[PATCH 2/6] nfsd: return hard failure for OP_SETCLIENTID when there are too many clients.

[NeilBrown <neilb@suse.de>]

If there are more non-courteous clients than the calculated limit, we
should fail the request rather than report a soft failure and
encouraging the client to retry indefinitely.

The only hard failure allowed for EXCHANGE_ID that doesn't clearly have
some other meaning is NFS4ERR_SERVERFAULT.  So use that, but explain why
in a comment at each place that it is returned.

If there are courteous clients which push us over the limit, then expedite
their removal.

This is not known to have caused a problem is production use, but
testing of lots of clients reports repeated NFS4ERR_DELAY responses
which doesn't seem helpful.

Also remove an outdated comment - we do use a slab cache.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/nfsd/nfs4state.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 56b261608af4..ca6b5b52f77d 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2212,21 +2212,20 @@ STALE_CLIENTID(clientid_t *clid, struct nfsd_net *nn)
 	return 1;
 }
 
-/* 
- * XXX Should we use a slab cache ?
- * This type of memory management is somewhat inefficient, but we use it
- * anyway since SETCLIENTID is not a common operation.
- */
 static struct nfs4_client *alloc_client(struct xdr_netobj name,
 				struct nfsd_net *nn)
 {
 	struct nfs4_client *clp;
 	int i;
 
-	if (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients) {
+	if (atomic_read(&nn->nfs4_client_count) -
+	    atomic_read(&nn->nfsd_courtesy_clients) >= nn->nfs4_max_clients)
+		return ERR_PTR(-EUSERS);
+
+	if (atomic_read(&nn->nfs4_client_count) >= nn->nfs4_max_clients &&
+	    atomic_read(&nn->nfsd_courtesy_clients) > 0)
 		mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);
-		return NULL;
-	}
+
 	clp = kmem_cache_zalloc(client_slab, GFP_KERNEL);
 	if (clp == NULL)
 		return NULL;
@@ -3121,8 +3120,8 @@ static struct nfs4_client *create_client(struct xdr_netobj name,
 	struct dentry *dentries[ARRAY_SIZE(client_files)];
 
 	clp = alloc_client(name, nn);
-	if (clp == NULL)
-		return NULL;
+	if (IS_ERR_OR_NULL(clp))
+		return clp;
 
 	ret = copy_cred(&clp->cl_cred, &rqstp->rq_cred);
 	if (ret) {
@@ -3504,6 +3503,11 @@ nfsd4_exchange_id(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	new = create_client(exid->clname, rqstp, &verf);
 	if (new == NULL)
 		return nfserr_jukebox;
+	if (IS_ERR(new))
+		/* Protocol has no specific error for "client limit reached".
+		 * NFS4ERR_RESOURCE is not permitted for EXCHANGE_ID
+		 */
+		return nfserr_serverfault;
 	status = copy_impl_id(new, exid);
 	if (status)
 		goto out_nolock;
@@ -4422,6 +4426,12 @@ nfsd4_setclientid(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	new = create_client(clname, rqstp, &clverifier);
 	if (new == NULL)
 		return nfserr_jukebox;
+	if (IS_ERR(new))
+		/* Protocol has no specific error for "client limit reached".
+		 * NFS4ERR_RESOURCE, while allowed for SETCLIENTID, implies
+		 * that a smaller COMPOUND might be successful.
+		 */
+		return nfserr_serverfault;
 	spin_lock(&nn->client_lock);
 	conf = find_confirmed_client_by_name(&clname, nn);
 	if (conf && client_has_state(conf)) {
-- 
2.46.0