go from active -> COURTEOUS -> DESTROY,
> why is this check still necessary? If it truly is, a brief
> explanation/comment would help.

We still need this check to (1) transits client from active to
COURTESY state and (2) to stop the loop on client_lru since the
oldest entry is at the beginning of the list.

>
>> +			spin_unlock(&clp->cl_cs_lock);
>> 			break;
>> +		}
>> +		id = 0;
>> +		spin_lock(&clp->cl_lock);
>> +		stid = idr_get_next(&clp->cl_stateids, &id);
>> +		if (stid && !nfs4_anylock_conflict(clp)) {
>> +			/* client still has states */
>> +			spin_unlock(&clp->cl_lock);
>> +			clp->courtesy_client_expiry =
>> +				ktime_get_boottime_seconds() + courtesy_client_expiry;
>> +			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			continue;
>> +		}
>> +		spin_unlock(&clp->cl_lock);
>> +exp_client:
>> +		spin_unlock(&clp->cl_cs_lock);
>> 		if (mark_client_expired_locked(clp))
>> 			continue;
>> 		list_add(&clp->cl_lru, &reaplist);
>> @@ -5689,9 +5971,6 @@ 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 *);
>> -
> If the new mod_delayed_work() call sites aren't necessary,
> then these static definitions can be left here.

fix in v10.

>
>
>> static void
>> laundromat_main(struct work_struct *laundry)
>> {
>> @@ -6496,6 +6775,33 @@ nfs4_transform_lock_offset(struct file_lock *lock)
>> 		lock->fl_end = OFFSET_MAX;
>> }
>>
>> +/*
>> + * Return true if lock can be resolved by expiring
>> + * courtesy client else return false.
>> + */
> Since this function is invoked from outside of nfs4state.c,
> please turn the above comment into a kerneldoc comment, eg:
>
> /**
>   * nfsd4_fl_expire_lock - check if lock conflict can be resolved
>   * @fl: pointer to file_lock with a potential conflict
>   *
>   * Return values:
>   *   %true: No conflict exists
>   *   %false: Lock conflict can't be resolved

fix in v10.

>   */
>
>
>> +static bool
>> +nfsd4_fl_expire_lock(struct file_lock *fl)
>> +{
>> +	struct nfs4_lockowner *lo;
>> +	struct nfs4_client *clp;
>> +	struct nfsd_net *nn;
>> +
>> +	if (!fl)
>> +		return false;
>> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
>> +	clp = lo->lo_owner.so_client;
>> +	spin_lock(&clp->cl_cs_lock);
>> +	if (!test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
>> +		spin_unlock(&clp->cl_cs_lock);
>> +		return false;
>> +	}
>> +	nn = net_generic(clp->net, nfsd_net_id);
> Why is "nn =" inside the cl_cs_lock critical section here?
> I don't think that lock protects clp->net. Also, if the
> mod_delayed_work() call isn't needed here, then @nn can
> be removed too.

will remove nn, no longer need mod_delayed_work. fix in v10.

>
>
>> +	set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
>> +	spin_unlock(&clp->cl_cs_lock);
>> +	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
>> +	return true;
>> +}
>> +
>> static fl_owner_t
>> nfsd4_fl_get_owner(fl_owner_t owner)
>> {
>> @@ -6543,6 +6849,7 @@ static const struct lock_manager_operations nfsd_posix_mng_ops  = {
>> 	.lm_notify = nfsd4_lm_notify,
>> 	.lm_get_owner = nfsd4_fl_get_owner,
>> 	.lm_put_owner = nfsd4_fl_put_owner,
>> +	.lm_expire_lock = nfsd4_fl_expire_lock,
> This applies to 1/2... You might choose a less NFSD-specific
> name for the new lm_ method, such as lm_lock_conflict. I'm
> guessing only NFSD is going to deal with a conflict by
> /expiring/ something ...

will change from lm_expire_lock to lm_lock_conflict, fix in v10.

-Dai

>
>
>> };
>>
>> static inline void
>> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
>> index e73bdbb1634a..7f52a79e0743 100644
>> --- a/fs/nfsd/state.h
>> +++ b/fs/nfsd/state.h
>> @@ -345,6 +345,8 @@ struct nfs4_client {
>> #define NFSD4_CLIENT_UPCALL_LOCK	(5)	/* upcall serialization */
>> #define NFSD4_CLIENT_CB_FLAG_MASK	(1 << NFSD4_CLIENT_CB_UPDATE | \
>> 					 1 << NFSD4_CLIENT_CB_KILL)
>> +#define NFSD4_COURTESY_CLIENT		(6)	/* be nice to expired client */
>> +#define NFSD4_DESTROY_COURTESY_CLIENT	(7)
>> 	unsigned long		cl_flags;
>> 	const struct cred	*cl_cb_cred;
>> 	struct rpc_clnt		*cl_cb_client;
>> @@ -385,6 +387,12 @@ 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 */
>> +	int			courtesy_client_expiry;
>> +	/*
>> +	 * used to synchronize access to NFSD4_COURTESY_CLIENT
>> +	 * and NFSD4_DESTROY_COURTESY_CLIENT for race conditions.
>> +	 */
>> +	spinlock_t		cl_cs_lock;
>> };
>>
>> /* struct nfs4_client_reset
>> -- 
>> 2.9.5
>>
> --
> Chuck Lever
>
>
>

Chuck Lever Jan. 11, 2022, 3:49 p.m. UTC | #3

> On Jan 10, 2022, at 8:03 PM, Dai Ngo <[e-mail]> wrote:
> 
> Thank you Chuck for your review, please see reply below:
> 
> On 1/10/22 3:17 PM, Chuck Lever III wrote:
>> Hi Dai-
>> 
>> Still getting the feel of the new approach, but I have
>> made some comments inline...
>> 
>> 
>>> On Jan 10, 2022, at 1:50 PM, Dai Ngo <[e-mail]> wrote:
>>> 
>>> 	seq_printf(m, "\nminor version: %d\n", clp->cl_minorversion);
>>> @@ -2809,8 +2835,17 @@ find_clp_in_name_tree(struct xdr_netobj *name, struct rb_root *root)
>>> 			node = node->rb_left;
>>> 		else if (cmp < 0)
>>> 			node = node->rb_right;
>>> -		else
>>> -			return clp;
>>> +		else {
>>> +			spin_lock(&clp->cl_cs_lock);
>>> +			if (!test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
>>> +					&clp->cl_flags)) {
>>> +				clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>>> +				spin_unlock(&clp->cl_cs_lock);
>>> +				return clp;
>>> +			}
>>> +			spin_unlock(&clp->cl_cs_lock);
>>> +			return NULL;
>>> +		}
>>> 	}
>>> 	return NULL;
>>> }
>>> @@ -2856,6 +2891,14 @@ find_client_in_id_table(struct list_head *tbl, clientid_t *clid, bool sessions)
>>> 		if (same_clid(&clp->cl_clientid, clid)) {
>>> 			if ((bool)clp->cl_minorversion != sessions)
>>> 				return NULL;
>>> +			spin_lock(&clp->cl_cs_lock);
>>> +			if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
>>> +					&clp->cl_flags)) {
>>> +				spin_unlock(&clp->cl_cs_lock);
>>> +				continue;
>>> +			}
>>> +			clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>>> +			spin_unlock(&clp->cl_cs_lock);
>> I'm wondering about the transition from COURTESY to active.
>> Does that need to be synchronous with the client tracking
>> database?
> 
> Currently when the client transits from active to COURTESY,
> we do not remove the client record from the tracking database
> so on the reverse we do not need to add it back.
> 
> I think this is something you and Bruce have been discussing
> on whether when we should remove and add the client record from
> the database when the client transits from active to COURTESY
> and vice versa. With this patch we now expire the courtesy clients
> asynchronously in the background so the overhead/delay from
> removing the record from the database does not have any impact
> on resolving conflicts.

As I recall, our idea was to record the client as expired when
it transitions from active to COURTEOUS so that if the server
happens to reboot, it doesn't allow a courteous client to
reclaim locks the server may have already given to another
active client.

So I think the server needs to do an nfsdtrack upcall when
transitioning from active -> COURTEOUS to prevent that edge
case. That would happen only in the laundromat, right?

So when a COURTEOUS client comes back to the server, the server
will need to persistently record the transition from COURTEOUS
to active.

--
Chuck Lever

J. Bruce Fields Jan. 12, 2022, 6:53 p.m. UTC | #4

On Tue, Jan 11, 2022 at 03:49:19PM +0000, Chuck Lever III wrote:
> > On Jan 10, 2022, at 8:03 PM, Dai Ngo <[e-mail]> wrote:
> > I think this is something you and Bruce have been discussing
> > on whether when we should remove and add the client record from
> > the database when the client transits from active to COURTESY
> > and vice versa. With this patch we now expire the courtesy clients
> > asynchronously in the background so the overhead/delay from
> > removing the record from the database does not have any impact
> > on resolving conflicts.
> 
> As I recall, our idea was to record the client as expired when
> it transitions from active to COURTEOUS so that if the server
> happens to reboot, it doesn't allow a courteous client to
> reclaim locks the server may have already given to another
> active client.
> 
> So I think the server needs to do an nfsdtrack upcall when
> transitioning from active -> COURTEOUS to prevent that edge
> case. That would happen only in the laundromat, right?
> 
> So when a COURTEOUS client comes back to the server, the server
> will need to persistently record the transition from COURTEOUS
> to active.

Yep.  The bad case would be:

	- client A is marked DESTROY_COURTESY, client B is given A's
	  lock.
	- server goes down before laundromat thread removes the
	  DESTROY_COURTESY client.
	- client A's network comes back up.
	- server comes back up and starts grace period.

At this point, both A and B believe they have the lock.  Also both still
have nfsdcltrack records, so the server can't tell which is in the
right.

We can't start granting A's locks to B until we've recorded in stable
storage that A has expired.

What we'd like to do:

	- When a client transitions from active to courteous, it needs
	  to do nfsdcltrack upcall to expire it.
	- We mark client as COURTESY only after that upcall has
	  returned.
	- When the client comes back, we do an nfsdcltrack upcall to
	  mark it as active again.  We don't remove the COURTESY mark
	  until that's returned.

--b.

Dai Ngo Jan. 12, 2022, 6:56 p.m. UTC | #5

On 1/12/22 10:53 AM, Bruce Fields wrote:
> On Tue, Jan 11, 2022 at 03:49:19PM +0000, Chuck Lever III wrote:
>>> On Jan 10, 2022, at 8:03 PM, Dai Ngo <[e-mail]> wrote:
>>> I think this is something you and Bruce have been discussing
>>> on whether when we should remove and add the client record from
>>> the database when the client transits from active to COURTESY
>>> and vice versa. With this patch we now expire the courtesy clients
>>> asynchronously in the background so the overhead/delay from
>>> removing the record from the database does not have any impact
>>> on resolving conflicts.
>> As I recall, our idea was to record the client as expired when
>> it transitions from active to COURTEOUS so that if the server
>> happens to reboot, it doesn't allow a courteous client to
>> reclaim locks the server may have already given to another
>> active client.
>>
>> So I think the server needs to do an nfsdtrack upcall when
>> transitioning from active -> COURTEOUS to prevent that edge
>> case. That would happen only in the laundromat, right?
>>
>> So when a COURTEOUS client comes back to the server, the server
>> will need to persistently record the transition from COURTEOUS
>> to active.
> Yep.  The bad case would be:
>
> 	- client A is marked DESTROY_COURTESY, client B is given A's
> 	  lock.
> 	- server goes down before laundromat thread removes the
> 	  DESTROY_COURTESY client.
> 	- client A's network comes back up.
> 	- server comes back up and starts grace period.
>
> At this point, both A and B believe they have the lock.  Also both still
> have nfsdcltrack records, so the server can't tell which is in the
> right.
>
> We can't start granting A's locks to B until we've recorded in stable
> storage that A has expired.
>
> What we'd like to do:
>
> 	- When a client transitions from active to courteous, it needs
> 	  to do nfsdcltrack upcall to expire it.
> 	- We mark client as COURTESY only after that upcall has
> 	  returned.
> 	- When the client comes back, we do an nfsdcltrack upcall to
> 	  mark it as active again.  We don't remove the COURTESY mark
> 	  until that's returned.

Got it Bruce and Chuck, I will add this in v10.

Thanks,
-Dai

J. Bruce Fields Jan. 12, 2022, 7:40 p.m. UTC | #6

On Mon, Jan 10, 2022 at 10:50:53AM -0800, Dai Ngo wrote:
>  static time64_t
>  nfs4_laundromat(struct nfsd_net *nn)
>  {
> @@ -5587,7 +5834,9 @@ nfs4_laundromat(struct nfsd_net *nn)
>  	};
>  	struct nfs4_cpntf_state *cps;
>  	copy_stateid_t *cps_t;
> +	struct nfs4_stid *stid;
>  	int i;
> +	int id;
>  
>  	if (clients_still_reclaiming(nn)) {
>  		lt.new_timeo = 0;
> @@ -5608,8 +5857,41 @@ nfs4_laundromat(struct nfsd_net *nn)
>  	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))
> +		spin_lock(&clp->cl_cs_lock);
> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags))
> +			goto exp_client;
> +		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
> +			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
> +				goto exp_client;
> +			/*
> +			 * after umount, v4.0 client is still around
> +			 * waiting to be expired. Check again and if
> +			 * it has no state then expire it.
> +			 */
> +			if (clp->cl_minorversion) {
> +				spin_unlock(&clp->cl_cs_lock);
> +				continue;
> +			}

I'm not following that comment or that logic.

> +		}
> +		if (!state_expired(&lt, clp->cl_time)) {
> +			spin_unlock(&clp->cl_cs_lock);
>  			break;
> +		}
> +		id = 0;
> +		spin_lock(&clp->cl_lock);
> +		stid = idr_get_next(&clp->cl_stateids, &id);
> +		if (stid && !nfs4_anylock_conflict(clp)) {
> +			/* client still has states */

I'm a little confused by that comment.  I think what you just checked is
that the client has some state, *and* nobody is waiting for one of its
locks.  For me, that comment just conufses things.

> +			spin_unlock(&clp->cl_lock);

Is nn->client_lock enough to guarantee that the condition you just
checked still holds?  (Honest question, I'm not sure.)

> +			clp->courtesy_client_expiry =
> +				ktime_get_boottime_seconds() + courtesy_client_expiry;
> +			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
> +			spin_unlock(&clp->cl_cs_lock);
> +			continue;
> +		}
> +		spin_unlock(&clp->cl_lock);
> +exp_client:
> +		spin_unlock(&clp->cl_cs_lock);
>  		if (mark_client_expired_locked(clp))
>  			continue;
>  		list_add(&clp->cl_lru, &reaplist);

In general this loop is more complicated than the rest of the logic in
nfs4_laundromat(). I'd be looking for ways to simplify it and/or move some
of it into a helper function.

--b.

> @@ -5689,9 +5971,6 @@ nfs4_laundromat(struct nfsd_net *nn)
>  	return max_t(time64_t, lt.new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
>  }

J. Bruce Fields Jan. 12, 2022, 7:52 p.m. UTC | #7

On Mon, Jan 10, 2022 at 10:50:53AM -0800, Dai Ngo wrote:
> @@ -4912,7 +4987,128 @@ nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
>  	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
>  }
>  
> -static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
> +static bool
> +__nfs4_check_access_deny_bmap(struct nfs4_ol_stateid *stp, u32 access,
> +			bool share_access)
> +{
> +	if (share_access) {
> +		if (!stp->st_deny_bmap)
> +			return false;
> +
> +		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
> +			(access & NFS4_SHARE_ACCESS_READ &&
> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
> +			(access & NFS4_SHARE_ACCESS_WRITE &&
> +				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
> +			return true;
> +		}
> +		return false;
> +	}
> +	if ((access & NFS4_SHARE_DENY_BOTH) ||
> +		(access & NFS4_SHARE_DENY_READ &&
> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
> +		(access & NFS4_SHARE_DENY_WRITE &&
> +			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
> +		return true;
> +	}
> +	return false;
> +}
> +
> +/*
> + * Check all files belong to the specified client to determine if there is
> + * any conflict with the specified access_mode/deny_mode of the file 'fp.
> + *
> + * If share_access is true then 'access' is the access mode. Check if
> + * this access mode conflicts with current deny mode of the file.
> + *
> + * If share_access is false then 'access' the deny mode. Check if
> + * this deny mode conflicts with current access mode of the file.
> + */
> +static bool
> +nfs4_check_access_deny_bmap(struct nfs4_client *clp, struct nfs4_file *fp,
> +		struct nfs4_ol_stateid *st, u32 access, bool share_access)
> +{
> +	int i;
> +	struct nfs4_openowner *oo;
> +	struct nfs4_stateowner *so, *tmp;
> +	struct nfs4_ol_stateid *stp, *stmp;
> +
> +	spin_lock(&clp->cl_lock);
> +	for (i = 0; i < OWNER_HASH_SIZE; i++) {
> +		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
> +					so_strhash) {
> +			if (!so->so_is_open_owner)
> +				continue;
> +			oo = openowner(so);
> +			list_for_each_entry_safe(stp, stmp,
> +				&oo->oo_owner.so_stateids, st_perstateowner) {
> +				if (stp == st || stp->st_stid.sc_file != fp)
> +					continue;
> +				if (__nfs4_check_access_deny_bmap(stp, access,
> +							share_access)) {
> +					spin_unlock(&clp->cl_lock);
> +					return true;
> +				}
> +			}
> +		}
> +	}
> +	spin_unlock(&clp->cl_lock);
> +	return false;
> +}
> +
> +/*
> + * This function is called to check whether nfserr_share_denied should
> + * be returning to client.
> + *
> + * access: is op_share_access if share_access is true.
> + *	   Check if access mode, op_share_access, would conflict with
> + *	   the current deny mode of the file 'fp'.
> + * access: is op_share_deny if share_access is true.
> + *	   Check if the deny mode, op_share_deny, would conflict with
> + *	   current access of the file 'fp'.
> + * stp:    skip checking this entry.
> + *
> + * Function returns:
> + *	true  - access/deny mode conflict with courtesy client(s).
> + *		Caller to return nfserr_jukebox while client(s) being expired.
> + *	false - access/deny mode conflict with non-courtesy client.
> + *		Caller to return nfserr_share_denied to client.
> + */
> +static bool
> +nfs4_conflict_courtesy_clients(struct svc_rqst *rqstp, struct nfs4_file *fp,
> +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
> +{
> +	struct nfs4_client *cl;
> +	bool conflict = false;
> +	int async_cnt = 0;
> +	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> +
> +	spin_lock(&nn->client_lock);
> +	list_for_each_entry(cl, &nn->client_lru, cl_lru) {

This means we're manually searching through all the state of every
client each time we find a share conflict.

Well, maybe I'm OK with that.  Share conflicts are not the normal case.
(I'm not sure anyone actually uses them.)  So I guess I don't care if
that case is slow.

It's kind of a lot of code, though, I wish there were a way to simplify.

--b.

> +		if (!nfs4_check_access_deny_bmap(cl, fp, stp, access, share_access))
> +			continue;
> +		spin_lock(&cl->cl_cs_lock);
> +		if (test_bit(NFSD4_COURTESY_CLIENT, &cl->cl_flags)) {
> +			set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &cl->cl_flags);
> +			async_cnt++;
> +			spin_unlock(&cl->cl_cs_lock);
> +			continue;
> +		}
> +		/* conflict with non-courtesy client */
> +		spin_unlock(&cl->cl_cs_lock);
> +		conflict = false;
> +		break;
> +	}
> +	spin_unlock(&nn->client_lock);
> +	if (async_cnt) {
> +		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
> +		conflict = true;
> +	}
> +	return conflict;
> +}
> +
> +static __be32
> +nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>  		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
>  		struct nfsd4_open *open)
>  {
> @@ -4931,6 +5127,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>  	status = nfs4_file_check_deny(fp, open->op_share_deny);
>  	if (status != nfs_ok) {
>  		spin_unlock(&fp->fi_lock);
> +		if (status != nfserr_share_denied)
> +			goto out;
> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
> +				stp, open->op_share_deny, false))
> +			status = nfserr_jukebox;
>  		goto out;
>  	}
>  
> @@ -4938,6 +5139,11 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
>  	status = nfs4_file_get_access(fp, open->op_share_access);
>  	if (status != nfs_ok) {
>  		spin_unlock(&fp->fi_lock);
> +		if (status != nfserr_share_denied)
> +			goto out;
> +		if (nfs4_conflict_courtesy_clients(rqstp, fp,
> +				stp, open->op_share_access, true))
> +			status = nfserr_jukebox;
>  		goto out;
>  	}
>

Dai Ngo Jan. 13, 2022, 8:51 a.m. UTC | #8

On 1/12/22 11:40 AM, J. Bruce Fields wrote:
> On Mon, Jan 10, 2022 at 10:50:53AM -0800, Dai Ngo wrote:
>>   static time64_t
>>   nfs4_laundromat(struct nfsd_net *nn)
>>   {
>> @@ -5587,7 +5834,9 @@ nfs4_laundromat(struct nfsd_net *nn)
>>   	};
>>   	struct nfs4_cpntf_state *cps;
>>   	copy_stateid_t *cps_t;
>> +	struct nfs4_stid *stid;
>>   	int i;
>> +	int id;
>>   
>>   	if (clients_still_reclaiming(nn)) {
>>   		lt.new_timeo = 0;
>> @@ -5608,8 +5857,41 @@ nfs4_laundromat(struct nfsd_net *nn)
>>   	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))
>> +		spin_lock(&clp->cl_cs_lock);
>> +		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags))
>> +			goto exp_client;
>> +		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
>> +			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
>> +				goto exp_client;
>> +			/*
>> +			 * after umount, v4.0 client is still around
>> +			 * waiting to be expired. Check again and if
>> +			 * it has no state then expire it.
>> +			 */
>> +			if (clp->cl_minorversion) {
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				continue;
>> +			}
> I'm not following that comment or that logic.

When unmounting an export v4.0 client closes all its state. These state
are kept around on nn->close_lru to handle CLOSE replay. They remain on
the queue even after the client state (clp->cl_time) expired and became
courtesy client.

Eventually these state are freed by the laundromat when the state expire.
This is why we check v4.0 courtesy client again and if there is no state
associated with it then we expire the client.

>> +		}
>> +		if (!state_expired(&lt, clp->cl_time)) {
>> +			spin_unlock(&clp->cl_cs_lock);
>>   			break;
>> +		}
>> +		id = 0;
>> +		spin_lock(&clp->cl_lock);
>> +		stid = idr_get_next(&clp->cl_stateids, &id);
>> +		if (stid && !nfs4_anylock_conflict(clp)) {
>> +			/* client still has states */
> I'm a little confused by that comment.  I think what you just checked is
> that the client has some state, *and* nobody is waiting for one of its
> locks.  For me, that comment just conufses things.

will remove.

>
>> +			spin_unlock(&clp->cl_lock);
> Is nn->client_lock enough to guarantee that the condition you just
> checked still holds?  (Honest question, I'm not sure.)

nfs4_anylock_conflict_locked scans cl_ownerstr_hashtbl which is protected
by the cl_lock.

>
>> +			clp->courtesy_client_expiry =
>> +				ktime_get_boottime_seconds() + courtesy_client_expiry;
>> +			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			continue;
>> +		}
>> +		spin_unlock(&clp->cl_lock);
>> +exp_client:
>> +		spin_unlock(&clp->cl_cs_lock);
>>   		if (mark_client_expired_locked(clp))
>>   			continue;
>>   		list_add(&clp->cl_lru, &reaplist);
> In general this loop is more complicated than the rest of the logic in
> nfs4_laundromat(). I'd be looking for ways to simplify it and/or move some
> of it into a helper function.

I will move it to a function.

-Dai

J. Bruce Fields Jan. 13, 2022, 3:42 p.m. UTC | #9

On Thu, Jan 13, 2022 at 12:51:57AM -0800, [e-mail] wrote:
> 
> On 1/12/22 11:40 AM, J. Bruce Fields wrote:
> >On Mon, Jan 10, 2022 at 10:50:53AM -0800, Dai Ngo wrote:
> >>+		}
> >>+		if (!state_expired(&lt, clp->cl_time)) {
> >>+			spin_unlock(&clp->cl_cs_lock);
> >>  			break;
> >>+		}
> >>+		id = 0;
> >>+		spin_lock(&clp->cl_lock);
> >>+		stid = idr_get_next(&clp->cl_stateids, &id);
> >>+		if (stid && !nfs4_anylock_conflict(clp)) {
> >>+			/* client still has states */
> >I'm a little confused by that comment.  I think what you just checked is
> >that the client has some state, *and* nobody is waiting for one of its
> >locks.  For me, that comment just conufses things.
> 
> will remove.
> 
> >
> >>+			spin_unlock(&clp->cl_lock);
> >Is nn->client_lock enough to guarantee that the condition you just
> >checked still holds?  (Honest question, I'm not sure.)
> 
> nfs4_anylock_conflict_locked scans cl_ownerstr_hashtbl which is protected
> by the cl_lock.

That doesn't answer the question.  Which, I confess, was muddled (I
should have said "clp->cl_cs_lock", not "nn->client_lock".)

Let me try it a different way.  You just checked that the client has
some state, and that nobody is waiting for one of its locks.

After you drop the cl_lock, how do you know that both of those things
are still true?

--b.

Dai Ngo Jan. 13, 2022, 7:51 p.m. UTC | #10

On 1/13/22 7:42 AM, J. Bruce Fields wrote:
> On Thu, Jan 13, 2022 at 12:51:57AM -0800, [e-mail] wrote:
>> On 1/12/22 11:40 AM, J. Bruce Fields wrote:
>>> On Mon, Jan 10, 2022 at 10:50:53AM -0800, Dai Ngo wrote:
>>>> +		}
>>>> +		if (!state_expired(&lt, clp->cl_time)) {
>>>> +			spin_unlock(&clp->cl_cs_lock);
>>>>   			break;
>>>> +		}
>>>> +		id = 0;
>>>> +		spin_lock(&clp->cl_lock);
>>>> +		stid = idr_get_next(&clp->cl_stateids, &id);
>>>> +		if (stid && !nfs4_anylock_conflict(clp)) {
>>>> +			/* client still has states */
>>> I'm a little confused by that comment.  I think what you just checked is
>>> that the client has some state, *and* nobody is waiting for one of its
>>> locks.  For me, that comment just conufses things.
>> will remove.
>>
>>>> +			spin_unlock(&clp->cl_lock);
>>> Is nn->client_lock enough to guarantee that the condition you just
>>> checked still holds?  (Honest question, I'm not sure.)
>> nfs4_anylock_conflict_locked scans cl_ownerstr_hashtbl which is protected
>> by the cl_lock.
> That doesn't answer the question.  Which, I confess, was muddled (I
> should have said "clp->cl_cs_lock", not "nn->client_lock".)
>
> Let me try it a different way.  You just checked that the client has
> some state, and that nobody is waiting for one of its locks.
>
> After you drop the cl_lock, how do you know that both of those things
> are still true?

After we drop the lock, if the client now has no state then it just
remains in memory until the courtesy client timeout expires then we
get rid of it.

For the race condition of lock conflict, we use the client->cl_cs_lock
to synchronize the laundromat and and lm_lock_conflict/nfsd4_fl_lock_conflict.
If the locking thread acquires the cl_cs_lock before the laundromat does
then the thread will be blocked and laundromat detects there is blocker
and expires the client. If the laundromat acquires the cl_cs_lock first
then NFSD4_COURTESY_CLIENT is set and nfsd4_fl_lock_conflict detects
this flag and sets the client to NFSD4_DESTROY_COURTESY_CLIENT.

-Dai

Patch

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 3f4027a5de88..e7fa4da44835 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -125,6 +125,11 @@  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 void laundromat_main(struct work_struct *);
+
+static const int courtesy_client_expiry = (24 * 60 * 60);	/* in secs */
+
 static bool is_session_dead(struct nfsd4_session *ses)
 {
 	return ses->se_flags & NFS4_SESSION_DEAD;
@@ -155,8 +160,10 @@  static __be32 get_client_locked(struct nfs4_client *clp)
 	return nfs_ok;
 }
 
-/* must be called under the client_lock */
+/* must be called under the client_lock
 static inline void
+*/
+void
 renew_client_locked(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
@@ -172,7 +179,9 @@  renew_client_locked(struct nfs4_client *clp)
 
 	list_move_tail(&clp->cl_lru, &nn->client_lru);
 	clp->cl_time = ktime_get_boottime_seconds();
+	clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
 }
+EXPORT_SYMBOL_GPL(renew_client_locked);
 
 static void put_client_renew_locked(struct nfs4_client *clp)
 {
@@ -1912,10 +1921,22 @@  find_in_sessionid_hashtbl(struct nfs4_sessionid *sessionid, struct net *net,
 {
 	struct nfsd4_session *session;
 	__be32 status = nfserr_badsession;
+	struct nfs4_client *clp;
 
 	session = __find_in_sessionid_hashtbl(sessionid, net);
 	if (!session)
 		goto out;
+	clp = session->se_client;
+	if (clp) {
+		spin_lock(&clp->cl_cs_lock);
+		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags)) {
+			spin_unlock(&clp->cl_cs_lock);
+			session = NULL;
+			goto out;
+		}
+		clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+		spin_unlock(&clp->cl_cs_lock);
+	}
 	status = nfsd4_get_session_locked(session);
 	if (status)
 		session = NULL;
@@ -1992,6 +2013,7 @@  static struct nfs4_client *alloc_client(struct xdr_netobj name)
 	INIT_LIST_HEAD(&clp->async_copies);
 	spin_lock_init(&clp->async_lock);
 	spin_lock_init(&clp->cl_lock);
+	spin_lock_init(&clp->cl_cs_lock);
 	rpc_init_wait_queue(&clp->cl_cb_waitq, "Backchannel slot table");
 	return clp;
 err_no_hashtbl:
@@ -2389,6 +2411,10 @@  static int client_info_show(struct seq_file *m, void *v)
 		seq_puts(m, "status: confirmed\n");
 	else
 		seq_puts(m, "status: unconfirmed\n");
+	seq_printf(m, "courtesy client: %s\n",
+		test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags) ? "yes" : "no");
+	seq_printf(m, "seconds from last renew: %lld\n",
+		ktime_get_boottime_seconds() - clp->cl_time);
 	seq_printf(m, "name: ");
 	seq_quote_mem(m, clp->cl_name.data, clp->cl_name.len);
 	seq_printf(m, "\nminor version: %d\n", clp->cl_minorversion);
@@ -2809,8 +2835,17 @@  find_clp_in_name_tree(struct xdr_netobj *name, struct rb_root *root)
 			node = node->rb_left;
 		else if (cmp < 0)
 			node = node->rb_right;
-		else
-			return clp;
+		else {
+			spin_lock(&clp->cl_cs_lock);
+			if (!test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
+					&clp->cl_flags)) {
+				clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+				spin_unlock(&clp->cl_cs_lock);
+				return clp;
+			}
+			spin_unlock(&clp->cl_cs_lock);
+			return NULL;
+		}
 	}
 	return NULL;
 }
@@ -2856,6 +2891,14 @@  find_client_in_id_table(struct list_head *tbl, clientid_t *clid, bool sessions)
 		if (same_clid(&clp->cl_clientid, clid)) {
 			if ((bool)clp->cl_minorversion != sessions)
 				return NULL;
+			spin_lock(&clp->cl_cs_lock);
+			if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT,
+					&clp->cl_flags)) {
+				spin_unlock(&clp->cl_cs_lock);
+				continue;
+			}
+			clear_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+			spin_unlock(&clp->cl_cs_lock);
 			renew_client_locked(clp);
 			return clp;
 		}
@@ -4662,6 +4705,36 @@  static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
 	nfsd4_run_cb(&dp->dl_recall);
 }
 
+/*
+ * This function is called when a file is opened and there is a
+ * delegation conflict with another client. If the other client
+ * is a courtesy client then kick start the laundromat to destroy
+ * it.
+ */
+static bool
+nfsd_check_courtesy_client(struct nfs4_delegation *dp)
+{
+	struct svc_rqst *rqst;
+	struct nfs4_client *clp = dp->dl_recall.cb_clp;
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	if (!i_am_nfsd())
+		goto out;
+	rqst = kthread_data(current);
+	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
+		return false;
+out:
+	spin_lock(&clp->cl_cs_lock);
+	if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
+		set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
+		spin_unlock(&clp->cl_cs_lock);
+		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
+		return true;
+	}
+	spin_unlock(&clp->cl_cs_lock);
+	return false;
+}
+
 /* Called from break_lease() with i_lock held. */
 static bool
 nfsd_break_deleg_cb(struct file_lock *fl)
@@ -4670,6 +4743,8 @@  nfsd_break_deleg_cb(struct file_lock *fl)
 	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
 	struct nfs4_file *fp = dp->dl_stid.sc_file;
 
+	if (nfsd_check_courtesy_client(dp))
+		return false;
 	trace_nfsd_cb_recall(&dp->dl_stid);
 
 	/*
@@ -4912,7 +4987,128 @@  nfsd4_truncate(struct svc_rqst *rqstp, struct svc_fh *fh,
 	return nfsd_setattr(rqstp, fh, &iattr, 0, (time64_t)0);
 }
 
-static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
+static bool
+__nfs4_check_access_deny_bmap(struct nfs4_ol_stateid *stp, u32 access,
+			bool share_access)
+{
+	if (share_access) {
+		if (!stp->st_deny_bmap)
+			return false;
+
+		if ((stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_BOTH)) ||
+			(access & NFS4_SHARE_ACCESS_READ &&
+				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_READ)) ||
+			(access & NFS4_SHARE_ACCESS_WRITE &&
+				stp->st_deny_bmap & (1 << NFS4_SHARE_DENY_WRITE))) {
+			return true;
+		}
+		return false;
+	}
+	if ((access & NFS4_SHARE_DENY_BOTH) ||
+		(access & NFS4_SHARE_DENY_READ &&
+			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_READ)) ||
+		(access & NFS4_SHARE_DENY_WRITE &&
+			stp->st_access_bmap & (1 << NFS4_SHARE_ACCESS_WRITE))) {
+		return true;
+	}
+	return false;
+}
+
+/*
+ * Check all files belong to the specified client to determine if there is
+ * any conflict with the specified access_mode/deny_mode of the file 'fp.
+ *
+ * If share_access is true then 'access' is the access mode. Check if
+ * this access mode conflicts with current deny mode of the file.
+ *
+ * If share_access is false then 'access' the deny mode. Check if
+ * this deny mode conflicts with current access mode of the file.
+ */
+static bool
+nfs4_check_access_deny_bmap(struct nfs4_client *clp, struct nfs4_file *fp,
+		struct nfs4_ol_stateid *st, u32 access, bool share_access)
+{
+	int i;
+	struct nfs4_openowner *oo;
+	struct nfs4_stateowner *so, *tmp;
+	struct nfs4_ol_stateid *stp, *stmp;
+
+	spin_lock(&clp->cl_lock);
+	for (i = 0; i < OWNER_HASH_SIZE; i++) {
+		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
+					so_strhash) {
+			if (!so->so_is_open_owner)
+				continue;
+			oo = openowner(so);
+			list_for_each_entry_safe(stp, stmp,
+				&oo->oo_owner.so_stateids, st_perstateowner) {
+				if (stp == st || stp->st_stid.sc_file != fp)
+					continue;
+				if (__nfs4_check_access_deny_bmap(stp, access,
+							share_access)) {
+					spin_unlock(&clp->cl_lock);
+					return true;
+				}
+			}
+		}
+	}
+	spin_unlock(&clp->cl_lock);
+	return false;
+}
+
+/*
+ * This function is called to check whether nfserr_share_denied should
+ * be returning to client.
+ *
+ * access: is op_share_access if share_access is true.
+ *	   Check if access mode, op_share_access, would conflict with
+ *	   the current deny mode of the file 'fp'.
+ * access: is op_share_deny if share_access is true.
+ *	   Check if the deny mode, op_share_deny, would conflict with
+ *	   current access of the file 'fp'.
+ * stp:    skip checking this entry.
+ *
+ * Function returns:
+ *	true  - access/deny mode conflict with courtesy client(s).
+ *		Caller to return nfserr_jukebox while client(s) being expired.
+ *	false - access/deny mode conflict with non-courtesy client.
+ *		Caller to return nfserr_share_denied to client.
+ */
+static bool
+nfs4_conflict_courtesy_clients(struct svc_rqst *rqstp, struct nfs4_file *fp,
+		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
+{
+	struct nfs4_client *cl;
+	bool conflict = false;
+	int async_cnt = 0;
+	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+
+	spin_lock(&nn->client_lock);
+	list_for_each_entry(cl, &nn->client_lru, cl_lru) {
+		if (!nfs4_check_access_deny_bmap(cl, fp, stp, access, share_access))
+			continue;
+		spin_lock(&cl->cl_cs_lock);
+		if (test_bit(NFSD4_COURTESY_CLIENT, &cl->cl_flags)) {
+			set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &cl->cl_flags);
+			async_cnt++;
+			spin_unlock(&cl->cl_cs_lock);
+			continue;
+		}
+		/* conflict with non-courtesy client */
+		spin_unlock(&cl->cl_cs_lock);
+		conflict = false;
+		break;
+	}
+	spin_unlock(&nn->client_lock);
+	if (async_cnt) {
+		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
+		conflict = true;
+	}
+	return conflict;
+}
+
+static __be32
+nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 		struct svc_fh *cur_fh, struct nfs4_ol_stateid *stp,
 		struct nfsd4_open *open)
 {
@@ -4931,6 +5127,11 @@  static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 	status = nfs4_file_check_deny(fp, open->op_share_deny);
 	if (status != nfs_ok) {
 		spin_unlock(&fp->fi_lock);
+		if (status != nfserr_share_denied)
+			goto out;
+		if (nfs4_conflict_courtesy_clients(rqstp, fp,
+				stp, open->op_share_deny, false))
+			status = nfserr_jukebox;
 		goto out;
 	}
 
@@ -4938,6 +5139,11 @@  static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 	status = nfs4_file_get_access(fp, open->op_share_access);
 	if (status != nfs_ok) {
 		spin_unlock(&fp->fi_lock);
+		if (status != nfserr_share_denied)
+			goto out;
+		if (nfs4_conflict_courtesy_clients(rqstp, fp,
+				stp, open->op_share_access, true))
+			status = nfserr_jukebox;
 		goto out;
 	}
 
@@ -5572,6 +5778,47 @@  static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
 }
 #endif
 
+static
+bool nfs4_anylock_conflict(struct nfs4_client *clp)
+{
+	int i;
+	struct nfs4_stateowner *so, *tmp;
+	struct nfs4_lockowner *lo;
+	struct nfs4_ol_stateid *stp;
+	struct nfs4_file *nf;
+	struct inode *ino;
+	struct file_lock_context *ctx;
+	struct file_lock *fl;
+
+	for (i = 0; i < OWNER_HASH_SIZE; i++) {
+		/* scan each lock owner */
+		list_for_each_entry_safe(so, tmp, &clp->cl_ownerstr_hashtbl[i],
+				so_strhash) {
+			if (so->so_is_open_owner)
+				continue;
+
+			/* scan lock states of this lock owner */
+			lo = lockowner(so);
+			list_for_each_entry(stp, &lo->lo_owner.so_stateids,
+					st_perstateowner) {
+				nf = stp->st_stid.sc_file;
+				ino = nf->fi_inode;
+				ctx = ino->i_flctx;
+				if (!ctx)
+					continue;
+				/* check each lock belongs to this lock state */
+				list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
+					if (fl->fl_owner != lo)
+						continue;
+					if (!list_empty(&fl->fl_blocked_requests))
+						return true;
+				}
+			}
+		}
+	}
+	return false;
+}
+
 static time64_t
 nfs4_laundromat(struct nfsd_net *nn)
 {
@@ -5587,7 +5834,9 @@  nfs4_laundromat(struct nfsd_net *nn)
 	};
 	struct nfs4_cpntf_state *cps;
 	copy_stateid_t *cps_t;
+	struct nfs4_stid *stid;
 	int i;
+	int id;
 
 	if (clients_still_reclaiming(nn)) {
 		lt.new_timeo = 0;
@@ -5608,8 +5857,41 @@  nfs4_laundromat(struct nfsd_net *nn)
 	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))
+		spin_lock(&clp->cl_cs_lock);
+		if (test_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags))
+			goto exp_client;
+		if (test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
+			if (ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
+				goto exp_client;
+			/*
+			 * after umount, v4.0 client is still around
+			 * waiting to be expired. Check again and if
+			 * it has no state then expire it.
+			 */
+			if (clp->cl_minorversion) {
+				spin_unlock(&clp->cl_cs_lock);
+				continue;
+			}
+		}
+		if (!state_expired(&lt, clp->cl_time)) {
+			spin_unlock(&clp->cl_cs_lock);
 			break;
+		}
+		id = 0;
+		spin_lock(&clp->cl_lock);
+		stid = idr_get_next(&clp->cl_stateids, &id);
+		if (stid && !nfs4_anylock_conflict(clp)) {
+			/* client still has states */
+			spin_unlock(&clp->cl_lock);
+			clp->courtesy_client_expiry =
+				ktime_get_boottime_seconds() + courtesy_client_expiry;
+			set_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags);
+			spin_unlock(&clp->cl_cs_lock);
+			continue;
+		}
+		spin_unlock(&clp->cl_lock);
+exp_client:
+		spin_unlock(&clp->cl_cs_lock);
 		if (mark_client_expired_locked(clp))
 			continue;
 		list_add(&clp->cl_lru, &reaplist);
@@ -5689,9 +5971,6 @@  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
 laundromat_main(struct work_struct *laundry)
 {
@@ -6496,6 +6775,33 @@  nfs4_transform_lock_offset(struct file_lock *lock)
 		lock->fl_end = OFFSET_MAX;
 }
 
+/*
+ * Return true if lock can be resolved by expiring
+ * courtesy client else return false.
+ */
+static bool
+nfsd4_fl_expire_lock(struct file_lock *fl)
+{
+	struct nfs4_lockowner *lo;
+	struct nfs4_client *clp;
+	struct nfsd_net *nn;
+
+	if (!fl)
+		return false;
+	lo = (struct nfs4_lockowner *)fl->fl_owner;
+	clp = lo->lo_owner.so_client;
+	spin_lock(&clp->cl_cs_lock);
+	if (!test_bit(NFSD4_COURTESY_CLIENT, &clp->cl_flags)) {
+		spin_unlock(&clp->cl_cs_lock);
+		return false;
+	}
+	nn = net_generic(clp->net, nfsd_net_id);
+	set_bit(NFSD4_DESTROY_COURTESY_CLIENT, &clp->cl_flags);
+	spin_unlock(&clp->cl_cs_lock);
+	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
+	return true;
+}
+
 static fl_owner_t
 nfsd4_fl_get_owner(fl_owner_t owner)
 {
@@ -6543,6 +6849,7 @@  static const struct lock_manager_operations nfsd_posix_mng_ops  = {
 	.lm_notify = nfsd4_lm_notify,
 	.lm_get_owner = nfsd4_fl_get_owner,
 	.lm_put_owner = nfsd4_fl_put_owner,
+	.lm_expire_lock = nfsd4_fl_expire_lock,
 };
 
 static inline void
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e73bdbb1634a..7f52a79e0743 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -345,6 +345,8 @@  struct nfs4_client {
 #define NFSD4_CLIENT_UPCALL_LOCK	(5)	/* upcall serialization */
 #define NFSD4_CLIENT_CB_FLAG_MASK	(1 << NFSD4_CLIENT_CB_UPDATE | \
 					 1 << NFSD4_CLIENT_CB_KILL)
+#define NFSD4_COURTESY_CLIENT		(6)	/* be nice to expired client */
+#define NFSD4_DESTROY_COURTESY_CLIENT	(7)
 	unsigned long		cl_flags;
 	const struct cred	*cl_cb_cred;
 	struct rpc_clnt		*cl_cb_client;
@@ -385,6 +387,12 @@  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 */
+	int			courtesy_client_expiry;
+	/*
+	 * used to synchronize access to NFSD4_COURTESY_CLIENT
+	 * and NFSD4_DESTROY_COURTESY_CLIENT for race conditions.
+	 */
+	spinlock_t		cl_cs_lock;
 };
 
 /* struct nfs4_client_reset