SUNRPC: handle malloc failure in ->request_prepare

If ->request_prepare() detects an error, it sets ->rq_task->tk_status.
This is easy for callers to ignore.
The only caller is xprt_request_enqueue_receive() and it does ignore the
error, as does call_encode() which calls it.  This can result in a
request being queued to receive a reply without an allocated receive buffer.

So instead of setting rq_task->tk_status, return an error, and store in
->tk_status only in call_encode();

The call to xprt_request_enqueue_receive() is now earlier in
call_encode(), where the error can still be handled.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

include/linux/sunrpc/xprt.h

@@ -144,7 +144,7 @@ struct rpc_xprt_ops {
 	unsigned short	(*get_srcport)(struct rpc_xprt *xprt);
 	int		(*buf_alloc)(struct rpc_task *task);
 	void		(*buf_free)(struct rpc_task *task);
-	void		(*prepare_request)(struct rpc_rqst *req);
+	int		(*prepare_request)(struct rpc_rqst *req);
 	int		(*send_request)(struct rpc_rqst *req);
 	void		(*wait_for_reply_request)(struct rpc_task *task);
 	void		(*timer)(struct rpc_xprt *xprt, struct rpc_task *task);
@@ -357,10 +357,9 @@ int			xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task);
 void			xprt_free_slot(struct rpc_xprt *xprt,
 				       struct rpc_rqst *req);
-void			xprt_request_prepare(struct rpc_rqst *req);
 bool			xprt_prepare_transmit(struct rpc_task *task);
 void			xprt_request_enqueue_transmit(struct rpc_task *task);
-void			xprt_request_enqueue_receive(struct rpc_task *task);
+int			xprt_request_enqueue_receive(struct rpc_task *task);
 void			xprt_request_wait_receive(struct rpc_task *task);
 void			xprt_request_dequeue_xprt(struct rpc_task *task);
 bool			xprt_request_need_retransmit(struct rpc_task *task);

net/sunrpc/clnt.c

@@ -1858,6 +1858,9 @@ call_encode(struct rpc_task *task)
 	xprt_request_dequeue_xprt(task);
 	/* Encode here so that rpcsec_gss can use correct sequence number. */
 	rpc_xdr_encode(task);
+	/* Add task to reply queue before transmission to avoid races */
+	if (task->tk_status == 0 && rpc_reply_expected(task))
+		task->tk_status = xprt_request_enqueue_receive(task);
 	/* Did the encode result in an error condition? */
 	if (task->tk_status != 0) {
 		/* Was the error nonfatal? */
@@ -1881,9 +1884,6 @@ call_encode(struct rpc_task *task)
 		return;
 	}
 
-	/* Add task to reply queue before transmission to avoid races */
-	if (rpc_reply_expected(task))
-		xprt_request_enqueue_receive(task);
 	xprt_request_enqueue_transmit(task);
 out:
 	task->tk_action = call_transmit;

net/sunrpc/xprt.c

@@ -69,10 +69,11 @@
 /*
  * Local functions
  */
-static void	 xprt_init(struct rpc_xprt *xprt, struct net *net);
+static void	xprt_init(struct rpc_xprt *xprt, struct net *net);
 static __be32	xprt_alloc_xid(struct rpc_xprt *xprt);
-static void	 xprt_destroy(struct rpc_xprt *xprt);
-static void	 xprt_request_init(struct rpc_task *task);
+static void	xprt_destroy(struct rpc_xprt *xprt);
+static void	xprt_request_init(struct rpc_task *task);
+static int	xprt_request_prepare(struct rpc_rqst *req);
 
 static DEFINE_SPINLOCK(xprt_list_lock);
 static LIST_HEAD(xprt_list);
@@ -1143,16 +1144,19 @@ xprt_request_need_enqueue_receive(struct rpc_task *task, struct rpc_rqst *req)
  * @task: RPC task
  *
  */
-void
+int
 xprt_request_enqueue_receive(struct rpc_task *task)
 {
 	struct rpc_rqst *req = task->tk_rqstp;
 	struct rpc_xprt *xprt = req->rq_xprt;
+	int ret;
 
 	if (!xprt_request_need_enqueue_receive(task, req))
-		return;
+		return 0;
 
-	xprt_request_prepare(task->tk_rqstp);
+	ret = xprt_request_prepare(task->tk_rqstp);
+	if (ret)
+		return ret;
 	spin_lock(&xprt->queue_lock);
 
 	/* Update the softirq receive buffer */
@@ -1166,6 +1170,7 @@ xprt_request_enqueue_receive(struct rpc_task *task)
 
 	/* Turn off autodisconnect */
 	del_singleshot_timer_sync(&xprt->timer);
+	return 0;
 }
 
 /**
@@ -1452,14 +1457,16 @@ xprt_request_dequeue_xprt(struct rpc_task *task)
  *
  * Calls into the transport layer to do whatever is needed to prepare
  * the request for transmission or receive.
+ * Returns error, or zero.
  */
-void
+static int
 xprt_request_prepare(struct rpc_rqst *req)
 {
 	struct rpc_xprt *xprt = req->rq_xprt;
 
 	if (xprt->ops->prepare_request)
-		xprt->ops->prepare_request(req);
+		return xprt->ops->prepare_request(req);
+	return 0;
 }
 
 /**

net/sunrpc/xprtsock.c

@@ -822,11 +822,11 @@ static int xs_stream_nospace(struct rpc_rqst *req, bool vm_wait)
 	return ret;
 }
 
-static void
+static int
 xs_stream_prepare_request(struct rpc_rqst *req)
 {
 	xdr_free_bvec(&req->rq_rcv_buf);
-	req->rq_task->tk_status = xdr_alloc_bvec(
+	return xdr_alloc_bvec(
 		&req->rq_rcv_buf, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);
 }