svcrdma: Fix page leak in svc_rdma_recv_read_chunk()

Commit 07d0ff3b ("svcrdma: Clean up Read chunk path") moved the
page saver logic so that it gets executed event when an error occurs.
In that case, the I/O is never posted, and those pages are then
leaked. Errors in this path, however, are quite rare.

Fixes: 07d0ff3b ("svcrdma: Clean up Read chunk path")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

net/sunrpc/xprtrdma/svc_rdma_rw.c

@@ -684,7 +684,6 @@ static int svc_rdma_build_read_chunk(struct svc_rqst *rqstp,
 				     struct svc_rdma_read_info *info,
 				     __be32 *p)
 {
-	unsigned int i;
 	int ret;
 
 	ret = -EINVAL;
@@ -707,12 +706,6 @@ static int svc_rdma_build_read_chunk(struct svc_rqst *rqstp,
 		info->ri_chunklen += rs_length;
 	}
 
-	/* Pages under I/O have been copied to head->rc_pages.
-	 * Prevent their premature release by svc_xprt_release() .
-	 */
-	for (i = 0; i < info->ri_readctxt->rc_page_count; i++)
-		rqstp->rq_pages[i] = NULL;
-
 	return ret;
 }
 
@@ -807,6 +800,26 @@ static int svc_rdma_build_pz_read_chunk(struct svc_rqst *rqstp,
 	return ret;
 }
 
+/* Pages under I/O have been copied to head->rc_pages. Ensure they
+ * are not released by svc_xprt_release() until the I/O is complete.
+ *
+ * This has to be done after all Read WRs are constructed to properly
+ * handle a page that is part of I/O on behalf of two different RDMA
+ * segments.
+ *
+ * Do this only if I/O has been posted. Otherwise, we do indeed want
+ * svc_xprt_release() to clean things up properly.
+ */
+static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
+				   const unsigned int start,
+				   const unsigned int num_pages)
+{
+	unsigned int i;
+
+	for (i = start; i < num_pages + start; i++)
+		rqstp->rq_pages[i] = NULL;
+}
+
 /**
  * svc_rdma_recv_read_chunk - Pull a Read chunk from the client
  * @rdma: controlling RDMA transport
@@ -860,6 +873,7 @@ int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
 	ret = svc_rdma_post_chunk_ctxt(&info->ri_cc);
 	if (ret < 0)
 		goto out_err;
+	svc_rdma_save_io_pages(rqstp, 0, head->rc_page_count);
 	return 0;
 
 out_err: