SUNRPC: Fix read ordering problems with req->rq_private_buf.len

We want to ensure that req->rq_private_buf.len is updated before
req->rq_received, so that call_decode() doesn't use an old value for
req->rq_rcv_buf.len.

In 'call_decode()' itself, instead of using task->tk_status (which is set
using req->rq_received) must use the actual value of
req->rq_private_buf.len when deciding whether or not the received RPC reply
is too short.

Finally ensure that we set req->rq_rcv_buf.len to zero when retrying a
request. A typo meant that we were resetting req->rq_private_buf.len in
call_decode(), and then clobbering that value with the old rq_rcv_buf.len
again in xprt_transmit().
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/clnt.c

@@ -1199,18 +1199,6 @@ call_decode(struct rpc_task *task)
 		task->tk_flags &= ~RPC_CALL_MAJORSEEN;
 	}
 
-	if (task->tk_status < 12) {
-		if (!RPC_IS_SOFT(task)) {
-			task->tk_action = call_bind;
-			clnt->cl_stats->rpcretrans++;
-			goto out_retry;
-		}
-		dprintk("RPC:       %s: too small RPC reply size (%d bytes)\n",
-				clnt->cl_protname, task->tk_status);
-		task->tk_action = call_timeout;
-		goto out_retry;
-	}
-
 	/*
 	 * Ensure that we see all writes made by xprt_complete_rqst()
 	 * before it changed req->rq_received.
@@ -1222,6 +1210,18 @@ call_decode(struct rpc_task *task)
 	WARN_ON(memcmp(&req->rq_rcv_buf, &req->rq_private_buf,
 				sizeof(req->rq_rcv_buf)) != 0);
 
+	if (req->rq_rcv_buf.len < 12) {
+		if (!RPC_IS_SOFT(task)) {
+			task->tk_action = call_bind;
+			clnt->cl_stats->rpcretrans++;
+			goto out_retry;
+		}
+		dprintk("RPC:       %s: too small RPC reply size (%d bytes)\n",
+				clnt->cl_protname, task->tk_status);
+		task->tk_action = call_timeout;
+		goto out_retry;
+	}
+
 	/* Verify the RPC header */
 	p = call_verify(task);
 	if (IS_ERR(p)) {
@@ -1243,7 +1243,7 @@ call_decode(struct rpc_task *task)
 	task->tk_status = 0;
 	/* Note: call_verify() may have freed the RPC slot */
 	if (task->tk_rqstp == req) {
-		req->rq_received = req->rq_private_buf.len = 0;
+		req->rq_received = req->rq_rcv_buf.len = 0;
 		if (task->tk_client->cl_discrtry)
 			xprt_force_disconnect(task->tk_xprt);
 	}

net/sunrpc/xprt.c

@@ -757,9 +757,10 @@ void xprt_complete_rqst(struct rpc_task *task, int copied)
 	task->tk_rtt = (long)jiffies - req->rq_xtime;
 
 	list_del_init(&req->rq_list);
+	req->rq_private_buf.len = copied;
 	/* Ensure all writes are done before we update req->rq_received */
 	smp_wmb();
-	req->rq_received = req->rq_private_buf.len = copied;
+	req->rq_received = copied;
 	rpc_wake_up_queued_task(&xprt->pending, task);
 }
 EXPORT_SYMBOL_GPL(xprt_complete_rqst);