SUNRPC: Ensure the bvecs are reset when we re-encode the RPC request

The bvec tracks the list of pages, so if the number of pages changes
due to a re-encode, we need to reset the bvec as well.

Fixes: 277e4ab ("SUNRPC: Simplify TCP receive code by switching...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.20+

net/sunrpc/clnt.c

@@ -1865,6 +1865,7 @@ rpc_xdr_encode(struct rpc_task *task)
 	req->rq_snd_buf.head[0].iov_len = 0;
 	xdr_init_encode(&xdr, &req->rq_snd_buf,
 			req->rq_snd_buf.head[0].iov_base, req);
+	xdr_free_bvec(&req->rq_snd_buf);
 	if (rpc_encode_header(task, &xdr))
 		return;
 
@@ -1904,8 +1905,6 @@ call_encode(struct rpc_task *task)
 			rpc_call_rpcerror(task, task->tk_status);
 		}
 		return;
-	} else {
-		xprt_request_prepare(task->tk_rqstp);
 	}
 
 	/* Add task to reply queue before transmission to avoid races */

net/sunrpc/xprt.c

@@ -1041,6 +1041,8 @@ xprt_request_enqueue_receive(struct rpc_task *task)
 
 	if (!xprt_request_need_enqueue_receive(task, req))
 		return;
+
+	xprt_request_prepare(task->tk_rqstp);
 	spin_lock(&xprt->queue_lock);
 
 	/* Update the softirq receive buffer */

net/sunrpc/xprtsock.c

@@ -909,6 +909,7 @@ static int xs_nospace(struct rpc_rqst *req)
 static void
 xs_stream_prepare_request(struct rpc_rqst *req)
 {
+	xdr_free_bvec(&req->rq_rcv_buf);
 	req->rq_task->tk_status = xdr_alloc_bvec(&req->rq_rcv_buf, GFP_KERNEL);
 }