From: Magnus Karlsson <magnus.karlsson@intel.com>
Date: Wed, 22 Sep 2021 09:56:08 +0200
Subject: selftests: xsk: Put the same buffer only once in the fill ring
Patch-mainline: v5.16-rc1
Git-commit: 872a1184dbf2b6ed9f435d6a37ad8007126da982
References: jsc#PED-1377

Fix a problem where the fill ring was populated with too many
entries. If number of buffers in the umem was smaller than the fill
ring size, the code used to loop over from the beginning of the umem
and start putting the same buffers in again. This is racy indeed as a
later packet can be received overwriting an earlier one before the Rx
thread manages to validate it.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210922075613.12186-9-magnus.karlsson@gmail.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/testing/selftests/bpf/xdpxceiver.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/tools/testing/selftests/bpf/xdpxceiver.c
+++ b/tools/testing/selftests/bpf/xdpxceiver.c
@@ -977,13 +977,18 @@ static void *worker_testapp_validate_tx(
 
 static void xsk_populate_fill_ring(struct xsk_umem_info *umem, struct pkt_stream *pkt_stream)
 {
-	u32 idx = 0, i;
+	u32 idx = 0, i, buffers_to_fill;
 	int ret;
 
-	ret = xsk_ring_prod__reserve(&umem->fq, XSK_RING_PROD__DEFAULT_NUM_DESCS, &idx);
-	if (ret != XSK_RING_PROD__DEFAULT_NUM_DESCS)
+	if (umem->num_frames < XSK_RING_PROD__DEFAULT_NUM_DESCS)
+		buffers_to_fill = umem->num_frames;
+	else
+		buffers_to_fill = XSK_RING_PROD__DEFAULT_NUM_DESCS;
+
+	ret = xsk_ring_prod__reserve(&umem->fq, buffers_to_fill, &idx);
+	if (ret != buffers_to_fill)
 		exit_with_error(ENOSPC);
-	for (i = 0; i < XSK_RING_PROD__DEFAULT_NUM_DESCS; i++) {
+	for (i = 0; i < buffers_to_fill; i++) {
 		u64 addr;
 
 		if (pkt_stream->use_addr_for_fill) {
@@ -993,12 +998,12 @@ static void xsk_populate_fill_ring(struc
 				break;
 			addr = pkt->addr;
 		} else {
-			addr = (i % umem->num_frames) * umem->frame_size + DEFAULT_OFFSET;
+			addr = i * umem->frame_size + DEFAULT_OFFSET;
 		}
 
 		*xsk_ring_prod__fill_addr(&umem->fq, idx++) = addr;
 	}
-	xsk_ring_prod__submit(&umem->fq, XSK_RING_PROD__DEFAULT_NUM_DESCS);
+	xsk_ring_prod__submit(&umem->fq, buffers_to_fill);
 }
 
 static void *worker_testapp_validate_rx(void *arg)