From 60db47f02bfa2aa688938aa199117ec4f8e31d23 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Jonas=20K=C3=B6ppeler?= Date: Thu, 6 Aug 2026 13:43:49 +0200 Subject: [PATCH] veth: fix queue index used to wake the peer txq in veth_poll MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit veth_poll() derives the index of the peer TX queue to wake from rq->xdp_rxq.queue_index. That field is only initialized by xdp_rxq_info_reg() in veth_enable_xdp_range(), which runs only when an XDP program is attached. On the plain GRO/NAPI path (veth_napi_enable_range()) xdp_rxq_info_reg() is never called, so queue_index stays 0 for every queue, as priv->rq is zero-allocated. So in a multi-queue setup with GRO enabled and no XDP program attached, every NAPI instance looks at the peer's TX queue 0. If veth_xmit() stops peer TX queue 1 because the ptr_ring is full (NETDEV_TX_BUSY), nothing ever wakes it again: the poller draining queue 1 wakes queue 0 instead. veth implements no ndo_tx_timeout, so the netdev watchdog does not kick in either, and the queue stays stopped indefinitely. Derive the index from the position of the rq within priv->rq instead, which is correct regardless of whether XDP was ever enabled. Scripts to reproduce the stall are available at https://github.com/netoptimizer/veth-backpressure-performance-testing Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops") Signed-off-by: Jonas Köppeler Tested-by: Jesper Dangaard Brouer Acked-by: Jesper Dangaard Brouer Link: https://patch.msgid.link/20260806-veth-fix-poll-queue-idx-v1-1-c5357fb7573d@tu-berlin.de Signed-off-by: Jakub Kicinski --- drivers/net/veth.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index f80f6584a6ff..6ab84c837a33 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -967,7 +967,7 @@ static int veth_poll(struct napi_struct *napi, int budget) struct veth_rq *rq = container_of(napi, struct veth_rq, xdp_napi); struct veth_priv *priv = netdev_priv(rq->dev); - int queue_idx = rq->xdp_rxq.queue_index; + int queue_idx = rq - priv->rq; struct netdev_queue *peer_txq; struct veth_stats stats = {}; struct net_device *peer_dev; -- 2.47.3