NFSv4: add cl_root_cred for use when machine cred is not available.

NFSv4 state management tries a root credential when no machine
credential is available, as can happen with kerberos.
It does this by replacing the cl_machine_cred with a root credential.
This means that any user of the machine credential needs to take
a lock while getting a reference to the machine credential, which is
a little cumbersome.

So introduce an explicit cl_root_cred, and never free either
credential until client shutdown.  This means that no locking
is needed to reference these credentials.  Future patches
will make use of this.

This is only a temporary addition.  both cl_machine_cred and
cl_root_cred will disappear later in the series.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

3 files changed, 15 insertions, 8 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 96d5f8135eb9..cce151776709 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -248,6 +248,8 @@ void nfs_free_client(struct nfs_client *clp)
 
         if (clp->cl_machine_cred != NULL)
                 put_rpccred(clp->cl_machine_cred);
+        if (clp->cl_root_cred != NULL)
+                put_rpccred(clp->cl_root_cred);
 
         put_net(clp->cl_net);
         put_nfs_version(clp->cl_nfs_mod);
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index d8decf2ec48f..511bcdee98f5 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -166,24 +166,28 @@ out:
 
 struct rpc_cred *nfs4_get_machine_cred_locked(struct nfs_client *clp)
 {
-        struct rpc_cred *cred = NULL;
+        struct rpc_cred *cred = clp->cl_root_cred;
 
-        if (clp->cl_machine_cred != NULL)
-                cred = get_rpccred(clp->cl_machine_cred);
+        if (!cred)
+                cred = clp->cl_machine_cred;
+        if (cred)
+                return get_rpccred(cred);
         return cred;
 }
 
 static void nfs4_root_machine_cred(struct nfs_client *clp)
 {
-        struct rpc_cred *cred, *new;
+        struct rpc_cred *new;
 
         new = rpc_lookup_machine_cred(NULL);
         spin_lock(&clp->cl_lock);
-        cred = clp->cl_machine_cred;
-        clp->cl_machine_cred = new;
+        if (clp->cl_root_cred == NULL) {
+                clp->cl_root_cred = new;
+                new = NULL;
+        }
         spin_unlock(&clp->cl_lock);
-        if (cred != NULL)
-                put_rpccred(cred);
+        if (new != NULL)
+                put_rpccred(new);
 }
 
 static struct rpc_cred *
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 0fc0b9135d46..fea51b44fe50 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -59,6 +59,7 @@ struct nfs_client {
 
         u32                     cl_minorversion;/* NFSv4 minorversion */
         struct rpc_cred         *cl_machine_cred;
+        struct rpc_cred         *cl_root_cred;  /* Use when machine_cred is ineffective */
 
 #if IS_ENABLED(CONFIG_NFS_V4)
         struct list_head        cl_ds_clients; /* auth flavor data servers */