From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59F17C433F5 for ; Mon, 24 Jan 2022 19:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347653AbiAXTi3 (ORCPT ); Mon, 24 Jan 2022 14:38:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52664 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352462AbiAXTab (ORCPT ); Mon, 24 Jan 2022 14:30:31 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EEB81C029830; Mon, 24 Jan 2022 11:13:53 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 77FA46090A; Mon, 24 Jan 2022 19:13:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F8F3C340E5; Mon, 24 Jan 2022 19:13:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643051632; bh=zjFhddV6fMo/XM9nnuuK90VsKmvyM28pHTpGTioDg3o=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NREVZplD9evTi1zOzP/QsNuiMZzQOeP/5wf6H27lkPjPuHq3d53r1pl+/R90crVhp +heKURdbIT9HjY7ovZYqZvdO1weH0sWloAdVztmKaJsJC1A0pj00F5gLBCQGztWPA0 vYH5qKmyjoy+JTXEPz6PjTrrn8oPG4kmZjlg1Zko= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Laurent Bernaille , Daniel Borkmann , Maciej Fijalkowski , Toshiaki Makita , Eric Dumazet , Paolo Abeni , John Fastabend , Willem de Bruijn , Eric Dumazet , "David S. Miller" Subject: [PATCH 4.19 005/239] veth: Do not record rx queue hint in veth_xmit Date: Mon, 24 Jan 2022 19:40:43 +0100 Message-Id: <20220124183943.285108675@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124183943.102762895@linuxfoundation.org> References: <20220124183943.102762895@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Daniel Borkmann commit 710ad98c363a66a0cd8526465426c5c5f8377ee0 upstream. Laurent reported that they have seen a significant amount of TCP retransmissions at high throughput from applications residing in network namespaces talking to the outside world via veths. The drops were seen on the qdisc layer (fq_codel, as per systemd default) of the phys device such as ena or virtio_net due to all traffic hitting a _single_ TX queue _despite_ multi-queue device. (Note that the setup was _not_ using XDP on veths as the issue is generic.) More specifically, after edbea9220251 ("veth: Store queue_mapping independently of XDP prog presence") which made it all the way back to v4.19.184+, skb_record_rx_queue() would set skb->queue_mapping to 1 (given 1 RX and 1 TX queue by default for veths) instead of leaving at 0. This is eventually retained and callbacks like ena_select_queue() will also pick single queue via netdev_core_pick_tx()'s ndo_select_queue() once all the traffic is forwarded to that device via upper stack or other means. Similarly, for others not implementing ndo_select_queue() if XPS is disabled, netdev_pick_tx() might call into the skb_tx_hash() and check for prior skb_rx_queue_recorded() as well. In general, it is a _bad_ idea for virtual devices like veth to mess around with queue selection [by default]. Given dev->real_num_tx_queues is by default 1, the skb->queue_mapping was left untouched, and so prior to edbea9220251 the netdev_core_pick_tx() could do its job upon __dev_queue_xmit() on the phys device. Unbreak this and restore prior behavior by removing the skb_record_rx_queue() from veth_xmit() altogether. If the veth peer has an XDP program attached, then it would return the first RX queue index in xdp_md->rx_queue_index (unless configured in non-default manner). However, this is still better than breaking the generic case. Fixes: edbea9220251 ("veth: Store queue_mapping independently of XDP prog presence") Fixes: 638264dc9022 ("veth: Support per queue XDP ring") Reported-by: Laurent Bernaille Signed-off-by: Daniel Borkmann Cc: Maciej Fijalkowski Cc: Toshiaki Makita Cc: Eric Dumazet Cc: Paolo Abeni Cc: John Fastabend Cc: Willem de Bruijn Acked-by: John Fastabend Reviewed-by: Eric Dumazet Acked-by: Toshiaki Makita Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- drivers/net/veth.c | 1 - 1 file changed, 1 deletion(-) --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -197,7 +197,6 @@ static netdev_tx_t veth_xmit(struct sk_b if (rxq < rcv->real_num_rx_queues) { rq = &rcv_priv->rq[rxq]; rcv_xdp = rcu_access_pointer(rq->xdp_prog); - skb_record_rx_queue(skb, rxq); } if (likely(veth_forward_skb(rcv, skb, rq, rcv_xdp) == NET_RX_SUCCESS)) {