Re: [PATCH RFC 1/1] nfsd: Initial implementation of NFSv4 Courteous Server

dai.ngo@xxxxxxxxxx · Wed, 16 Jun 2021 12:17:27 -0700

On 6/16/21 9:02 AM, J. Bruce Fields wrote:
On Thu, Jun 03, 2021 at 02:14:38PM -0400, Dai Ngo wrote:
Currently an NFSv4 client must maintain its lease by using the at least
one of the state tokens or if nothing else, by issuing a RENEW (4.0), or
a singleton SEQUENCE (4.1) at least once during each lease period. If the
client fails to renew the lease, for any reason, the Linux server expunges
the state tokens immediately upon detection of the "failure to renew the
lease" condition and begins returning NFS4ERR_EXPIRED if the client should
reconnect and attempt to use the (now) expired state.

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

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

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

. when the laundromat thread detects an expired client and if that client
still has established states on the Linux server then marks the client as a
COURTESY_CLIENT and skips destroying the client and all its states,
otherwise destroy the client as usual.

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

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

To be done:

. fix a problem with 4.1 where the Linux server keeps returning
SEQ4_STATUS_CB_PATH_DOWN in the successful SEQUENCE reply, after the expired
client re-connects, causing the client to keep sending BCTS requests to server.
Hm, any progress working out what's causing that?

I will fix this in v2 patch.


. handle OPEN conflict with share reservations.
Sounds doable.

Yes. But I don't know a way to force the Linux client to specify the
deny mode on OPEN. I may have to test this with SMB client: expired
NFS client should not prevent SMB client from open the file with
deny mode.


. instead of destroy the client anf all its state on conflict, only destroy
the state that is conflicted with the current request.
The other todos I think have to be done before we merge, but this one I
think can wait.

. destroy the COURTESY_CLIENT either after a fixed period of time to release
resources or as reacting to memory pressure.
I think we need something here, but it can be pretty simple.

ok.


Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
---
  fs/nfsd/nfs4state.c        | 94 +++++++++++++++++++++++++++++++++++++++++++---
  fs/nfsd/state.h            |  1 +
  include/linux/sunrpc/svc.h |  1 +
  3 files changed, 91 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index b517a8794400..969995872752 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -171,6 +171,7 @@ renew_client_locked(struct nfs4_client *clp)
  
  	list_move_tail(&clp->cl_lru, &nn->client_lru);
  	clp->cl_time = ktime_get_boottime_seconds();
+	clear_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
  }
  
  static void put_client_renew_locked(struct nfs4_client *clp)
@@ -4610,6 +4611,38 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
  	nfsd4_run_cb(&dp->dl_recall);
  }
  
+/*
+ * Set rq_conflict_client if the conflict client have expired
+ * and return true, otherwise return false.
+ */
+static bool
+nfsd_set_conflict_client(struct nfs4_delegation *dp)
+{
+	struct svc_rqst *rqst;
+	struct nfs4_client *clp;
+	struct nfsd_net *nn;
+	bool ret;
+
+	if (!i_am_nfsd())
+		return false;
+	rqst = kthread_data(current);
+	if (rqst->rq_prog != NFS_PROGRAM || rqst->rq_vers < 4)
+		return false;
This says we do nothing if the lock request is not coming from nfsd and
v4.  That doesn't sound right.

For example, if the conflicting lock is coming from a local process (not
from an NFS client at all), we still need to revoke the courtesy state
so that process can make progress.

The reason it checks for NFS request is because it uses rq_conflict_client
to pass the expired client back to the upper layer which then does the
expire_client. If this is not from a NFS request then kthread_data() might
not be the svc_rqst. In that case the code will try to recall the delegation
from the expired client and the recall will eventually timed out.

I will rework this code.

Thanks,
-Dai

+	rqst->rq_conflict_client = NULL;
+	clp = dp->dl_recall.cb_clp;
+	nn = net_generic(clp->net, nfsd_net_id);
+	spin_lock(&nn->client_lock);
+
+	if (test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags) &&
+				!mark_client_expired_locked(clp)) {
+		rqst->rq_conflict_client = clp;
+		ret = true;
+	} else
+		ret = false;
+	spin_unlock(&nn->client_lock);
+	return ret;
+}
+
  /* Called from break_lease() with i_lock held. */
  static bool
  nfsd_break_deleg_cb(struct file_lock *fl)
@@ -4618,6 +4651,8 @@ nfsd_break_deleg_cb(struct file_lock *fl)
  	struct nfs4_delegation *dp = (struct nfs4_delegation *)fl->fl_owner;
  	struct nfs4_file *fp = dp->dl_stid.sc_file;
  
+	if (nfsd_set_conflict_client(dp))
+		return false;
  	trace_nfsd_deleg_break(&dp->dl_stid.sc_stateid);
  
  	/*
@@ -5237,6 +5272,22 @@ static void nfsd4_deleg_xgrade_none_ext(struct nfsd4_open *open,
  	 */
  }
  
+static bool
+nfs4_destroy_courtesy_client(struct nfs4_client *clp)
+{
+	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
+
+	spin_lock(&nn->client_lock);
+	if (!test_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags) ||
+			mark_client_expired_locked(clp)) {
+		spin_unlock(&nn->client_lock);
+		return false;
+	}
+	spin_unlock(&nn->client_lock);
+	expire_client(clp);
+	return true;
+}
+
  __be32
  nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nfsd4_open *open)
  {
@@ -5286,7 +5337,13 @@ nfsd4_process_open2(struct svc_rqst *rqstp, struct svc_fh *current_fh, struct nf
  			goto out;
  		}
  	} else {
+		rqstp->rq_conflict_client = NULL;
  		status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
+		if (status == nfserr_jukebox && rqstp->rq_conflict_client) {
+			if (nfs4_destroy_courtesy_client(rqstp->rq_conflict_client))
+				status = nfs4_get_vfs_file(rqstp, fp, current_fh, stp, open);
+		}
+
  		if (status) {
  			stp->st_stid.sc_type = NFS4_CLOSED_STID;
  			release_open_stateid(stp);
@@ -5472,6 +5529,8 @@ nfs4_laundromat(struct nfsd_net *nn)
  	};
  	struct nfs4_cpntf_state *cps;
  	copy_stateid_t *cps_t;
+	struct nfs4_stid *stid;
+	int id = 0;
  	int i;
  
  	if (clients_still_reclaiming(nn)) {
@@ -5495,6 +5554,15 @@ nfs4_laundromat(struct nfsd_net *nn)
  		clp = list_entry(pos, struct nfs4_client, cl_lru);
  		if (!state_expired(&lt, clp->cl_time))
  			break;
+
+		spin_lock(&clp->cl_lock);
+		stid = idr_get_next(&clp->cl_stateids, &id);
+		spin_unlock(&clp->cl_lock);
+		if (stid) {
+			/* client still has states */
+			set_bit(NFSD4_CLIENT_COURTESY, &clp->cl_flags);
+			continue;
+		}
  		if (mark_client_expired_locked(clp)) {
  			trace_nfsd_clid_expired(&clp->cl_clientid);
  			continue;
@@ -6440,7 +6508,7 @@ static const struct lock_manager_operations nfsd_posix_mng_ops  = {
  	.lm_put_owner = nfsd4_fl_put_owner,
  };
  
-static inline void
+static inline int
  nfs4_set_lock_denied(struct file_lock *fl, struct nfsd4_lock_denied *deny)
  {
  	struct nfs4_lockowner *lo;
@@ -6453,6 +6521,8 @@ nfs4_set_lock_denied(struct file_lock *fl, struct nfsd4_lock_denied *deny)
  			/* We just don't care that much */
  			goto nevermind;
  		deny->ld_clientid = lo->lo_owner.so_client->cl_clientid;
+		if (nfs4_destroy_courtesy_client(lo->lo_owner.so_client))
+			return -EAGAIN;
  	} else {
  nevermind:
  		deny->ld_owner.len = 0;
@@ -6467,6 +6537,7 @@ nfs4_set_lock_denied(struct file_lock *fl, struct nfsd4_lock_denied *deny)
  	deny->ld_type = NFS4_READ_LT;
  	if (fl->fl_type != F_RDLCK)
  		deny->ld_type = NFS4_WRITE_LT;
+	return 0;
  }
  
  static struct nfs4_lockowner *
@@ -6734,6 +6805,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  	unsigned int fl_flags = FL_POSIX;
  	struct net *net = SVC_NET(rqstp);
  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+	bool retried = false;
  
  	dprintk("NFSD: nfsd4_lock: start=%Ld length=%Ld\n",
  		(long long) lock->lk_offset,
@@ -6860,7 +6932,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  		list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
  		spin_unlock(&nn->blocked_locks_lock);
  	}
-
+again:
  	err = vfs_lock_file(nf->nf_file, F_SETLK, file_lock, conflock);
  	switch (err) {
  	case 0: /* success! */
@@ -6875,7 +6947,12 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  	case -EAGAIN:		/* conflock holds conflicting lock */
  		status = nfserr_denied;
  		dprintk("NFSD: nfsd4_lock: conflicting lock found!\n");
-		nfs4_set_lock_denied(conflock, &lock->lk_denied);
+
+		/* try again if conflict with courtesy client  */
+		if (nfs4_set_lock_denied(conflock, &lock->lk_denied) == -EAGAIN && !retried) {
+			retried = true;
+			goto again;
+		}
  		break;
  	case -EDEADLK:
  		status = nfserr_deadlock;
@@ -6962,6 +7039,8 @@ nfsd4_lockt(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  	struct nfs4_lockowner *lo = NULL;
  	__be32 status;
  	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
+	bool retried = false;
+	int ret;
  
  	if (locks_in_grace(SVC_NET(rqstp)))
  		return nfserr_grace;
@@ -7010,14 +7089,19 @@ nfsd4_lockt(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
  	file_lock->fl_end = last_byte_offset(lockt->lt_offset, lockt->lt_length);
  
  	nfs4_transform_lock_offset(file_lock);
-
+again:
  	status = nfsd_test_lock(rqstp, &cstate->current_fh, file_lock);
  	if (status)
  		goto out;
  
  	if (file_lock->fl_type != F_UNLCK) {
  		status = nfserr_denied;
-		nfs4_set_lock_denied(file_lock, &lockt->lt_denied);
+		ret = nfs4_set_lock_denied(file_lock, &lockt->lt_denied);
+		if (ret == -EAGAIN && !retried) {
+			retried = true;
+			fh_clear_wcc(&cstate->current_fh);
+			goto again;
+		}
  	}
  out:
  	if (lo)
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e73bdbb1634a..bdc3605e3722 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -345,6 +345,7 @@ 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 */
  	unsigned long		cl_flags;
  	const struct cred	*cl_cb_cred;
  	struct rpc_clnt		*cl_cb_client;
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index e91d51ea028b..2f0382f9d0ff 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -304,6 +304,7 @@ struct svc_rqst {
  						 * net namespace
  						 */
  	void **			rq_lease_breaker; /* The v4 client breaking a lease */
+	void			*rq_conflict_client;
  };
  
  #define SVC_NET(rqst) (rqst->rq_xprt ? rqst->rq_xprt->xpt_net : rqst->rq_bc_net)
--
2.9.5






