From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C1B62770A; Mon, 13 Apr 2026 09:45:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776073530; cv=none; b=SyvnyQqCkczrl8hFsiUEU64sQcWrM8tUKSm3C8ueZQpvF8IjZBdXIXItAgDlGsdC8++lmJbF2lba3D7QVdEEfpAQdQ1W7V/24UbP3u4Tan02FHboLuGqUbLT+9w7SujsNAflmv7MaWOMV3/Sig5v4FRft0cxN/vtr48adrIgd/c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776073530; c=relaxed/simple; bh=pjopUZqbocG7BT/UYcHtL5CE4WwMGAOUPy2Z5SCAngs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=OBtGbM2DhEM1aqeSWGw2JF3I+jmPeCFBaDWgeZ9CZVWliwPYWpYkaQgu8MeSiR4CfPghPAUVmV88W7dm5R59zo6PiuI+JzZleLRoQ7RIizwaCV8PU5TeMaJXS2qUP5AkG/koIaqZ9Pjtw50NYV4cyx8pNwpi0T9/PoQqOCLj8S8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=J65axTSf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="J65axTSf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9DF5C2BCB1; Mon, 13 Apr 2026 09:45:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776073530; bh=pjopUZqbocG7BT/UYcHtL5CE4WwMGAOUPy2Z5SCAngs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J65axTSfyYNGw182Le90KbptgzSIEn/goFzcxYd9aJK1begyY/qojhGwzHNk4AiQ1 AcAIEA24Q6mqhCggtXFu3DwfjiJiSRu1mR7kCdst0ocB5Jk3DFlDqm/ILqlp8E00tk S1F3+Mkd8bzO8wPiyTpaHfkRMz6CFY7GZR0OgwTc7LUwCfTJRU0wsy2pD3lh7kPLCJ 4F4+kRr49RPyow/a5asGkS/EZ4txKeVCtBQQd0cFFezU2uMhgEu9tc/MuVAto1Uwya KeAFqGxAvYLv532R8jwZ2ddNY+UNUl0F3025zDCDeifOndJSWOtfJ8fFeFPVHZGqmW BPXV4nWrX1RiQ== From: hawk@kernel.org To: netdev@vger.kernel.org Cc: kernel-team@cloudflare.com, Jesper Dangaard Brouer , =?UTF-8?q?Jonas=20K=C3=B6ppeler?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org Subject: [PATCH net-next v2 3/5] veth: add tx_timeout watchdog as BQL safety net Date: Mon, 13 Apr 2026 11:44:36 +0200 Message-ID: <20260413094442.1376022-4-hawk@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260413094442.1376022-1-hawk@kernel.org> References: <20260413094442.1376022-1-hawk@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Jesper Dangaard Brouer With the introduction of BQL (Byte Queue Limits) for veth, there are now two independent mechanisms that can stop a transmit queue: - DRV_XOFF: set by netif_tx_stop_queue() when the ptr_ring is full - STACK_XOFF: set by BQL when the byte-in-flight limit is reached If either mechanism stalls without a corresponding wake/completion, the queue stops permanently. Enable the net device watchdog timer and implement ndo_tx_timeout as a failsafe recovery. The timeout handler resets BQL state (clearing STACK_XOFF) and wakes the queue (clearing DRV_XOFF), covering both stop mechanisms. The watchdog fires after 16 seconds, which accommodates worst-case NAPI processing (budget=64 packets x 250ms per-packet consumer delay) without false positives under normal backpressure. Signed-off-by: Jesper Dangaard Brouer Tested-by: Jonas Köppeler --- drivers/net/veth.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index 6431dc40f9b4..911e7e36e166 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -1429,6 +1429,22 @@ static int veth_set_channels(struct net_device *dev, goto out; } +static void veth_tx_timeout(struct net_device *dev, unsigned int txqueue) +{ + struct netdev_queue *txq = netdev_get_tx_queue(dev, txqueue); + + netdev_err(dev, + "veth backpressure(0x%lX) stalled(n:%ld) TXQ(%u) re-enable\n", + txq->state, atomic_long_read(&txq->trans_timeout), txqueue); + + /* Cannot call netdev_tx_reset_queue(): dql_reset() races with + * peer NAPI calling dql_completed() concurrently. + * Just clear the stop bits; the qdisc will re-stop if still stuck. + */ + clear_bit(__QUEUE_STATE_STACK_XOFF, &txq->state); + netif_tx_wake_queue(txq); +} + static int veth_open(struct net_device *dev) { struct veth_priv *priv = netdev_priv(dev); @@ -1767,6 +1783,7 @@ static const struct net_device_ops veth_netdev_ops = { .ndo_bpf = veth_xdp, .ndo_xdp_xmit = veth_ndo_xdp_xmit, .ndo_get_peer_dev = veth_peer_dev, + .ndo_tx_timeout = veth_tx_timeout, }; static const struct xdp_metadata_ops veth_xdp_metadata_ops = { @@ -1806,6 +1823,7 @@ static void veth_setup(struct net_device *dev) dev->priv_destructor = veth_dev_free; dev->pcpu_stat_type = NETDEV_PCPU_STAT_TSTATS; dev->max_mtu = ETH_MAX_MTU; + dev->watchdog_timeo = msecs_to_jiffies(16000); dev->hw_features = VETH_FEATURES; dev->hw_enc_features = VETH_FEATURES; -- 2.43.0