NFS: Return error code from nfs_callback_up() to user space

If the kernel cannot start the NFSv4 callback service during a mount
request, it returns -ENOMEM to user space, resulting in this message:

   mount.nfs4: Cannot allocate memory

Adjust nfs_alloc_client() and nfs_get_client() to pass NFSv4 callback
start-up errors back to user space so a less mysterious error message
can be displayed by the mount command.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/client.c

@@ -114,6 +114,7 @@ static struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_
 {
 	struct nfs_client *clp;
 	struct rpc_cred *cred;
+	int err = -ENOMEM;
 
 	if ((clp = kzalloc(sizeof(*clp), GFP_KERNEL)) == NULL)
 		goto error_0;
@@ -121,7 +122,8 @@ static struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_
 	clp->rpc_ops = cl_init->rpc_ops;
 
 	if (cl_init->rpc_ops->version == 4) {
-		if (nfs_callback_up() < 0)
+		err = nfs_callback_up();
+		if (err < 0)
 			goto error_2;
 		__set_bit(NFS_CS_CALLBACK, &clp->cl_res_state);
 	}
@@ -133,6 +135,7 @@ static struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_
 	clp->cl_addrlen = cl_init->addrlen;
 
 	if (cl_init->hostname) {
+		err = -ENOMEM;
 		clp->cl_hostname = kstrdup(cl_init->hostname, GFP_KERNEL);
 		if (!clp->cl_hostname)
 			goto error_3;
@@ -165,7 +168,7 @@ error_3:
 error_2:
 	kfree(clp);
 error_0:
-	return NULL;
+	return ERR_PTR(err);
 }
 
 static void nfs4_shutdown_client(struct nfs_client *clp)
@@ -456,9 +459,10 @@ static struct nfs_client *nfs_get_client(const struct nfs_client_initdata *cl_in
 		spin_unlock(&nfs_client_lock);
 
 		new = nfs_alloc_client(cl_init);
-	} while (new);
+	} while (!IS_ERR(new));
 
-	return ERR_PTR(-ENOMEM);
+	dprintk("--> nfs_get_client() = %ld [failed]\n", PTR_ERR(new));
+	return new;
 
 	/* install a new client and return with it unready */
 install_client: