NFS: Fix up return value on fatal errors in nfs_page_async_flush()

Ensure that we return the fatal error value that caused us to exit
nfs_page_async_flush().

Fixes: c373fff7 ("NFSv4: Don't special case "launder"")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: stable@vger.kernel.org # v4.12+
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/write.c

@@ -621,11 +621,12 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
 	nfs_set_page_writeback(page);
 	WARN_ON_ONCE(test_bit(PG_CLEAN, &req->wb_flags));
 
-	ret = 0;
+	ret = req->wb_context->error;
 	/* If there is a fatal error that covers this write, just exit */
-	if (nfs_error_is_fatal_on_server(req->wb_context->error))
+	if (nfs_error_is_fatal_on_server(ret))
 		goto out_launder;
 
+	ret = 0;
 	if (!nfs_pageio_add_request(pgio, req)) {
 		ret = pgio->pg_error;
 		/*
@@ -635,9 +636,9 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
 			nfs_context_set_write_error(req->wb_context, ret);
 			if (nfs_error_is_fatal_on_server(ret))
 				goto out_launder;
-		}
+		} else
+			ret = -EAGAIN;
 		nfs_redirty_request(req);
-		ret = -EAGAIN;
 	} else
 		nfs_add_stats(page_file_mapping(page)->host,
 				NFSIOS_WRITEPAGES, 1);