[RFC,v13,4/4] nfsd: Initial implementation of NFSv4 Courteous Server

Commit Message

Dai Ngo Feb. 12, 2022, 6:12 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.

Problems such as hardware failures or administrative errors may cause
network partitions longer than the NFSv4 lease period. Our server currently
removes all client state as soon as a client fails to renew.

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 state on the Linux server and there is no waiters
for the client's locks then deletes the client persistent record and marks
the client as NFSD4_CLIENT_COURTESY and skips destroying the client and
all of its state, otherwise destroys the client as usual.

. Client persistent record is added to the client database when the
courtesy client reconnects and transits to normal client.

. Lock/delegation/share reversation conflict with courtesy client is
resolved by marking the courtesy client as NFSD4_CLIENT_DESTROY_COURTESY,
effectively disable it, then allow the current request to proceed
immediately.

. Courtesy client marked as NFSD4_CLIENT_DESTROY_COURTESY is not allowed to
reconnect to reuse itsstate. It is expired by the laundromat asynchronously
in the background.

Signed-off-by: Dai Ngo <[e-mail]>
---
 fs/nfsd/nfs4state.c | 440 +++++++++++++++++++++++++++++++++++++++++++++++++---
 fs/nfsd/nfsd.h      |   1 +
 fs/nfsd/state.h     |   6 +
 3 files changed, 424 insertions(+), 23 deletions(-)

Comments

Chuck Lever III Feb. 15, 2022, 5:17 p.m. UTC | #1

> On Feb 12, 2022, at 1:12 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.
> 
> Problems such as hardware failures or administrative errors may cause
> network partitions longer than the NFSv4 lease period. Our server currently
> removes all client state as soon as a client fails to renew.
> 
> 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 state on the Linux server and there is no waiters
> for the client's locks then deletes the client persistent record and marks
> the client as NFSD4_CLIENT_COURTESY and skips destroying the client and
> all of its state, otherwise destroys the client as usual.
> 
> . Client persistent record is added to the client database when the
> courtesy client reconnects and transits to normal client.
> 
> . Lock/delegation/share reversation conflict with courtesy client is
> resolved by marking the courtesy client as NFSD4_CLIENT_DESTROY_COURTESY,
> effectively disable it, then allow the current request to proceed
> immediately.
> 
> . Courtesy client marked as NFSD4_CLIENT_DESTROY_COURTESY is not allowed to
> reconnect to reuse itsstate. It is expired by the laundromat asynchronously
> in the background.
> 
> Signed-off-by: Dai Ngo <[e-mail]>
> ---
> fs/nfsd/nfs4state.c | 440 +++++++++++++++++++++++++++++++++++++++++++++++++---
> fs/nfsd/nfsd.h      |   1 +
> fs/nfsd/state.h     |   6 +
> 3 files changed, 424 insertions(+), 23 deletions(-)

Hi Dai-

I've applied the first three patches in this series for 5.18.
I also extracted a small fix from 4/4 that should be separate
and applied that too. When you resend, please rebase your
patch(es) on my public for-next branch.

I am still concerned about the increasing size of this patch
and its complexity in some areas. Generally we don't apply a
single large patch like this; the changes are broken down into
a series of much smaller updates. That makes review and later
debugging much easier for everyone.

Here's a rough example of how this /might/ be done:

  https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/log/?h=nfsd-courteous-server

Others might have different ideas of how to split this up.

I'm gaining more understanding of how this all works. The
sections dealing with share/deny access are still somewhat
outside my wheelhouse, so I'm depending on others (Jeff or
Bruce) to help out in those narrow areas. Breaking this
large patch into smaller ones will make it easier for them
to review this work surgically.

A few more comments below.


> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 32063733443d..b837ff97e097 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1935,10 +1935,33 @@ 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) {
> +		clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +		/* need to sync with thread resolving lock/deleg conflict */
> +		spin_lock(&clp->cl_cs_lock);
> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
> +			spin_unlock(&clp->cl_cs_lock);
> +			session = NULL;
> +			goto out;
> +		}
> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
> +			/*
> +			 * clear CLIENT_COURTESY flag to prevent it from being
> +			 * destroyed by thread trying to resolve conflicts.
> +			 */
> +			clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);

I plan to come back to this in a subsequent review once
some of the lower-hanging fruit has been harvested.


> +
> +			/* let caller knows it's courtesy client */
> +			set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +		}
> +		spin_unlock(&clp->cl_cs_lock);
> +	}
> 	status = nfsd4_get_session_locked(session);
> 	if (status)
> 		session = NULL;
> @@ -2008,6 +2031,7 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
> 	INIT_LIST_HEAD(&clp->cl_openowners);
> 	INIT_LIST_HEAD(&clp->cl_delegations);
> 	INIT_LIST_HEAD(&clp->cl_lru);
> +	INIT_LIST_HEAD(&clp->cl_cs_list);
> 	INIT_LIST_HEAD(&clp->cl_revoked);
> #ifdef CONFIG_NFSD_PNFS
> 	INIT_LIST_HEAD(&clp->cl_lo_states);
> @@ -2015,6 +2039,7 @@ 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:
> @@ -2412,6 +2437,10 @@ 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_CLIENT_COURTESY, &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);
> @@ -2832,8 +2861,22 @@ 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
> +		else {
> +			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +			/* sync with thread resolving lock/deleg conflict */
> +			spin_lock(&clp->cl_cs_lock);
> +			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
> +					&clp->cl_flags)) {
> +				spin_unlock(&clp->cl_cs_lock);
> +				return NULL;
> +			}
> +			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
> +				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
> +				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +			}
> +			spin_unlock(&clp->cl_cs_lock);
> 			return clp;
> +		}
> 	}
> 	return NULL;
> }
> @@ -2879,6 +2922,20 @@ 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;
> +
> +			/* need to sync with thread resolving lock/deleg conflict */
> +			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +			spin_lock(&clp->cl_cs_lock);
> +			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
> +					&clp->cl_flags)) {
> +				spin_unlock(&clp->cl_cs_lock);
> +				continue;
> +			}
> +			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
> +				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
> +				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
> +			}
> +			spin_unlock(&clp->cl_cs_lock);
> 			renew_client_locked(clp);
> 			return clp;
> 		}
> @@ -3118,6 +3175,14 @@ static __be32 copy_impl_id(struct nfs4_client *clp,
> 	return 0;
> }
> 
> +static void
> +nfsd4_discard_courtesy_clnt(struct nfs4_client *clp)
> +{
> +	spin_lock(&clp->cl_cs_lock);
> +	set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
> +	spin_unlock(&clp->cl_cs_lock);
> +}
> +
> __be32
> nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 		union nfsd4_op_u *u)
> @@ -3195,6 +3260,10 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 	/* Cases below refer to rfc 5661 section 18.35.4: */
> 	spin_lock(&nn->client_lock);
> 	conf = find_confirmed_client_by_name(&exid->clname, nn);
> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
> +		nfsd4_discard_courtesy_clnt(conf);
> +		conf = NULL;
> +	}
> 	if (conf) {
> 		bool creds_match = same_creds(&conf->cl_cred, &rqstp->rq_cred);
> 		bool verfs_match = same_verf(&verf, &conf->cl_verifier);
> @@ -3462,6 +3531,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
> 	spin_lock(&nn->client_lock);
> 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
> 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
> +		nfsd4_discard_courtesy_clnt(conf);
> +		conf = NULL;
> +	}

I'm seeing this bit of logic over and over again. I'm wondering
why "set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);" cannot
be done in the "find_confirmed_yada" functions? The "find" function
can even return NULL in that case, so changing all these call sites
should be totally unnecessary (except in a couple of cases where I
see there is additional logic at the call site).


> 	WARN_ON_ONCE(conf && unconf);
> 
> 	if (conf) {
> @@ -3493,6 +3566,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
> 			goto out_free_conn;
> 		}
> 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
> +		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &old->cl_flags)) {
> +			nfsd4_discard_courtesy_clnt(old);
> +			old = NULL;
> +		}
> 		if (old) {
> 			status = mark_client_expired_locked(old);
> 			if (status) {
> @@ -3631,6 +3708,7 @@ __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
> 	struct nfsd4_session *session;
> 	struct net *net = SVC_NET(rqstp);
> 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> +	struct nfs4_client *clp;
> 
> 	if (!nfsd4_last_compound_op(rqstp))
> 		return nfserr_not_only_op;
> @@ -3663,6 +3741,13 @@ __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
> 	nfsd4_init_conn(rqstp, conn, session);
> 	status = nfs_ok;
> out:
> +	clp = session->se_client;
> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
> +		if (status == nfs_ok)
> +			nfsd4_client_record_create(clp);
> +		else
> +			nfsd4_discard_courtesy_clnt(clp);
> +	}
> 	nfsd4_put_session(session);
> out_no_session:
> 	return status;
> @@ -3685,6 +3770,7 @@ nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
> 	int ref_held_by_me = 0;
> 	struct net *net = SVC_NET(r);
> 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> +	struct nfs4_client *clp;
> 
> 	status = nfserr_not_only_op;
> 	if (nfsd4_compound_in_session(cstate, sessionid)) {
> @@ -3697,6 +3783,13 @@ nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
> 	ses = find_in_sessionid_hashtbl(sessionid, net, &status);
> 	if (!ses)
> 		goto out_client_lock;
> +	clp = ses->se_client;
> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
> +		status = nfserr_badsession;
> +		nfsd4_discard_courtesy_clnt(clp);
> +		goto out_put_session;
> +	}
> +
> 	status = nfserr_wrong_cred;
> 	if (!nfsd4_mach_creds_match(ses->se_client, r))
> 		goto out_put_session;
> @@ -3801,7 +3894,7 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 	struct nfsd4_compoundres *resp = rqstp->rq_resp;
> 	struct xdr_stream *xdr = resp->xdr;
> 	struct nfsd4_session *session;
> -	struct nfs4_client *clp;
> +	struct nfs4_client *clp = NULL;
> 	struct nfsd4_slot *slot;
> 	struct nfsd4_conn *conn;
> 	__be32 status;
> @@ -3911,6 +4004,12 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 	if (conn)
> 		free_conn(conn);
> 	spin_unlock(&nn->client_lock);
> +	if (clp && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
> +		if (status == nfs_ok)
> +			nfsd4_client_record_create(clp);
> +		else
> +			nfsd4_discard_courtesy_clnt(clp);
> +	}
> 	return status;
> out_put_session:
> 	nfsd4_put_session_locked(session);
> @@ -3947,6 +4046,10 @@ nfsd4_destroy_clientid(struct svc_rqst *rqstp,
> 	spin_lock(&nn->client_lock);
> 	unconf = find_unconfirmed_client(&dc->clientid, true, nn);
> 	conf = find_confirmed_client(&dc->clientid, true, nn);
> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
> +		nfsd4_discard_courtesy_clnt(conf);
> +		conf = NULL;
> +	}
> 	WARN_ON_ONCE(conf && unconf);
> 
> 	if (conf) {
> @@ -4030,12 +4133,17 @@ nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 	struct nfs4_client	*unconf = NULL;
> 	__be32 			status;
> 	struct nfsd_net		*nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
> +	struct nfs4_client *cclient = NULL;
> 
> 	new = create_client(clname, rqstp, &clverifier);
> 	if (new == NULL)
> 		return nfserr_jukebox;
> 	spin_lock(&nn->client_lock);
> 	conf = find_confirmed_client_by_name(&clname, nn);
> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
> +		cclient = conf;
> +		conf = NULL;
> +	}
> 	if (conf && client_has_state(conf)) {
> 		status = nfserr_clid_inuse;
> 		if (clp_used_exchangeid(conf))
> @@ -4066,7 +4174,11 @@ nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> 	new = NULL;
> 	status = nfs_ok;
> out:
> +	if (cclient)
> +		unhash_client_locked(cclient);
> 	spin_unlock(&nn->client_lock);
> +	if (cclient)
> +		expire_client(cclient);
> 	if (new)
> 		free_client(new);
> 	if (unconf) {
> @@ -4096,6 +4208,10 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
> 	spin_lock(&nn->client_lock);
> 	conf = find_confirmed_client(clid, false, nn);
> 	unconf = find_unconfirmed_client(clid, false, nn);
> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
> +		nfsd4_discard_courtesy_clnt(conf);
> +		conf = NULL;
> +	}
> 	/*
> 	 * We try hard to give out unique clientid's, so if we get an
> 	 * attempt to confirm the same clientid with a different cred,
> @@ -4126,6 +4242,11 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
> 		nfsd4_change_callback(conf, &unconf->cl_cb_conn);
> 	} else {
> 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
> +		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT,
> +						&old->cl_flags)) {
> +			nfsd4_discard_courtesy_clnt(old);
> +			old = NULL;
> +		}
> 		if (old) {
> 			status = nfserr_clid_inuse;
> 			if (client_has_state(old)
> @@ -4711,18 +4832,41 @@ nfsd_break_deleg_cb(struct file_lock *fl)
> 	return ret;
> }
> 
> +/*
> + * Function returns true if lease conflict was resolved
> + * else returns false.
> + */
> static bool nfsd_breaker_owns_lease(struct file_lock *fl)
> {
> 	struct nfs4_delegation *dl = fl->fl_owner;
> 	struct svc_rqst *rqst;
> 	struct nfs4_client *clp;
> 
> +	clp = dl->dl_stid.sc_client;
> +
> +	/*
> +	 * need to sync with courtesy client trying to reconnect using
> +	 * the cl_cs_lock, nn->client_lock can not be used since this
> +	 * function is called with the fl_lck held.
> +	 */
> +	spin_lock(&clp->cl_cs_lock);
> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
> +		spin_unlock(&clp->cl_cs_lock);
> +		return true;
> +	}
> +	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
> +		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
> +		spin_unlock(&clp->cl_cs_lock);
> +		return true;
> +	}
> +	spin_unlock(&clp->cl_cs_lock);
> +
> 	if (!i_am_nfsd())
> -		return NULL;
> +		return false;

As noted in my general comments, this change (and the one
right below) is a stand-alone fix that I've pulled into a
separate patch and already applied.


> 	rqst = kthread_data(current);
> 	/* Note rq_prog == NFS_ACL_PROGRAM is also possible: */
> 	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
> -		return NULL;
> +		return false;
> 	clp = *(rqst->rq_lease_breaker);
> 	return dl->dl_stid.sc_client == clp;
> }
> @@ -4755,7 +4899,7 @@ static __be32 nfsd4_check_seqid(struct nfsd4_compound_state *cstate, struct nfs4
> }
> 
> static struct nfs4_client *lookup_clientid(clientid_t *clid, bool sessions,
> -						struct nfsd_net *nn)
> +			struct nfsd_net *nn)
> {
> 	struct nfs4_client *found;
> 
> @@ -4785,6 +4929,9 @@ static __be32 set_client(clientid_t *clid,
> 	cstate->clp = lookup_clientid(clid, false, nn);
> 	if (!cstate->clp)
> 		return nfserr_expired;
> +
> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &cstate->clp->cl_flags))
> +		nfsd4_client_record_create(cstate->clp);
> 	return nfs_ok;
> }
> 
> @@ -4937,9 +5084,89 @@ 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;
> +}
> +
> +/*
> + * This function is called to check whether nfserr_share_denied should
> + * be returning to client.

Nit: The Linux kernel contributor's documentation recommends
that short explanations should be written in the imperative,
like so:

"Check whether nfserr_share_denied should be returned."


> + *
> + * 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 false.
> + *	    Check if the deny mode, op_share_deny, would conflict with
> + *	    current access of the file 'fp'.
> + * stp:     skip checking this entry.
> + * new_stp: normal open, not open upgrade.
> + *
> + * Function returns:
> + *	true   - access/deny mode conflict with normal client.
> + *	false  - no conflict or conflict with courtesy client(s) is resolved.
> + */
> +static bool
> +nfs4_conflict_clients(struct nfs4_file *fp, bool new_stp,
> +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
> +{
> +	struct nfs4_ol_stateid *st;
> +	struct nfs4_client *cl;
> +	bool conflict = false;
> +
> +	lockdep_assert_held(&fp->fi_lock);
> +	list_for_each_entry(st, &fp->fi_stateids, st_perfile) {
> +		if (st->st_openstp || (st == stp && new_stp) ||
> +			(!nfs4_check_access_deny_bmap(st,
> +					access, share_access)))
> +			continue;
> +
> +		/* need to sync with courtesy client trying to reconnect */
> +		cl = st->st_stid.sc_client;
> +		spin_lock(&cl->cl_cs_lock);
> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags)) {
> +			spin_unlock(&cl->cl_cs_lock);
> +			continue;
> +		}
> +		if (test_bit(NFSD4_CLIENT_COURTESY, &cl->cl_flags)) {
> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags);
> +			spin_unlock(&cl->cl_cs_lock);
> +			continue;
> +		}
> +		/* conflict not caused by courtesy client */
> +		spin_unlock(&cl->cl_cs_lock);
> +		conflict = true;
> +		break;
> +	}
> +	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)
> +		struct nfsd4_open *open, bool new_stp)
> {
> 	struct nfsd_file *nf = NULL;
> 	__be32 status;
> @@ -4955,15 +5182,29 @@ 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);
> -		goto out;
> +		if (status != nfserr_share_denied) {
> +			spin_unlock(&fp->fi_lock);
> +			goto out;
> +		}
> +		if (nfs4_conflict_clients(fp, new_stp, stp,
> +				open->op_share_deny, false)) {
> +			spin_unlock(&fp->fi_lock);
> +			goto out;
> +		}
> 	}
> 
> 	/* set access to the file */
> 	status = nfs4_file_get_access(fp, open->op_share_access);
> 	if (status != nfs_ok) {
> -		spin_unlock(&fp->fi_lock);
> -		goto out;
> +		if (status != nfserr_share_denied) {
> +			spin_unlock(&fp->fi_lock);
> +			goto out;
> +		}
> +		if (nfs4_conflict_clients(fp, new_stp, stp,
> +				open->op_share_access, true)) {
> +			spin_unlock(&fp->fi_lock);
> +			goto out;
> +		}
> 	}
> 
> 	/* Set access bits in stateid */
> @@ -5014,7 +5255,7 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
> 	unsigned char old_deny_bmap = stp->st_deny_bmap;
> 
> 	if (!test_access(open->op_share_access, stp))
> -		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open);
> +		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open, false);
> 
> 	/* test and set deny mode */
> 	spin_lock(&fp->fi_lock);
> @@ -5363,7 +5604,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
> 			goto out;
> 		}
> 	} else {
> -		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
> +		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open, true);
> 		if (status) {
> 			stp->st_stid.sc_type = NFS4_CLOSED_STID;
> 			release_open_stateid(stp);
> @@ -5597,6 +5838,121 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
> }
> #endif
> 
> +static bool
> +nfs4_anylock_blocker(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;
> +
> +	spin_lock(&clp->cl_lock);
> +	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)) {
> +						spin_unlock(&clp->cl_lock);
> +						return true;
> +					}
> +				}
> +			}
> +		}
> +	}
> +	spin_unlock(&clp->cl_lock);
> +	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;
> +	struct list_head cslist;
> +
> +	INIT_LIST_HEAD(reaplist);
> +	INIT_LIST_HEAD(&cslist);
> +	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;
> +
> +		/* client expired */
> +		if (!client_has_state(clp)) {
> +			if (mark_client_expired_locked(clp))
> +				continue;
> +			list_add(&clp->cl_lru, reaplist);
> +			continue;
> +		}
> +
> +		/* expired client has state */
> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
> +			goto exp_client;
> +
> +		cour = test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
> +		if (cour &&
> +			ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
> +			goto exp_client;
> +
> +		if (nfs4_anylock_blocker(clp)) {
> +			/* expired client has state and has blocker. */
> +exp_client:
> +			if (mark_client_expired_locked(clp))
> +				continue;
> +			list_add(&clp->cl_lru, reaplist);
> +			continue;
> +		}
> +		/*
> +		 * Client expired and has state and has no blockers.
> +		 * If there is race condition with blockers, next time
> +		 * the laundromat runs it will catch it and expires
> +		 * the client.

Is this comment still true? I thought the laundromat now
turns such clients into courtesy clients.


> +		 */
> +		if (!cour) {
> +			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
> +			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
> +					NFSD_COURTESY_CLIENT_TIMEOUT;
> +			list_add(&clp->cl_cs_list, &cslist);

Can cl_lru (or some other existing list_head field)
be used instead of cl_cs_list?

I don't see anywhere that removes clp from cslist when
this processing is complete. Seems like you will get
list corruption next time the laundromat looks at
its list of nfs4_clients.


> +		}
> +	}
> +	spin_unlock(&nn->client_lock);
> +
> +	list_for_each_entry(clp, &cslist, cl_cs_list) {
> +		spin_lock(&clp->cl_cs_lock);
> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags) ||
> +			!test_bit(NFSD4_CLIENT_COURTESY,
> +					&clp->cl_flags)) {
> +			spin_unlock(&clp->cl_cs_lock);
> +			continue;
> +		}
> +		spin_unlock(&clp->cl_cs_lock);
> +		nfsd4_client_record_remove(clp);
> +	}

It wasn't clear to me what was going on here. I did a double
and triple take. But it looks like this is the spot where,
instead of removing the client record and destroying the
client, we just remove the client record and leave the
client in existence.

A more explanatory name for @cslist would help readers, IMO.

But maybe this code can be reorganized so that the high-level
decisions are made clear and the technical details are
shuffled off into helper functions. I don't have any specific
suggestions at this point, but I'm going to continue thinking
about how to make the laundromat a little less cluttered,
possibly as follow-on work.


> +}
> +
> static time64_t
> nfs4_laundromat(struct nfsd_net *nn)
> {
> @@ -5630,16 +5986,7 @@ nfs4_laundromat(struct nfsd_net *nn)
> 	}
> 	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);

There's already an "INIT_LIST_HEAD(&reaplist);" right above
this hunk that is repeated inside nfs4_get_client_reaplist().
Either one (but not both) can be removed.


> 	list_for_each_safe(pos, next, &reaplist) {
> 		clp = list_entry(pos, struct nfs4_client, cl_lru);
> 		trace_nfsd_clid_purged(&clp->cl_clientid);
> @@ -6021,6 +6368,15 @@ static __be32 find_cpntf_state(struct nfsd_net *nn, stateid_t *st,
> 	found = lookup_clientid(&cps->cp_p_clid, true, nn);
> 	if (!found)
> 		goto out;
> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &found->cl_flags)) {
> +		spin_lock(&found->cl_cs_lock);
> +		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &found->cl_flags);
> +		spin_unlock(&found->cl_cs_lock);
> +		if (atomic_dec_and_lock(&found->cl_rpc_users,
> +					&nn->client_lock))
> +			spin_unlock(&nn->client_lock);
> +		goto out;
> +	}
> 
> 	*stid = find_stateid_by_type(found, &cps->cp_p_stateid,
> 			NFS4_DELEG_STID|NFS4_OPEN_STID|NFS4_LOCK_STID);
> @@ -6525,6 +6881,43 @@ nfs4_transform_lock_offset(struct file_lock *lock)
> 		lock->fl_end = OFFSET_MAX;
> }
> 
> +/**
> + * nfsd4_fl_lock_expired - check if lock conflict can be resolved.
> + *
> + * @fl: pointer to file_lock with a potential conflict
> + * Return values:
> + *   %false: real conflict, lock conflict can not be resolved.
> + *   %true: no conflict, lock conflict was resolved.
> + *
> + * Note that this function is called while the flc_lock is held.
> + */
> +static bool
> +nfsd4_fl_lock_expired(struct file_lock *fl)

I'd prefer this guy to be named like the newer lm_ functions,
not the old fl_ functions. So: nfsd4_lm_lock_expired()

As an aside: I harp a lot on names and on patch descriptions.
Open source code is meant to enable users to make deep changes
to the software they use. They can't do that if the code is
obscure or poorly documented. Thus I view naming and
descriptions as nearly as critical as proper code licensing
for open source projects.

But also my memory is failing. The source code has to be
easily legible a year down the road when I have no
recollection of what it does or why. :-)


> +{
> +	struct nfs4_lockowner *lo;
> +	struct nfs4_client *clp;
> +	bool rc = false;
> +
> +	if (!fl)
> +		return false;
> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
> +	clp = lo->lo_owner.so_client;
> +
> +	/* need to sync with courtesy client trying to reconnect */
> +	spin_lock(&clp->cl_cs_lock);
> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
> +		rc = true;
> +	else {
> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
> +			rc =  true;
> +		} else
> +			rc =  false;

Couldn't you write it this way instead:

	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags))
		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
	rc = !!test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);

This is more a check to see whether I understand what's
going on rather than a request to change the patch.


> +	}
> +	spin_unlock(&clp->cl_cs_lock);
> +	return rc;
> +}
> +
> static fl_owner_t
> nfsd4_fl_get_owner(fl_owner_t owner)
> {
> @@ -6572,6 +6965,7 @@ 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_lock_expired = nfsd4_fl_lock_expired,
> };
> 
> static inline void
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index 3e5008b475ff..920fad00e2e4 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..80e565593d83 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -345,6 +345,9 @@ 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_CLIENT_COURTESY		(6)	/* be nice to expired client */

The comment is a little obtuse. If the client is
actually expired, then it will be ignored and
destroyed. Maybe "client is unreachable" ?


> +#define NFSD4_CLIENT_DESTROY_COURTESY	(7)

Maybe NFSD4_CLIENT_EXPIRE_COURTESY ? Dunno.


> +#define NFSD4_CLIENT_COURTESY_CLNT	(8)	/* used for lookup clientid/name */

The name CLIENT_COURTESY_CLNT doesn't make sense to me
when it appears in context. The comment doesn't clarify
it either. May I suggest:

#define NFSD4_CLIENT_RENEW_COURTESY	(8)	/* courtesy -> active */

Nit: If I'm reading the header file correctly, these new
definitions should /precede/ the definition of
NFSD4_CLIENT_CB_FLAG_MASK.


> 	unsigned long		cl_flags;
> 	const struct cred	*cl_cb_cred;
> 	struct rpc_clnt		*cl_cb_client;
> @@ -385,6 +388,9 @@ 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;

New fields need to be named cl_yada. "cl_courtesy_expiry"
maybe? Also, please make this a time64_t field.

Or, would it be possible instead to compute the expiry based
on the time of the last state renewal? Then a new field wouldn't
be necessary. I'm not sure, on balance, whether that would add
or reduce complexity.


> +	spinlock_t		cl_cs_lock;
> +	struct list_head	cl_cs_list;
> };
> 
> /* struct nfs4_client_reset
> -- 
> 2.9.5
> 

--
Chuck Lever

Dai Ngo Feb. 16, 2022, 9:56 a.m. UTC | #2

On 2/15/22 9:17 AM, Chuck Lever III wrote:
>
>> On Feb 12, 2022, at 1:12 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.
>>
>> Problems such as hardware failures or administrative errors may cause
>> network partitions longer than the NFSv4 lease period. Our server currently
>> removes all client state as soon as a client fails to renew.
>>
>> 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 state on the Linux server and there is no waiters
>> for the client's locks then deletes the client persistent record and marks
>> the client as NFSD4_CLIENT_COURTESY and skips destroying the client and
>> all of its state, otherwise destroys the client as usual.
>>
>> . Client persistent record is added to the client database when the
>> courtesy client reconnects and transits to normal client.
>>
>> . Lock/delegation/share reversation conflict with courtesy client is
>> resolved by marking the courtesy client as NFSD4_CLIENT_DESTROY_COURTESY,
>> effectively disable it, then allow the current request to proceed
>> immediately.
>>
>> . Courtesy client marked as NFSD4_CLIENT_DESTROY_COURTESY is not allowed to
>> reconnect to reuse itsstate. It is expired by the laundromat asynchronously
>> in the background.
>>
>> Signed-off-by: Dai Ngo <[e-mail]>
>> ---
>> fs/nfsd/nfs4state.c | 440 +++++++++++++++++++++++++++++++++++++++++++++++++---
>> fs/nfsd/nfsd.h      |   1 +
>> fs/nfsd/state.h     |   6 +
>> 3 files changed, 424 insertions(+), 23 deletions(-)
> Hi Dai-
>
> I've applied the first three patches in this series for 5.18.
> I also extracted a small fix from 4/4 that should be separate
> and applied that too. When you resend, please rebase your
> patch(es) on my public for-next branch.

ok.

>
> I am still concerned about the increasing size of this patch
> and its complexity in some areas. Generally we don't apply a
> single large patch like this; the changes are broken down into
> a series of much smaller updates. That makes review and later
> debugging much easier for everyone.
>
> Here's a rough example of how this /might/ be done:
>
>    https://git.kernel.org/pub/scm/linux/kernel/git/cel/linux.git/log/?h=nfsd-courteous-server

got it.

>
> Others might have different ideas of how to split this up.
>
> I'm gaining more understanding of how this all works. The
> sections dealing with share/deny access are still somewhat
> outside my wheelhouse, so I'm depending on others (Jeff or
> Bruce) to help out in those narrow areas. Breaking this
> large patch into smaller ones will make it easier for them
> to review this work surgically.
>
> A few more comments below.
>
>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 32063733443d..b837ff97e097 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -1935,10 +1935,33 @@ 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) {
>> +		clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +		/* need to sync with thread resolving lock/deleg conflict */
>> +		spin_lock(&clp->cl_cs_lock);
>> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			session = NULL;
>> +			goto out;
>> +		}
>> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>> +			/*
>> +			 * clear CLIENT_COURTESY flag to prevent it from being
>> +			 * destroyed by thread trying to resolve conflicts.
>> +			 */
>> +			clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
> I plan to come back to this in a subsequent review once
> some of the lower-hanging fruit has been harvested.
>
>
>> +
>> +			/* let caller knows it's courtesy client */
>> +			set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +		}
>> +		spin_unlock(&clp->cl_cs_lock);
>> +	}
>> 	status = nfsd4_get_session_locked(session);
>> 	if (status)
>> 		session = NULL;
>> @@ -2008,6 +2031,7 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
>> 	INIT_LIST_HEAD(&clp->cl_openowners);
>> 	INIT_LIST_HEAD(&clp->cl_delegations);
>> 	INIT_LIST_HEAD(&clp->cl_lru);
>> +	INIT_LIST_HEAD(&clp->cl_cs_list);
>> 	INIT_LIST_HEAD(&clp->cl_revoked);
>> #ifdef CONFIG_NFSD_PNFS
>> 	INIT_LIST_HEAD(&clp->cl_lo_states);
>> @@ -2015,6 +2039,7 @@ 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:
>> @@ -2412,6 +2437,10 @@ 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_CLIENT_COURTESY, &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);
>> @@ -2832,8 +2861,22 @@ 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
>> +		else {
>> +			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +			/* sync with thread resolving lock/deleg conflict */
>> +			spin_lock(&clp->cl_cs_lock);
>> +			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
>> +					&clp->cl_flags)) {
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				return NULL;
>> +			}
>> +			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>> +				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>> +				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +			}
>> +			spin_unlock(&clp->cl_cs_lock);
>> 			return clp;
>> +		}
>> 	}
>> 	return NULL;
>> }
>> @@ -2879,6 +2922,20 @@ 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;
>> +
>> +			/* need to sync with thread resolving lock/deleg conflict */
>> +			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +			spin_lock(&clp->cl_cs_lock);
>> +			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
>> +					&clp->cl_flags)) {
>> +				spin_unlock(&clp->cl_cs_lock);
>> +				continue;
>> +			}
>> +			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>> +				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>> +				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
>> +			}
>> +			spin_unlock(&clp->cl_cs_lock);
>> 			renew_client_locked(clp);
>> 			return clp;
>> 		}
>> @@ -3118,6 +3175,14 @@ static __be32 copy_impl_id(struct nfs4_client *clp,
>> 	return 0;
>> }
>>
>> +static void
>> +nfsd4_discard_courtesy_clnt(struct nfs4_client *clp)
>> +{
>> +	spin_lock(&clp->cl_cs_lock);
>> +	set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>> +	spin_unlock(&clp->cl_cs_lock);
>> +}
>> +
>> __be32
>> nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 		union nfsd4_op_u *u)
>> @@ -3195,6 +3260,10 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	/* Cases below refer to rfc 5661 section 18.35.4: */
>> 	spin_lock(&nn->client_lock);
>> 	conf = find_confirmed_client_by_name(&exid->clname, nn);
>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>> +		nfsd4_discard_courtesy_clnt(conf);
>> +		conf = NULL;
>> +	}
>> 	if (conf) {
>> 		bool creds_match = same_creds(&conf->cl_cred, &rqstp->rq_cred);
>> 		bool verfs_match = same_verf(&verf, &conf->cl_verifier);
>> @@ -3462,6 +3531,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
>> 	spin_lock(&nn->client_lock);
>> 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
>> 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>> +		nfsd4_discard_courtesy_clnt(conf);
>> +		conf = NULL;
>> +	}
> I'm seeing this bit of logic over and over again. I'm wondering
> why "set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);" cannot
> be done in the "find_confirmed_yada" functions? The "find" function
> can even return NULL in that case, so changing all these call sites
> should be totally unnecessary (except in a couple of cases where I
> see there is additional logic at the call site).

This is because not all consumers of find_client_confirm wants to
discard the courtesy client. The lookup_clientid needs to return the
courtesy client to its callers because one of the callers needs to
transit the courtesy client to an active client.

>
>
>> 	WARN_ON_ONCE(conf && unconf);
>>
>> 	if (conf) {
>> @@ -3493,6 +3566,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
>> 			goto out_free_conn;
>> 		}
>> 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
>> +		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &old->cl_flags)) {
>> +			nfsd4_discard_courtesy_clnt(old);
>> +			old = NULL;
>> +		}
>> 		if (old) {
>> 			status = mark_client_expired_locked(old);
>> 			if (status) {
>> @@ -3631,6 +3708,7 @@ __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
>> 	struct nfsd4_session *session;
>> 	struct net *net = SVC_NET(rqstp);
>> 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>> +	struct nfs4_client *clp;
>>
>> 	if (!nfsd4_last_compound_op(rqstp))
>> 		return nfserr_not_only_op;
>> @@ -3663,6 +3741,13 @@ __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
>> 	nfsd4_init_conn(rqstp, conn, session);
>> 	status = nfs_ok;
>> out:
>> +	clp = session->se_client;
>> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
>> +		if (status == nfs_ok)
>> +			nfsd4_client_record_create(clp);
>> +		else
>> +			nfsd4_discard_courtesy_clnt(clp);
>> +	}
>> 	nfsd4_put_session(session);
>> out_no_session:
>> 	return status;
>> @@ -3685,6 +3770,7 @@ nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
>> 	int ref_held_by_me = 0;
>> 	struct net *net = SVC_NET(r);
>> 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
>> +	struct nfs4_client *clp;
>>
>> 	status = nfserr_not_only_op;
>> 	if (nfsd4_compound_in_session(cstate, sessionid)) {
>> @@ -3697,6 +3783,13 @@ nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
>> 	ses = find_in_sessionid_hashtbl(sessionid, net, &status);
>> 	if (!ses)
>> 		goto out_client_lock;
>> +	clp = ses->se_client;
>> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
>> +		status = nfserr_badsession;
>> +		nfsd4_discard_courtesy_clnt(clp);
>> +		goto out_put_session;
>> +	}
>> +
>> 	status = nfserr_wrong_cred;
>> 	if (!nfsd4_mach_creds_match(ses->se_client, r))
>> 		goto out_put_session;
>> @@ -3801,7 +3894,7 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	struct nfsd4_compoundres *resp = rqstp->rq_resp;
>> 	struct xdr_stream *xdr = resp->xdr;
>> 	struct nfsd4_session *session;
>> -	struct nfs4_client *clp;
>> +	struct nfs4_client *clp = NULL;
>> 	struct nfsd4_slot *slot;
>> 	struct nfsd4_conn *conn;
>> 	__be32 status;
>> @@ -3911,6 +4004,12 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	if (conn)
>> 		free_conn(conn);
>> 	spin_unlock(&nn->client_lock);
>> +	if (clp && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
>> +		if (status == nfs_ok)
>> +			nfsd4_client_record_create(clp);
>> +		else
>> +			nfsd4_discard_courtesy_clnt(clp);
>> +	}
>> 	return status;
>> out_put_session:
>> 	nfsd4_put_session_locked(session);
>> @@ -3947,6 +4046,10 @@ nfsd4_destroy_clientid(struct svc_rqst *rqstp,
>> 	spin_lock(&nn->client_lock);
>> 	unconf = find_unconfirmed_client(&dc->clientid, true, nn);
>> 	conf = find_confirmed_client(&dc->clientid, true, nn);
>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>> +		nfsd4_discard_courtesy_clnt(conf);
>> +		conf = NULL;
>> +	}
>> 	WARN_ON_ONCE(conf && unconf);
>>
>> 	if (conf) {
>> @@ -4030,12 +4133,17 @@ nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	struct nfs4_client	*unconf = NULL;
>> 	__be32 			status;
>> 	struct nfsd_net		*nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
>> +	struct nfs4_client *cclient = NULL;
>>
>> 	new = create_client(clname, rqstp, &clverifier);
>> 	if (new == NULL)
>> 		return nfserr_jukebox;
>> 	spin_lock(&nn->client_lock);
>> 	conf = find_confirmed_client_by_name(&clname, nn);
>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>> +		cclient = conf;
>> +		conf = NULL;
>> +	}
>> 	if (conf && client_has_state(conf)) {
>> 		status = nfserr_clid_inuse;
>> 		if (clp_used_exchangeid(conf))
>> @@ -4066,7 +4174,11 @@ nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>> 	new = NULL;
>> 	status = nfs_ok;
>> out:
>> +	if (cclient)
>> +		unhash_client_locked(cclient);
>> 	spin_unlock(&nn->client_lock);
>> +	if (cclient)
>> +		expire_client(cclient);
>> 	if (new)
>> 		free_client(new);
>> 	if (unconf) {
>> @@ -4096,6 +4208,10 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
>> 	spin_lock(&nn->client_lock);
>> 	conf = find_confirmed_client(clid, false, nn);
>> 	unconf = find_unconfirmed_client(clid, false, nn);
>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>> +		nfsd4_discard_courtesy_clnt(conf);
>> +		conf = NULL;
>> +	}
>> 	/*
>> 	 * We try hard to give out unique clientid's, so if we get an
>> 	 * attempt to confirm the same clientid with a different cred,
>> @@ -4126,6 +4242,11 @@ nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
>> 		nfsd4_change_callback(conf, &unconf->cl_cb_conn);
>> 	} else {
>> 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
>> +		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT,
>> +						&old->cl_flags)) {
>> +			nfsd4_discard_courtesy_clnt(old);
>> +			old = NULL;
>> +		}
>> 		if (old) {
>> 			status = nfserr_clid_inuse;
>> 			if (client_has_state(old)
>> @@ -4711,18 +4832,41 @@ nfsd_break_deleg_cb(struct file_lock *fl)
>> 	return ret;
>> }
>>
>> +/*
>> + * Function returns true if lease conflict was resolved
>> + * else returns false.
>> + */
>> static bool nfsd_breaker_owns_lease(struct file_lock *fl)
>> {
>> 	struct nfs4_delegation *dl = fl->fl_owner;
>> 	struct svc_rqst *rqst;
>> 	struct nfs4_client *clp;
>>
>> +	clp = dl->dl_stid.sc_client;
>> +
>> +	/*
>> +	 * need to sync with courtesy client trying to reconnect using
>> +	 * the cl_cs_lock, nn->client_lock can not be used since this
>> +	 * function is called with the fl_lck held.
>> +	 */
>> +	spin_lock(&clp->cl_cs_lock);
>> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
>> +		spin_unlock(&clp->cl_cs_lock);
>> +		return true;
>> +	}
>> +	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>> +		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>> +		spin_unlock(&clp->cl_cs_lock);
>> +		return true;
>> +	}
>> +	spin_unlock(&clp->cl_cs_lock);
>> +
>> 	if (!i_am_nfsd())
>> -		return NULL;
>> +		return false;
> As noted in my general comments, this change (and the one
> right below) is a stand-alone fix that I've pulled into a
> separate patch and already applied.

ok.

>
>
>> 	rqst = kthread_data(current);
>> 	/* Note rq_prog == NFS_ACL_PROGRAM is also possible: */
>> 	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
>> -		return NULL;
>> +		return false;
>> 	clp = *(rqst->rq_lease_breaker);
>> 	return dl->dl_stid.sc_client == clp;
>> }
>> @@ -4755,7 +4899,7 @@ static __be32 nfsd4_check_seqid(struct nfsd4_compound_state *cstate, struct nfs4
>> }
>>
>> static struct nfs4_client *lookup_clientid(clientid_t *clid, bool sessions,
>> -						struct nfsd_net *nn)
>> +			struct nfsd_net *nn)
>> {
>> 	struct nfs4_client *found;
>>
>> @@ -4785,6 +4929,9 @@ static __be32 set_client(clientid_t *clid,
>> 	cstate->clp = lookup_clientid(clid, false, nn);
>> 	if (!cstate->clp)
>> 		return nfserr_expired;
>> +
>> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &cstate->clp->cl_flags))
>> +		nfsd4_client_record_create(cstate->clp);
>> 	return nfs_ok;
>> }
>>
>> @@ -4937,9 +5084,89 @@ 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;
>> +}
>> +
>> +/*
>> + * This function is called to check whether nfserr_share_denied should
>> + * be returning to client.
> Nit: The Linux kernel contributor's documentation recommends
> that short explanations should be written in the imperative,
> like so:
>
> "Check whether nfserr_share_denied should be returned."

fix in v14.

>
>
>> + *
>> + * 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 false.
>> + *	    Check if the deny mode, op_share_deny, would conflict with
>> + *	    current access of the file 'fp'.
>> + * stp:     skip checking this entry.
>> + * new_stp: normal open, not open upgrade.
>> + *
>> + * Function returns:
>> + *	true   - access/deny mode conflict with normal client.
>> + *	false  - no conflict or conflict with courtesy client(s) is resolved.
>> + */
>> +static bool
>> +nfs4_conflict_clients(struct nfs4_file *fp, bool new_stp,
>> +		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
>> +{
>> +	struct nfs4_ol_stateid *st;
>> +	struct nfs4_client *cl;
>> +	bool conflict = false;
>> +
>> +	lockdep_assert_held(&fp->fi_lock);
>> +	list_for_each_entry(st, &fp->fi_stateids, st_perfile) {
>> +		if (st->st_openstp || (st == stp && new_stp) ||
>> +			(!nfs4_check_access_deny_bmap(st,
>> +					access, share_access)))
>> +			continue;
>> +
>> +		/* need to sync with courtesy client trying to reconnect */
>> +		cl = st->st_stid.sc_client;
>> +		spin_lock(&cl->cl_cs_lock);
>> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags)) {
>> +			spin_unlock(&cl->cl_cs_lock);
>> +			continue;
>> +		}
>> +		if (test_bit(NFSD4_CLIENT_COURTESY, &cl->cl_flags)) {
>> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags);
>> +			spin_unlock(&cl->cl_cs_lock);
>> +			continue;
>> +		}
>> +		/* conflict not caused by courtesy client */
>> +		spin_unlock(&cl->cl_cs_lock);
>> +		conflict = true;
>> +		break;
>> +	}
>> +	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)
>> +		struct nfsd4_open *open, bool new_stp)
>> {
>> 	struct nfsd_file *nf = NULL;
>> 	__be32 status;
>> @@ -4955,15 +5182,29 @@ 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);
>> -		goto out;
>> +		if (status != nfserr_share_denied) {
>> +			spin_unlock(&fp->fi_lock);
>> +			goto out;
>> +		}
>> +		if (nfs4_conflict_clients(fp, new_stp, stp,
>> +				open->op_share_deny, false)) {
>> +			spin_unlock(&fp->fi_lock);
>> +			goto out;
>> +		}
>> 	}
>>
>> 	/* set access to the file */
>> 	status = nfs4_file_get_access(fp, open->op_share_access);
>> 	if (status != nfs_ok) {
>> -		spin_unlock(&fp->fi_lock);
>> -		goto out;
>> +		if (status != nfserr_share_denied) {
>> +			spin_unlock(&fp->fi_lock);
>> +			goto out;
>> +		}
>> +		if (nfs4_conflict_clients(fp, new_stp, stp,
>> +				open->op_share_access, true)) {
>> +			spin_unlock(&fp->fi_lock);
>> +			goto out;
>> +		}
>> 	}
>>
>> 	/* Set access bits in stateid */
>> @@ -5014,7 +5255,7 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
>> 	unsigned char old_deny_bmap = stp->st_deny_bmap;
>>
>> 	if (!test_access(open->op_share_access, stp))
>> -		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open);
>> +		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open, false);
>>
>> 	/* test and set deny mode */
>> 	spin_lock(&fp->fi_lock);
>> @@ -5363,7 +5604,7 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
>> 			goto out;
>> 		}
>> 	} else {
>> -		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
>> +		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open, true);
>> 		if (status) {
>> 			stp->st_stid.sc_type = NFS4_CLOSED_STID;
>> 			release_open_stateid(stp);
>> @@ -5597,6 +5838,121 @@ static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
>> }
>> #endif
>>
>> +static bool
>> +nfs4_anylock_blocker(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;
>> +
>> +	spin_lock(&clp->cl_lock);
>> +	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)) {
>> +						spin_unlock(&clp->cl_lock);
>> +						return true;
>> +					}
>> +				}
>> +			}
>> +		}
>> +	}
>> +	spin_unlock(&clp->cl_lock);
>> +	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;
>> +	struct list_head cslist;
>> +
>> +	INIT_LIST_HEAD(reaplist);
>> +	INIT_LIST_HEAD(&cslist);
>> +	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;
>> +
>> +		/* client expired */
>> +		if (!client_has_state(clp)) {
>> +			if (mark_client_expired_locked(clp))
>> +				continue;
>> +			list_add(&clp->cl_lru, reaplist);
>> +			continue;
>> +		}
>> +
>> +		/* expired client has state */
>> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
>> +			goto exp_client;
>> +
>> +		cour = test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>> +		if (cour &&
>> +			ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
>> +			goto exp_client;
>> +
>> +		if (nfs4_anylock_blocker(clp)) {
>> +			/* expired client has state and has blocker. */
>> +exp_client:
>> +			if (mark_client_expired_locked(clp))
>> +				continue;
>> +			list_add(&clp->cl_lru, reaplist);
>> +			continue;
>> +		}
>> +		/*
>> +		 * Client expired and has state and has no blockers.
>> +		 * If there is race condition with blockers, next time
>> +		 * the laundromat runs it will catch it and expires
>> +		 * the client.
> Is this comment still true? I thought the laundromat now
> turns such clients into courtesy clients.

Yes. The laundromat will turn expired client with no blockers
into courtesy client. I will replace:

'Client expired and has state and has no blockers.'
with
'Client expired and has state and has no blockers, transits
client to courtesy client'.

>
>
>> +		 */
>> +		if (!cour) {
>> +			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>> +			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
>> +					NFSD_COURTESY_CLIENT_TIMEOUT;
>> +			list_add(&clp->cl_cs_list, &cslist);
> Can cl_lru (or some other existing list_head field)
> be used instead of cl_cs_list?

The cl_lru is used for clients to be expired, the cl_cs_list
is used for courtesy clients and they are treated differently.
Merging two lists together means we have to re-scan the cl_lru
list again to pick the courtesy clients and take appropriate
action which is not very efficient and clean. I don't see any
existing list_head field can be used for this.

>
> I don't see anywhere that removes clp from cslist when
> this processing is complete. Seems like you will get
> list corruption next time the laundromat looks at
> its list of nfs4_clients.

We re-initialize the list head before every time the laundromat
runs so there is no need to remove the entries once we're done.

>
>
>> +		}
>> +	}
>> +	spin_unlock(&nn->client_lock);
>> +
>> +	list_for_each_entry(clp, &cslist, cl_cs_list) {
>> +		spin_lock(&clp->cl_cs_lock);
>> +		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags) ||
>> +			!test_bit(NFSD4_CLIENT_COURTESY,
>> +					&clp->cl_flags)) {
>> +			spin_unlock(&clp->cl_cs_lock);
>> +			continue;
>> +		}
>> +		spin_unlock(&clp->cl_cs_lock);
>> +		nfsd4_client_record_remove(clp);
>> +	}
> It wasn't clear to me what was going on here. I did a double
> and triple take. But it looks like this is the spot where,
> instead of removing the client record and destroying the
> client, we just remove the client record and leave the
> client in existence.

This block of code is to handle the race condition where the client
was set to NFSD4_CLIENT_COURTESY and the client re-connects before
the record for the client is created. This race condition is
possible after the nn->client_lock was released. In that case,
the courtesy client is either set to DESTROY_COURTESY or the client
already transited to active (CLIENT_COURTESY is cleared). We check
for this condition and skip calling nfsd4_client_record_remove.
I'll add a comment to note this race condition.

>
> A more explanatory name for @cslist would help readers, IMO.
>
> But maybe this code can be reorganized so that the high-level
> decisions are made clear and the technical details are
> shuffled off into helper functions. I don't have any specific
> suggestions at this point, but I'm going to continue thinking
> about how to make the laundromat a little less cluttered,
> possibly as follow-on work.

If we can defer any work to later phase that would be great!

>
>
>> +}
>> +
>> static time64_t
>> nfs4_laundromat(struct nfsd_net *nn)
>> {
>> @@ -5630,16 +5986,7 @@ nfs4_laundromat(struct nfsd_net *nn)
>> 	}
>> 	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);
> There's already an "INIT_LIST_HEAD(&reaplist);" right above
> this hunk that is repeated inside nfs4_get_client_reaplist().
> Either one (but not both) can be removed.

fix in v14.

>
>
>> 	list_for_each_safe(pos, next, &reaplist) {
>> 		clp = list_entry(pos, struct nfs4_client, cl_lru);
>> 		trace_nfsd_clid_purged(&clp->cl_clientid);
>> @@ -6021,6 +6368,15 @@ static __be32 find_cpntf_state(struct nfsd_net *nn, stateid_t *st,
>> 	found = lookup_clientid(&cps->cp_p_clid, true, nn);
>> 	if (!found)
>> 		goto out;
>> +	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &found->cl_flags)) {
>> +		spin_lock(&found->cl_cs_lock);
>> +		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &found->cl_flags);
>> +		spin_unlock(&found->cl_cs_lock);
>> +		if (atomic_dec_and_lock(&found->cl_rpc_users,
>> +					&nn->client_lock))
>> +			spin_unlock(&nn->client_lock);
>> +		goto out;
>> +	}
>>
>> 	*stid = find_stateid_by_type(found, &cps->cp_p_stateid,
>> 			NFS4_DELEG_STID|NFS4_OPEN_STID|NFS4_LOCK_STID);
>> @@ -6525,6 +6881,43 @@ nfs4_transform_lock_offset(struct file_lock *lock)
>> 		lock->fl_end = OFFSET_MAX;
>> }
>>
>> +/**
>> + * nfsd4_fl_lock_expired - check if lock conflict can be resolved.
>> + *
>> + * @fl: pointer to file_lock with a potential conflict
>> + * Return values:
>> + *   %false: real conflict, lock conflict can not be resolved.
>> + *   %true: no conflict, lock conflict was resolved.
>> + *
>> + * Note that this function is called while the flc_lock is held.
>> + */
>> +static bool
>> +nfsd4_fl_lock_expired(struct file_lock *fl)
> I'd prefer this guy to be named like the newer lm_ functions,
> not the old fl_ functions. So: nfsd4_lm_lock_expired()

This is a bit messy:

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_lock_expired = nfsd4_fl_lock_expired,
};

Most NFS callbacks are named nfsd4_fl_xx and one as
nfsd4_fl_lock_expired. I will change nfsd4_fl_lock_expired to
nfsd4_lm_lock_expired as suggested but note this inconsistency
is still there.


>
> As an aside: I harp a lot on names and on patch descriptions.
> Open source code is meant to enable users to make deep changes
> to the software they use. They can't do that if the code is
> obscure or poorly documented. Thus I view naming and
> descriptions as nearly as critical as proper code licensing
> for open source projects.
>
> But also my memory is failing. The source code has to be
> easily legible a year down the road when I have no
> recollection of what it does or why. :-)

Totally agreed.

>
>
>> +{
>> +	struct nfs4_lockowner *lo;
>> +	struct nfs4_client *clp;
>> +	bool rc = false;
>> +
>> +	if (!fl)
>> +		return false;
>> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
>> +	clp = lo->lo_owner.so_client;
>> +
>> +	/* need to sync with courtesy client trying to reconnect */
>> +	spin_lock(&clp->cl_cs_lock);
>> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
>> +		rc = true;
>> +	else {
>> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>> +			rc =  true;
>> +		} else
>> +			rc =  false;
> Couldn't you write it this way instead:
>
> 	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags))
> 		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
> 	rc = !!test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>
> This is more a check to see whether I understand what's
> going on rather than a request to change the patch.

I think it works the same. Every time I see a '!!' it gives me
a headache :-)

>
>
>> +	}
>> +	spin_unlock(&clp->cl_cs_lock);
>> +	return rc;
>> +}
>> +
>> static fl_owner_t
>> nfsd4_fl_get_owner(fl_owner_t owner)
>> {
>> @@ -6572,6 +6965,7 @@ 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_lock_expired = nfsd4_fl_lock_expired,
>> };
>>
>> static inline void
>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>> index 3e5008b475ff..920fad00e2e4 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..80e565593d83 100644
>> --- a/fs/nfsd/state.h
>> +++ b/fs/nfsd/state.h
>> @@ -345,6 +345,9 @@ 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_CLIENT_COURTESY		(6)	/* be nice to expired client */
> The comment is a little obtuse. If the client is
> actually expired, then it will be ignored and
> destroyed. Maybe "client is unreachable" ?

I think "client is unreachable" is not precise and kind of
confusing so unless you insists I'd like to keep it this way
or just removing it.

>
>
>> +#define NFSD4_CLIENT_DESTROY_COURTESY	(7)
> Maybe NFSD4_CLIENT_EXPIRE_COURTESY ? Dunno.

Unless you, or other reviewers, insist I'd like to keep it this way.

>
>
>> +#define NFSD4_CLIENT_COURTESY_CLNT	(8)	/* used for lookup clientid/name */
> The name CLIENT_COURTESY_CLNT doesn't make sense to me
> when it appears in context. The comment doesn't clarify
> it either. May I suggest:
>
> #define NFSD4_CLIENT_RENEW_COURTESY	(8)	/* courtesy -> active */

The NFSD4_CLIENT_COURTESY_CLNT flag does not mean this courtesy
client will always transit to active client. The flag is used to
indicate this was a courtesy client and it's up to the caller to
take appropriate action; destroy it or create client record before
using it.

>
> Nit: If I'm reading the header file correctly, these new
> definitions should /precede/ the definition of
> NFSD4_CLIENT_CB_FLAG_MASK.

fix in v14.

>
>
>> 	unsigned long		cl_flags;
>> 	const struct cred	*cl_cb_cred;
>> 	struct rpc_clnt		*cl_cb_client;
>> @@ -385,6 +388,9 @@ 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;
> New fields need to be named cl_yada. "cl_courtesy_expiry"
> maybe? Also, please make this a time64_t field.

fix in v14.

>
> Or, would it be possible instead to compute the expiry based
> on the time of the last state renewal? Then a new field wouldn't
> be necessary. I'm not sure, on balance, whether that would add
> or reduce complexity.

fix in v14, remove cl_courtesy_expiry and use the time of the
last state renewal. Thanks! we get rid the new field.

-Dai

>
>
>> +	spinlock_t		cl_cs_lock;
>> +	struct list_head	cl_cs_list;
>> };
>>
>> /* struct nfs4_client_reset
>> -- 
>> 2.9.5
>>
> --
> Chuck Lever
>
>
>

Chuck Lever III Feb. 16, 2022, 4:15 p.m. UTC | #3

> On Feb 16, 2022, at 4:56 AM, Dai Ngo <[e-mail]> wrote:
> 
> On 2/15/22 9:17 AM, Chuck Lever III wrote:
>> 
>>> On Feb 12, 2022, at 1:12 PM, Dai Ngo <[e-mail]> wrote:
>>> 
>>> @@ -3118,6 +3175,14 @@ static __be32 copy_impl_id(struct nfs4_client *clp,
>>> 	return 0;
>>> }
>>> 
>>> +static void
>>> +nfsd4_discard_courtesy_clnt(struct nfs4_client *clp)
>>> +{
>>> +	spin_lock(&clp->cl_cs_lock);
>>> +	set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>> +	spin_unlock(&clp->cl_cs_lock);
>>> +}
>>> +
>>> __be32
>>> nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>> 		union nfsd4_op_u *u)
>>> @@ -3195,6 +3260,10 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>> 	/* Cases below refer to rfc 5661 section 18.35.4: */
>>> 	spin_lock(&nn->client_lock);
>>> 	conf = find_confirmed_client_by_name(&exid->clname, nn);
>>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>>> +		nfsd4_discard_courtesy_clnt(conf);
>>> +		conf = NULL;
>>> +	}
>>> 	if (conf) {
>>> 		bool creds_match = same_creds(&conf->cl_cred, &rqstp->rq_cred);
>>> 		bool verfs_match = same_verf(&verf, &conf->cl_verifier);
>>> @@ -3462,6 +3531,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
>>> 	spin_lock(&nn->client_lock);
>>> 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
>>> 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
>>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>>> +		nfsd4_discard_courtesy_clnt(conf);
>>> +		conf = NULL;
>>> +	}
>> I'm seeing this bit of logic over and over again. I'm wondering
>> why "set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);" cannot
>> be done in the "find_confirmed_yada" functions? The "find" function
>> can even return NULL in that case, so changing all these call sites
>> should be totally unnecessary (except in a couple of cases where I
>> see there is additional logic at the call site).
> 
> This is because not all consumers of find_client_confirm wants to
> discard the courtesy client. The lookup_clientid needs to return the
> courtesy client to its callers because one of the callers needs to
> transit the courtesy client to an active client.

Since find_confirmed_client() is a small function, I would
create a patch that refactors lookup_client() to pull the
existing find_confirmed_client() into that. Apply that patch
first. Then the big patch can change find_confirmed_client()
to set NFSD4_CLIENT_DESTROY_COURTESY.

What about the other find_confirmed_* functions?


>>> +		 */
>>> +		if (!cour) {
>>> +			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>>> +			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
>>> +					NFSD_COURTESY_CLIENT_TIMEOUT;
>>> +			list_add(&clp->cl_cs_list, &cslist);
>> Can cl_lru (or some other existing list_head field)
>> be used instead of cl_cs_list?
> 
> The cl_lru is used for clients to be expired, the cl_cs_list
> is used for courtesy clients and they are treated differently.

Understood, but cl_lru is not a list. It's a field that is
used to attach an nfs4_client _to_ a list.

You should be able to use cl_lru here if the nfs4_client is
going to be added to either reaplist or cslist but not both.


>> I don't see anywhere that removes clp from cslist when
>> this processing is complete. Seems like you will get
>> list corruption next time the laundromat looks at
>> its list of nfs4_clients.
> 
> We re-initialize the list head before every time the laundromat
> runs so there is no need to remove the entries once we're done.

Re-initializing cslist does not change the membership
of the list that was just constructed, it simply orphans
the list. Next time the code does a list_add(&clp->cl_cs_list)
that list will still be there and the nfs4_client will still
be on it.

The nfs4_client has to be explicitly removed from cslist
before the function completes. Otherwise, cl_cs_list
will link those nfs4_client objects to garbage, and the
next time nfs4_get_client_reaplist() is called, that
list_for_each_entry() will walk off the end of the previous
(now phantom) list that the cl_cs_list is still linked to.

Please ensure that there is a "list_del();" somewhere
before the function exits and cslist vanishes. You could,
for example, replace the list_for_each_entry() with a

    while(!list_empty(&cslist)) {
	list_del(&clp->cl_cs_list /* or cl_lru */ );
	...
    }


>>> +/**
>>> + * nfsd4_fl_lock_expired - check if lock conflict can be resolved.
>>> + *
>>> + * @fl: pointer to file_lock with a potential conflict
>>> + * Return values:
>>> + *   %false: real conflict, lock conflict can not be resolved.
>>> + *   %true: no conflict, lock conflict was resolved.
>>> + *
>>> + * Note that this function is called while the flc_lock is held.
>>> + */
>>> +static bool
>>> +nfsd4_fl_lock_expired(struct file_lock *fl)
>> I'd prefer this guy to be named like the newer lm_ functions,
>> not the old fl_ functions. So: nfsd4_lm_lock_expired()
> 
> This is a bit messy:
> 
> 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_lock_expired = nfsd4_fl_lock_expired,
> };
> 
> Most NFS callbacks are named nfsd4_fl_xx and one as
> nfsd4_fl_lock_expired.

The existing lm_notify callback name is correct as it
stands: nfsd4_lm_notify.


> I will change nfsd4_fl_lock_expired to
> nfsd4_lm_lock_expired as suggested but note this inconsistency
> is still there.

The usual practice is to name the function instances
the same as the method names. aef9583b234a ("NFSD: Get
reference of lockowner when coping file_lock") missed
this -- the middle two should both be nfsd4_lm_yada.

I will add a patch to rename these two before you
rebase for v14.


>>> +{
>>> +	struct nfs4_lockowner *lo;
>>> +	struct nfs4_client *clp;
>>> +	bool rc = false;
>>> +
>>> +	if (!fl)
>>> +		return false;
>>> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
>>> +	clp = lo->lo_owner.so_client;
>>> +
>>> +	/* need to sync with courtesy client trying to reconnect */
>>> +	spin_lock(&clp->cl_cs_lock);
>>> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
>>> +		rc = true;
>>> +	else {
>>> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>>> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>> +			rc =  true;
>>> +		} else
>>> +			rc =  false;
>> Couldn't you write it this way instead:
>> 
>> 	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags))
>> 		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>> 	rc = !!test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>> 
>> This is more a check to see whether I understand what's
>> going on rather than a request to change the patch.
> 
> I think it works the same. Every time I see a '!!' it gives me
> a headache :-)

Indeed, it takes some getting used to.


>>> +	}
>>> +	spin_unlock(&clp->cl_cs_lock);
>>> +	return rc;
>>> +}
>>> +
>>> static fl_owner_t
>>> nfsd4_fl_get_owner(fl_owner_t owner)
>>> {
>>> @@ -6572,6 +6965,7 @@ 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_lock_expired = nfsd4_fl_lock_expired,
>>> };
>>> 
>>> static inline void
>>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>>> index 3e5008b475ff..920fad00e2e4 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..80e565593d83 100644
>>> --- a/fs/nfsd/state.h
>>> +++ b/fs/nfsd/state.h
>>> @@ -345,6 +345,9 @@ 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_CLIENT_COURTESY		(6)	/* be nice to expired client */
>> The comment is a little obtuse. If the client is
>> actually expired, then it will be ignored and
>> destroyed. Maybe "client is unreachable" ?
> 
> I think "client is unreachable" is not precise and kind of
> confusing so unless you insists I'd like to keep it this way
> or just removing it.

I think we have to be careful with the terminology.

An expired client is one the server is going to destroy,
and courtesy clients are rather going to be spared. The
whole point of this work is that the server is _not_ going
to expire the client's lease. Calling it an expired client
here is contrary to that intention.

Unless you can think of a concise way to state that in the
comment, let's just remove it.


>>> +#define NFSD4_CLIENT_DESTROY_COURTESY	(7)
>> Maybe NFSD4_CLIENT_EXPIRE_COURTESY ? Dunno.
> 
> Unless you, or other reviewers, insist I'd like to keep it this way.

I think NFSD4_CLIENT_EXPIRED, actually, is going to make
the test_bit()s in fs/nfsd/nfs4state.c more easy to
understand. The transition is courtesy -> expired, right?
And as you say below, the mainline logic has to decide what
to do with one of these clients -- it might not immediately
destroy it, but instead might just want to ignore the
nfs4_client (for example, during lock conflict resolution).

Try NFSD4_CLIENT_EXPIRED. If it's awful we can switch back.
"It's only ones and zeroes."


>>> +#define NFSD4_CLIENT_COURTESY_CLNT	(8)	/* used for lookup clientid/name */
>> The name CLIENT_COURTESY_CLNT doesn't make sense to me
>> when it appears in context. The comment doesn't clarify
>> it either. May I suggest:
>> 
>> #define NFSD4_CLIENT_RENEW_COURTESY	(8)	/* courtesy -> active */
> 
> The NFSD4_CLIENT_COURTESY_CLNT flag does not mean this courtesy
> client will always transit to active client. The flag is used to
> indicate this was a courtesy client and it's up to the caller to
> take appropriate action; destroy it or create client record before
> using it.

I get it: The flag names should reflect a state, not a
requested action.

But I still find CLIENT_COURTESY_CLNT to be unhelpfully
obscure. How about NFSD4_CLIENT_RECONNECTED ?


--
Chuck Lever

Dai Ngo Feb. 18, 2022, 6:03 p.m. UTC | #4

On 2/16/22 8:15 AM, Chuck Lever III wrote:
>> On Feb 16, 2022, at 4:56 AM, Dai Ngo <[e-mail]> wrote:
>>
>> On 2/15/22 9:17 AM, Chuck Lever III wrote:
>>>> On Feb 12, 2022, at 1:12 PM, Dai Ngo <[e-mail]> wrote:
>>>>
>>>> @@ -3118,6 +3175,14 @@ static __be32 copy_impl_id(struct nfs4_client *clp,
>>>> 	return 0;
>>>> }
>>>>
>>>> +static void
>>>> +nfsd4_discard_courtesy_clnt(struct nfs4_client *clp)
>>>> +{
>>>> +	spin_lock(&clp->cl_cs_lock);
>>>> +	set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>>> +	spin_unlock(&clp->cl_cs_lock);
>>>> +}
>>>> +
>>>> __be32
>>>> nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>>> 		union nfsd4_op_u *u)
>>>> @@ -3195,6 +3260,10 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>>> 	/* Cases below refer to rfc 5661 section 18.35.4: */
>>>> 	spin_lock(&nn->client_lock);
>>>> 	conf = find_confirmed_client_by_name(&exid->clname, nn);
>>>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>>>> +		nfsd4_discard_courtesy_clnt(conf);
>>>> +		conf = NULL;
>>>> +	}
>>>> 	if (conf) {
>>>> 		bool creds_match = same_creds(&conf->cl_cred, &rqstp->rq_cred);
>>>> 		bool verfs_match = same_verf(&verf, &conf->cl_verifier);
>>>> @@ -3462,6 +3531,10 @@ nfsd4_create_session(struct svc_rqst *rqstp,
>>>> 	spin_lock(&nn->client_lock);
>>>> 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
>>>> 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
>>>> +	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
>>>> +		nfsd4_discard_courtesy_clnt(conf);
>>>> +		conf = NULL;
>>>> +	}
>>> I'm seeing this bit of logic over and over again. I'm wondering
>>> why "set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);" cannot
>>> be done in the "find_confirmed_yada" functions? The "find" function
>>> can even return NULL in that case, so changing all these call sites
>>> should be totally unnecessary (except in a couple of cases where I
>>> see there is additional logic at the call site).
>> This is because not all consumers of find_client_confirm wants to
>> discard the courtesy client. The lookup_clientid needs to return the
>> courtesy client to its callers because one of the callers needs to
>> transit the courtesy client to an active client.
> Since find_confirmed_client() is a small function, I would
> create a patch that refactors lookup_client() to pull the
> existing find_confirmed_client() into that. Apply that patch
> first. Then the big patch can change find_confirmed_client()
> to set NFSD4_CLIENT_DESTROY_COURTESY.

fix in v14.

>
> What about the other find_confirmed_* functions?

same fix as above in v14.

refactor nfsd4_setclientid to call find_clp_in_name_tree directly
instead of find_confirmed_client_by_name. Modify find_confirmed_client_by_name
to detect and destroy courtesy client.

>
>
>>>> +		 */
>>>> +		if (!cour) {
>>>> +			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>>>> +			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
>>>> +					NFSD_COURTESY_CLIENT_TIMEOUT;
>>>> +			list_add(&clp->cl_cs_list, &cslist);
>>> Can cl_lru (or some other existing list_head field)
>>> be used instead of cl_cs_list?
>> The cl_lru is used for clients to be expired, the cl_cs_list
>> is used for courtesy clients and they are treated differently.
> Understood, but cl_lru is not a list. It's a field that is
> used to attach an nfs4_client _to_ a list.

Yes, cl_lru is a list head to hang the entry on a list.

>
> You should be able to use cl_lru here if the nfs4_client is
> going to be added to either reaplist or cslist but not both.
>
We can not use cl_lru because the courtesy client is still
on nn->client_lru.  We do not remove the courtesy client
from the nn->client_lru list.

>>> I don't see anywhere that removes clp from cslist when
>>> this processing is complete. Seems like you will get
>>> list corruption next time the laundromat looks at
>>> its list of nfs4_clients.
>> We re-initialize the list head before every time the laundromat
>> runs so there is no need to remove the entries once we're done.
> Re-initializing cslist does not change the membership
> of the list that was just constructed, it simply orphans
> the list. Next time the code does a list_add(&clp->cl_cs_list)
> that list will still be there and the nfs4_client will still
> be on it.
>
> The nfs4_client has to be explicitly removed from cslist
> before the function completes. Otherwise, cl_cs_list
> will link those nfs4_client objects to garbage, and the
> next time nfs4_get_client_reaplist() is called, that
> list_for_each_entry() will walk off the end of the previous
> (now phantom) list that the cl_cs_list is still linked to.

Chuck, I don't understand this. Once the cslist list head is
initialized, its next and prev pointer point to itself. When
the courtesy client is added to the tail of the cslist, the
next and prev pointer of cl_cs_list of the courtesy client
are not used and are overwritten so there should not be any
problem even if it was on an orphaned list.

>
> Please ensure that there is a "list_del();" somewhere
> before the function exits and cslist vanishes. You could,
> for example, replace the list_for_each_entry() with a
>
>      while(!list_empty(&cslist)) {
> 	list_del(&clp->cl_cs_list /* or cl_lru */ );
> 	...
>      }

I added the list_del as you suggested but I don't think
it's needed, perhaps I'm missing something.

>
>
>>>> +/**
>>>> + * nfsd4_fl_lock_expired - check if lock conflict can be resolved.
>>>> + *
>>>> + * @fl: pointer to file_lock with a potential conflict
>>>> + * Return values:
>>>> + *   %false: real conflict, lock conflict can not be resolved.
>>>> + *   %true: no conflict, lock conflict was resolved.
>>>> + *
>>>> + * Note that this function is called while the flc_lock is held.
>>>> + */
>>>> +static bool
>>>> +nfsd4_fl_lock_expired(struct file_lock *fl)
>>> I'd prefer this guy to be named like the newer lm_ functions,
>>> not the old fl_ functions. So: nfsd4_lm_lock_expired()
>> This is a bit messy:
>>
>> 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_lock_expired = nfsd4_fl_lock_expired,
>> };
>>
>> Most NFS callbacks are named nfsd4_fl_xx and one as
>> nfsd4_fl_lock_expired.
> The existing lm_notify callback name is correct as it
> stands: nfsd4_lm_notify.
>
>
>> I will change nfsd4_fl_lock_expired to
>> nfsd4_lm_lock_expired as suggested but note this inconsistency
>> is still there.
> The usual practice is to name the function instances
> the same as the method names. aef9583b234a ("NFSD: Get
> reference of lockowner when coping file_lock") missed
> this -- the middle two should both be nfsd4_lm_yada.
>
> I will add a patch to rename these two before you
> rebase for v14.

Thank you!

>
>
>>>> +{
>>>> +	struct nfs4_lockowner *lo;
>>>> +	struct nfs4_client *clp;
>>>> +	bool rc = false;
>>>> +
>>>> +	if (!fl)
>>>> +		return false;
>>>> +	lo = (struct nfs4_lockowner *)fl->fl_owner;
>>>> +	clp = lo->lo_owner.so_client;
>>>> +
>>>> +	/* need to sync with courtesy client trying to reconnect */
>>>> +	spin_lock(&clp->cl_cs_lock);
>>>> +	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
>>>> +		rc = true;
>>>> +	else {
>>>> +		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
>>>> +			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>>> +			rc =  true;
>>>> +		} else
>>>> +			rc =  false;
>>> Couldn't you write it this way instead:
>>>
>>> 	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags))
>>> 		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>> 	rc = !!test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
>>>
>>> This is more a check to see whether I understand what's
>>> going on rather than a request to change the patch.
>> I think it works the same. Every time I see a '!!' it gives me
>> a headache :-)
> Indeed, it takes some getting used to.
>
>
>>>> +	}
>>>> +	spin_unlock(&clp->cl_cs_lock);
>>>> +	return rc;
>>>> +}
>>>> +
>>>> static fl_owner_t
>>>> nfsd4_fl_get_owner(fl_owner_t owner)
>>>> {
>>>> @@ -6572,6 +6965,7 @@ 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_lock_expired = nfsd4_fl_lock_expired,
>>>> };
>>>>
>>>> static inline void
>>>> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
>>>> index 3e5008b475ff..920fad00e2e4 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..80e565593d83 100644
>>>> --- a/fs/nfsd/state.h
>>>> +++ b/fs/nfsd/state.h
>>>> @@ -345,6 +345,9 @@ 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_CLIENT_COURTESY		(6)	/* be nice to expired client */
>>> The comment is a little obtuse. If the client is
>>> actually expired, then it will be ignored and
>>> destroyed. Maybe "client is unreachable" ?
>> I think "client is unreachable" is not precise and kind of
>> confusing so unless you insists I'd like to keep it this way
>> or just removing it.
> I think we have to be careful with the terminology.
>
> An expired client is one the server is going to destroy,
> and courtesy clients are rather going to be spared. The
> whole point of this work is that the server is _not_ going
> to expire the client's lease. Calling it an expired client
> here is contrary to that intention.
>
> Unless you can think of a concise way to state that in the
> comment, let's just remove it.

remove in v14.

>
>
>>>> +#define NFSD4_CLIENT_DESTROY_COURTESY	(7)
>>> Maybe NFSD4_CLIENT_EXPIRE_COURTESY ? Dunno.
>> Unless you, or other reviewers, insist I'd like to keep it this way.
> I think NFSD4_CLIENT_EXPIRED, actually, is going to make
> the test_bit()s in fs/nfsd/nfs4state.c more easy to
> understand. The transition is courtesy -> expired, right?
> And as you say below, the mainline logic has to decide what
> to do with one of these clients -- it might not immediately
> destroy it, but instead might just want to ignore the
> nfs4_client (for example, during lock conflict resolution).
>
> Try NFSD4_CLIENT_EXPIRED
> . If it's awful we can switch back.
> "It's only ones and zeroes."

fix in v14, replace NFSD4_CLIENT_DESTROY_COURTESY with
NFSD4_CLIENT_EXPIRED.

>
>
>>>> +#define NFSD4_CLIENT_COURTESY_CLNT	(8)	/* used for lookup clientid/name */
>>> The name CLIENT_COURTESY_CLNT doesn't make sense to me
>>> when it appears in context. The comment doesn't clarify
>>> it either. May I suggest:
>>>
>>> #define NFSD4_CLIENT_RENEW_COURTESY	(8)	/* courtesy -> active */
>> The NFSD4_CLIENT_COURTESY_CLNT flag does not mean this courtesy
>> client will always transit to active client. The flag is used to
>> indicate this was a courtesy client and it's up to the caller to
>> take appropriate action; destroy it or create client record before
>> using it.
> I get it: The flag names should reflect a state, not a
> requested action.
>
> But I still find CLIENT_COURTESY_CLNT to be unhelpfully
> obscure. How about NFSD4_CLIENT_RECONNECTED ?

fix in v14, replace NFSD4_CLIENT_COURTESY_CLNT with
NFSD4_CLIENT_RECONNECTED.

-Dai

>
>
> --
> Chuck Lever
>
>
>

Chuck Lever III Feb. 18, 2022, 6:28 p.m. UTC | #5

> On Feb 18, 2022, at 1:03 PM, Dai Ngo <[e-mail]> wrote:
> 
> 
> On 2/16/22 8:15 AM, Chuck Lever III wrote:
>>> On Feb 16, 2022, at 4:56 AM, Dai Ngo <[e-mail]> wrote:
>>> 
>>> On 2/15/22 9:17 AM, Chuck Lever III wrote:
>>>>> +		 */
>>>>> +		if (!cour) {
>>>>> +			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
>>>>> +			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
>>>>> +					NFSD_COURTESY_CLIENT_TIMEOUT;
>>>>> +			list_add(&clp->cl_cs_list, &cslist);
>>>> Can cl_lru (or some other existing list_head field)
>>>> be used instead of cl_cs_list?
>>> The cl_lru is used for clients to be expired, the cl_cs_list
>>> is used for courtesy clients and they are treated differently.
>> Understood, but cl_lru is not a list. It's a field that is
>> used to attach an nfs4_client _to_ a list.
> 
> Yes, cl_lru is a list head to hang the entry on a list.
> 
>> 
>> You should be able to use cl_lru here if the nfs4_client is
>> going to be added to either reaplist or cslist but not both.
>> 
> We can not use cl_lru because the courtesy client is still
> on nn->client_lru.  We do not remove the courtesy client
> from the nn->client_lru list.

Thanks, that's what I was missing.


>>>> I don't see anywhere that removes clp from cslist when
>>>> this processing is complete. Seems like you will get
>>>> list corruption next time the laundromat looks at
>>>> its list of nfs4_clients.
>>> We re-initialize the list head before every time the laundromat
>>> runs so there is no need to remove the entries once we're done.
>> Re-initializing cslist does not change the membership
>> of the list that was just constructed, it simply orphans
>> the list. Next time the code does a list_add(&clp->cl_cs_list)
>> that list will still be there and the nfs4_client will still
>> be on it.
>> 
>> The nfs4_client has to be explicitly removed from cslist
>> before the function completes. Otherwise, cl_cs_list
>> will link those nfs4_client objects to garbage, and the
>> next time nfs4_get_client_reaplist() is called, that
>> list_for_each_entry() will walk off the end of the previous
>> (now phantom) list that the cl_cs_list is still linked to.
> 
> Chuck, I don't understand this. Once the cslist list head is
> initialized, its next and prev pointer point to itself. When
> the courtesy client is added to the tail of the cslist, the
> next and prev pointer of cl_cs_list of the courtesy client
> are not used and are overwritten so there should not be any
> problem even if it was on an orphaned list.

When nfs4_get_client_reaplist() returns, what is cl_cs_list
pointing to? At that point IIUC it is linked onto a list
of other nfs4_clients (via their cl_cs_list fields) but
the anchor (cslist) is now in memory that has been returned
to the stack. That's either a problem now, or it's some
technical debt that will bite us later.

Say the NFS client is having network problems. So it might
transition from active to courtesy and back multiple times.

list_add() does not simply initialize the .next and .prev
pointers, it actually dereferences them. The next time this
nfs4_client appears in the laundromat, the list_add will use
the existing values of cl_cs_list.next and cl_cs_list.prev
to link it into the list that cl_cs_list was in during 
previous laundromat pass.


>> Please ensure that there is a "list_del();" somewhere
>> before the function exits and cslist vanishes. You could,
>> for example, replace the list_for_each_entry() with a
>> 
>>     while(!list_empty(&cslist)) {
>> 	list_del(&clp->cl_cs_list /* or cl_lru */ );
>> 	...
>>     }
> 
> I added the list_del as you suggested but I don't think
> it's needed, perhaps I'm missing something.

We might even want list_del_init() here to ensure that
the state of cl_cs_list is correct the next time it is
used in a subsequent call to nfs4_get_client_reaplist.

--
Chuck Lever

Patch

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 32063733443d..b837ff97e097 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1935,10 +1935,33 @@  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) {
+		clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+		/* need to sync with thread resolving lock/deleg conflict */
+		spin_lock(&clp->cl_cs_lock);
+		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
+			spin_unlock(&clp->cl_cs_lock);
+			session = NULL;
+			goto out;
+		}
+		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
+			/*
+			 * clear CLIENT_COURTESY flag to prevent it from being
+			 * destroyed by thread trying to resolve conflicts.
+			 */
+			clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+
+			/* let caller knows it's courtesy client */
+			set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+		}
+		spin_unlock(&clp->cl_cs_lock);
+	}
 	status = nfsd4_get_session_locked(session);
 	if (status)
 		session = NULL;
@@ -2008,6 +2031,7 @@  static struct nfs4_client *alloc_client(struct xdr_netobj name)
 	INIT_LIST_HEAD(&clp->cl_openowners);
 	INIT_LIST_HEAD(&clp->cl_delegations);
 	INIT_LIST_HEAD(&clp->cl_lru);
+	INIT_LIST_HEAD(&clp->cl_cs_list);
 	INIT_LIST_HEAD(&clp->cl_revoked);
 #ifdef CONFIG_NFSD_PNFS
 	INIT_LIST_HEAD(&clp->cl_lo_states);
@@ -2015,6 +2039,7 @@  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:
@@ -2412,6 +2437,10 @@  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_CLIENT_COURTESY, &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);
@@ -2832,8 +2861,22 @@  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
+		else {
+			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+			/* sync with thread resolving lock/deleg conflict */
+			spin_lock(&clp->cl_cs_lock);
+			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
+					&clp->cl_flags)) {
+				spin_unlock(&clp->cl_cs_lock);
+				return NULL;
+			}
+			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
+				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+			}
+			spin_unlock(&clp->cl_cs_lock);
 			return clp;
+		}
 	}
 	return NULL;
 }
@@ -2879,6 +2922,20 @@  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;
+
+			/* need to sync with thread resolving lock/deleg conflict */
+			clear_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+			spin_lock(&clp->cl_cs_lock);
+			if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY,
+					&clp->cl_flags)) {
+				spin_unlock(&clp->cl_cs_lock);
+				continue;
+			}
+			if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
+				clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+				set_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags);
+			}
+			spin_unlock(&clp->cl_cs_lock);
 			renew_client_locked(clp);
 			return clp;
 		}
@@ -3118,6 +3175,14 @@  static __be32 copy_impl_id(struct nfs4_client *clp,
 	return 0;
 }
 
+static void
+nfsd4_discard_courtesy_clnt(struct nfs4_client *clp)
+{
+	spin_lock(&clp->cl_cs_lock);
+	set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
+	spin_unlock(&clp->cl_cs_lock);
+}
+
 __be32
 nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		union nfsd4_op_u *u)
@@ -3195,6 +3260,10 @@  nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	/* Cases below refer to rfc 5661 section 18.35.4: */
 	spin_lock(&nn->client_lock);
 	conf = find_confirmed_client_by_name(&exid->clname, nn);
+	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
+		nfsd4_discard_courtesy_clnt(conf);
+		conf = NULL;
+	}
 	if (conf) {
 		bool creds_match = same_creds(&conf->cl_cred, &rqstp->rq_cred);
 		bool verfs_match = same_verf(&verf, &conf->cl_verifier);
@@ -3462,6 +3531,10 @@  nfsd4_create_session(struct svc_rqst *rqstp,
 	spin_lock(&nn->client_lock);
 	unconf = find_unconfirmed_client(&cr_ses->clientid, true, nn);
 	conf = find_confirmed_client(&cr_ses->clientid, true, nn);
+	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
+		nfsd4_discard_courtesy_clnt(conf);
+		conf = NULL;
+	}
 	WARN_ON_ONCE(conf && unconf);
 
 	if (conf) {
@@ -3493,6 +3566,10 @@  nfsd4_create_session(struct svc_rqst *rqstp,
 			goto out_free_conn;
 		}
 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
+		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &old->cl_flags)) {
+			nfsd4_discard_courtesy_clnt(old);
+			old = NULL;
+		}
 		if (old) {
 			status = mark_client_expired_locked(old);
 			if (status) {
@@ -3631,6 +3708,7 @@  __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
 	struct nfsd4_session *session;
 	struct net *net = SVC_NET(rqstp);
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct nfs4_client *clp;
 
 	if (!nfsd4_last_compound_op(rqstp))
 		return nfserr_not_only_op;
@@ -3663,6 +3741,13 @@  __be32 nfsd4_bind_conn_to_session(struct svc_rqst *rqstp,
 	nfsd4_init_conn(rqstp, conn, session);
 	status = nfs_ok;
 out:
+	clp = session->se_client;
+	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
+		if (status == nfs_ok)
+			nfsd4_client_record_create(clp);
+		else
+			nfsd4_discard_courtesy_clnt(clp);
+	}
 	nfsd4_put_session(session);
 out_no_session:
 	return status;
@@ -3685,6 +3770,7 @@  nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
 	int ref_held_by_me = 0;
 	struct net *net = SVC_NET(r);
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	struct nfs4_client *clp;
 
 	status = nfserr_not_only_op;
 	if (nfsd4_compound_in_session(cstate, sessionid)) {
@@ -3697,6 +3783,13 @@  nfsd4_destroy_session(struct svc_rqst *r, struct nfsd4_compound_state *cstate,
 	ses = find_in_sessionid_hashtbl(sessionid, net, &status);
 	if (!ses)
 		goto out_client_lock;
+	clp = ses->se_client;
+	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
+		status = nfserr_badsession;
+		nfsd4_discard_courtesy_clnt(clp);
+		goto out_put_session;
+	}
+
 	status = nfserr_wrong_cred;
 	if (!nfsd4_mach_creds_match(ses->se_client, r))
 		goto out_put_session;
@@ -3801,7 +3894,7 @@  nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	struct nfsd4_compoundres *resp = rqstp->rq_resp;
 	struct xdr_stream *xdr = resp->xdr;
 	struct nfsd4_session *session;
-	struct nfs4_client *clp;
+	struct nfs4_client *clp = NULL;
 	struct nfsd4_slot *slot;
 	struct nfsd4_conn *conn;
 	__be32 status;
@@ -3911,6 +4004,12 @@  nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (conn)
 		free_conn(conn);
 	spin_unlock(&nn->client_lock);
+	if (clp && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &clp->cl_flags)) {
+		if (status == nfs_ok)
+			nfsd4_client_record_create(clp);
+		else
+			nfsd4_discard_courtesy_clnt(clp);
+	}
 	return status;
 out_put_session:
 	nfsd4_put_session_locked(session);
@@ -3947,6 +4046,10 @@  nfsd4_destroy_clientid(struct svc_rqst *rqstp,
 	spin_lock(&nn->client_lock);
 	unconf = find_unconfirmed_client(&dc->clientid, true, nn);
 	conf = find_confirmed_client(&dc->clientid, true, nn);
+	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
+		nfsd4_discard_courtesy_clnt(conf);
+		conf = NULL;
+	}
 	WARN_ON_ONCE(conf && unconf);
 
 	if (conf) {
@@ -4030,12 +4133,17 @@  nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	struct nfs4_client	*unconf = NULL;
 	__be32 			status;
 	struct nfsd_net		*nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+	struct nfs4_client *cclient = NULL;
 
 	new = create_client(clname, rqstp, &clverifier);
 	if (new == NULL)
 		return nfserr_jukebox;
 	spin_lock(&nn->client_lock);
 	conf = find_confirmed_client_by_name(&clname, nn);
+	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
+		cclient = conf;
+		conf = NULL;
+	}
 	if (conf && client_has_state(conf)) {
 		status = nfserr_clid_inuse;
 		if (clp_used_exchangeid(conf))
@@ -4066,7 +4174,11 @@  nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	new = NULL;
 	status = nfs_ok;
 out:
+	if (cclient)
+		unhash_client_locked(cclient);
 	spin_unlock(&nn->client_lock);
+	if (cclient)
+		expire_client(cclient);
 	if (new)
 		free_client(new);
 	if (unconf) {
@@ -4096,6 +4208,10 @@  nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 	spin_lock(&nn->client_lock);
 	conf = find_confirmed_client(clid, false, nn);
 	unconf = find_unconfirmed_client(clid, false, nn);
+	if (conf && test_bit(NFSD4_CLIENT_COURTESY_CLNT, &conf->cl_flags)) {
+		nfsd4_discard_courtesy_clnt(conf);
+		conf = NULL;
+	}
 	/*
 	 * We try hard to give out unique clientid's, so if we get an
 	 * attempt to confirm the same clientid with a different cred,
@@ -4126,6 +4242,11 @@  nfsd4_setclientid_confirm(struct svc_rqst *rqstp,
 		nfsd4_change_callback(conf, &unconf->cl_cb_conn);
 	} else {
 		old = find_confirmed_client_by_name(&unconf->cl_name, nn);
+		if (old && test_bit(NFSD4_CLIENT_COURTESY_CLNT,
+						&old->cl_flags)) {
+			nfsd4_discard_courtesy_clnt(old);
+			old = NULL;
+		}
 		if (old) {
 			status = nfserr_clid_inuse;
 			if (client_has_state(old)
@@ -4711,18 +4832,41 @@  nfsd_break_deleg_cb(struct file_lock *fl)
 	return ret;
 }
 
+/*
+ * Function returns true if lease conflict was resolved
+ * else returns false.
+ */
 static bool nfsd_breaker_owns_lease(struct file_lock *fl)
 {
 	struct nfs4_delegation *dl = fl->fl_owner;
 	struct svc_rqst *rqst;
 	struct nfs4_client *clp;
 
+	clp = dl->dl_stid.sc_client;
+
+	/*
+	 * need to sync with courtesy client trying to reconnect using
+	 * the cl_cs_lock, nn->client_lock can not be used since this
+	 * function is called with the fl_lck held.
+	 */
+	spin_lock(&clp->cl_cs_lock);
+	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags)) {
+		spin_unlock(&clp->cl_cs_lock);
+		return true;
+	}
+	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
+		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
+		spin_unlock(&clp->cl_cs_lock);
+		return true;
+	}
+	spin_unlock(&clp->cl_cs_lock);
+
 	if (!i_am_nfsd())
-		return NULL;
+		return false;
 	rqst = kthread_data(current);
 	/* Note rq_prog == NFS_ACL_PROGRAM is also possible: */
 	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
-		return NULL;
+		return false;
 	clp = *(rqst->rq_lease_breaker);
 	return dl->dl_stid.sc_client == clp;
 }
@@ -4755,7 +4899,7 @@  static __be32 nfsd4_check_seqid(struct nfsd4_compound_state *cstate, struct nfs4
 }
 
 static struct nfs4_client *lookup_clientid(clientid_t *clid, bool sessions,
-						struct nfsd_net *nn)
+			struct nfsd_net *nn)
 {
 	struct nfs4_client *found;
 
@@ -4785,6 +4929,9 @@  static __be32 set_client(clientid_t *clid,
 	cstate->clp = lookup_clientid(clid, false, nn);
 	if (!cstate->clp)
 		return nfserr_expired;
+
+	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &cstate->clp->cl_flags))
+		nfsd4_client_record_create(cstate->clp);
 	return nfs_ok;
 }
 
@@ -4937,9 +5084,89 @@  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;
+}
+
+/*
+ * 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 false.
+ *	    Check if the deny mode, op_share_deny, would conflict with
+ *	    current access of the file 'fp'.
+ * stp:     skip checking this entry.
+ * new_stp: normal open, not open upgrade.
+ *
+ * Function returns:
+ *	true   - access/deny mode conflict with normal client.
+ *	false  - no conflict or conflict with courtesy client(s) is resolved.
+ */
+static bool
+nfs4_conflict_clients(struct nfs4_file *fp, bool new_stp,
+		struct nfs4_ol_stateid *stp, u32 access, bool share_access)
+{
+	struct nfs4_ol_stateid *st;
+	struct nfs4_client *cl;
+	bool conflict = false;
+
+	lockdep_assert_held(&fp->fi_lock);
+	list_for_each_entry(st, &fp->fi_stateids, st_perfile) {
+		if (st->st_openstp || (st == stp && new_stp) ||
+			(!nfs4_check_access_deny_bmap(st,
+					access, share_access)))
+			continue;
+
+		/* need to sync with courtesy client trying to reconnect */
+		cl = st->st_stid.sc_client;
+		spin_lock(&cl->cl_cs_lock);
+		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags)) {
+			spin_unlock(&cl->cl_cs_lock);
+			continue;
+		}
+		if (test_bit(NFSD4_CLIENT_COURTESY, &cl->cl_flags)) {
+			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &cl->cl_flags);
+			spin_unlock(&cl->cl_cs_lock);
+			continue;
+		}
+		/* conflict not caused by courtesy client */
+		spin_unlock(&cl->cl_cs_lock);
+		conflict = true;
+		break;
+	}
+	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)
+		struct nfsd4_open *open, bool new_stp)
 {
 	struct nfsd_file *nf = NULL;
 	__be32 status;
@@ -4955,15 +5182,29 @@  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);
-		goto out;
+		if (status != nfserr_share_denied) {
+			spin_unlock(&fp->fi_lock);
+			goto out;
+		}
+		if (nfs4_conflict_clients(fp, new_stp, stp,
+				open->op_share_deny, false)) {
+			spin_unlock(&fp->fi_lock);
+			goto out;
+		}
 	}
 
 	/* set access to the file */
 	status = nfs4_file_get_access(fp, open->op_share_access);
 	if (status != nfs_ok) {
-		spin_unlock(&fp->fi_lock);
-		goto out;
+		if (status != nfserr_share_denied) {
+			spin_unlock(&fp->fi_lock);
+			goto out;
+		}
+		if (nfs4_conflict_clients(fp, new_stp, stp,
+				open->op_share_access, true)) {
+			spin_unlock(&fp->fi_lock);
+			goto out;
+		}
 	}
 
 	/* Set access bits in stateid */
@@ -5014,7 +5255,7 @@  nfs4_upgrade_open(struct svc_rqst *rqstp, struct nfs4_file *fp, struct svc_fh *c
 	unsigned char old_deny_bmap = stp->st_deny_bmap;
 
 	if (!test_access(open->op_share_access, stp))
-		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open);
+		return nfs4_get_vfs_file(rqstp, fp, cur_fh, stp, open, false);
 
 	/* test and set deny mode */
 	spin_lock(&fp->fi_lock);
@@ -5363,7 +5604,7 @@  nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
 			goto out;
 		}
 	} else {
-		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
+		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open, true);
 		if (status) {
 			stp->st_stid.sc_type = NFS4_CLOSED_STID;
 			release_open_stateid(stp);
@@ -5597,6 +5838,121 @@  static void nfsd4_ssc_expire_umount(struct nfsd_net *nn)
 }
 #endif
 
+static bool
+nfs4_anylock_blocker(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;
+
+	spin_lock(&clp->cl_lock);
+	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)) {
+						spin_unlock(&clp->cl_lock);
+						return true;
+					}
+				}
+			}
+		}
+	}
+	spin_unlock(&clp->cl_lock);
+	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;
+	struct list_head cslist;
+
+	INIT_LIST_HEAD(reaplist);
+	INIT_LIST_HEAD(&cslist);
+	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;
+
+		/* client expired */
+		if (!client_has_state(clp)) {
+			if (mark_client_expired_locked(clp))
+				continue;
+			list_add(&clp->cl_lru, reaplist);
+			continue;
+		}
+
+		/* expired client has state */
+		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
+			goto exp_client;
+
+		cour = test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+		if (cour &&
+			ktime_get_boottime_seconds() >= clp->courtesy_client_expiry)
+			goto exp_client;
+
+		if (nfs4_anylock_blocker(clp)) {
+			/* expired client has state and has blocker. */
+exp_client:
+			if (mark_client_expired_locked(clp))
+				continue;
+			list_add(&clp->cl_lru, reaplist);
+			continue;
+		}
+		/*
+		 * Client expired and has state and has no blockers.
+		 * If there is race condition with blockers, next time
+		 * the laundromat runs it will catch it and expires
+		 * the client.
+		 */
+		if (!cour) {
+			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+			clp->courtesy_client_expiry = ktime_get_boottime_seconds() +
+					NFSD_COURTESY_CLIENT_TIMEOUT;
+			list_add(&clp->cl_cs_list, &cslist);
+		}
+	}
+	spin_unlock(&nn->client_lock);
+
+	list_for_each_entry(clp, &cslist, cl_cs_list) {
+		spin_lock(&clp->cl_cs_lock);
+		if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags) ||
+			!test_bit(NFSD4_CLIENT_COURTESY,
+					&clp->cl_flags)) {
+			spin_unlock(&clp->cl_cs_lock);
+			continue;
+		}
+		spin_unlock(&clp->cl_cs_lock);
+		nfsd4_client_record_remove(clp);
+	}
+}
+
 static time64_t
 nfs4_laundromat(struct nfsd_net *nn)
 {
@@ -5630,16 +5986,7 @@  nfs4_laundromat(struct nfsd_net *nn)
 	}
 	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);
@@ -6021,6 +6368,15 @@  static __be32 find_cpntf_state(struct nfsd_net *nn, stateid_t *st,
 	found = lookup_clientid(&cps->cp_p_clid, true, nn);
 	if (!found)
 		goto out;
+	if (test_bit(NFSD4_CLIENT_COURTESY_CLNT, &found->cl_flags)) {
+		spin_lock(&found->cl_cs_lock);
+		set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &found->cl_flags);
+		spin_unlock(&found->cl_cs_lock);
+		if (atomic_dec_and_lock(&found->cl_rpc_users,
+					&nn->client_lock))
+			spin_unlock(&nn->client_lock);
+		goto out;
+	}
 
 	*stid = find_stateid_by_type(found, &cps->cp_p_stateid,
 			NFS4_DELEG_STID|NFS4_OPEN_STID|NFS4_LOCK_STID);
@@ -6525,6 +6881,43 @@  nfs4_transform_lock_offset(struct file_lock *lock)
 		lock->fl_end = OFFSET_MAX;
 }
 
+/**
+ * nfsd4_fl_lock_expired - check if lock conflict can be resolved.
+ *
+ * @fl: pointer to file_lock with a potential conflict
+ * Return values:
+ *   %false: real conflict, lock conflict can not be resolved.
+ *   %true: no conflict, lock conflict was resolved.
+ *
+ * Note that this function is called while the flc_lock is held.
+ */
+static bool
+nfsd4_fl_lock_expired(struct file_lock *fl)
+{
+	struct nfs4_lockowner *lo;
+	struct nfs4_client *clp;
+	bool rc = false;
+
+	if (!fl)
+		return false;
+	lo = (struct nfs4_lockowner *)fl->fl_owner;
+	clp = lo->lo_owner.so_client;
+
+	/* need to sync with courtesy client trying to reconnect */
+	spin_lock(&clp->cl_cs_lock);
+	if (test_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags))
+		rc = true;
+	else {
+		if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags)) {
+			set_bit(NFSD4_CLIENT_DESTROY_COURTESY, &clp->cl_flags);
+			rc =  true;
+		} else
+			rc =  false;
+	}
+	spin_unlock(&clp->cl_cs_lock);
+	return rc;
+}
+
 static fl_owner_t
 nfsd4_fl_get_owner(fl_owner_t owner)
 {
@@ -6572,6 +6965,7 @@  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_lock_expired = nfsd4_fl_lock_expired,
 };
 
 static inline void
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 3e5008b475ff..920fad00e2e4 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..80e565593d83 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -345,6 +345,9 @@  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_CLIENT_COURTESY		(6)	/* be nice to expired client */
+#define NFSD4_CLIENT_DESTROY_COURTESY	(7)
+#define NFSD4_CLIENT_COURTESY_CLNT	(8)	/* used for lookup clientid/name */
 	unsigned long		cl_flags;
 	const struct cred	*cl_cb_cred;
 	struct rpc_clnt		*cl_cb_client;
@@ -385,6 +388,9 @@  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;
+	spinlock_t		cl_cs_lock;
+	struct list_head	cl_cs_list;
 };
 
 /* struct nfs4_client_reset