nfs41: renewd sequence operations should take/put client reference

renewd sends SEQUENCE requests to the NFS server in order to renew state.
As the request is asynchronous, renewd should take a reference to the
nfs_client to prevent concurrent umounts from freeing the session/client
Signed-off-by: NAlexandros Batsakis <batsakis@netapp.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4proc.c

@@ -419,7 +419,8 @@ static void nfs41_sequence_done(struct nfs_client *clp,
 			clp->cl_last_renewal = timestamp;
 		spin_unlock(&clp->cl_lock);
 		/* Check sequence flags */
-		nfs41_handle_sequence_flag_errors(clp, res->sr_status_flags);
+		if (atomic_read(&clp->cl_count) > 1)
+			nfs41_handle_sequence_flag_errors(clp, res->sr_status_flags);
 	}
 out:
 	/* The session may be reset by one of the error handlers. */
@@ -5035,7 +5036,9 @@ static void nfs41_sequence_release(void *data)
 {
 	struct nfs_client *clp = (struct nfs_client *)data;
 
-	nfs4_schedule_state_renewal(clp);
+	if (atomic_read(&clp->cl_count) > 1)
+		nfs4_schedule_state_renewal(clp);
+	nfs_put_client(clp);
 }
 
 static void nfs41_sequence_call_done(struct rpc_task *task, void *data)
@@ -5046,6 +5049,8 @@ static void nfs41_sequence_call_done(struct rpc_task *task, void *data)
 
 	if (task->tk_status < 0) {
 		dprintk("%s ERROR %d\n", __func__, task->tk_status);
+		if (atomic_read(&clp->cl_count) == 1)
+			goto out;
 
 		if (_nfs4_async_handle_error(task, NULL, clp, NULL)
 								== -EAGAIN) {
@@ -5054,7 +5059,7 @@ static void nfs41_sequence_call_done(struct rpc_task *task, void *data)
 		}
 	}
 	dprintk("%s rpc_cred %p\n", __func__, task->tk_msg.rpc_cred);
-
+out:
 	kfree(task->tk_msg.rpc_argp);
 	kfree(task->tk_msg.rpc_resp);
 
@@ -5092,12 +5097,13 @@ static int nfs41_proc_async_sequence(struct nfs_client *clp,
 		.rpc_cred = cred,
 	};
 
+	if (!atomic_inc_not_zero(&clp->cl_count))
+		return -EIO;
 	args = kzalloc(sizeof(*args), GFP_KERNEL);
-	if (!args)
-		return -ENOMEM;
 	res = kzalloc(sizeof(*res), GFP_KERNEL);
-	if (!res) {
+	if (!args || !res) {
 		kfree(args);
+		nfs_put_client(clp);
 		return -ENOMEM;
 	}
 	res->sr_slotid = NFS4_MAX_SLOT_TABLE;