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 6120840FDAD; Wed, 29 Apr 2026 17:21:28 +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=1777483288; cv=none; b=NmzgbEVZ5aKxgaHnh8O+7TDcVYG+mQK7HgZvIupGRPUvmNAc3tQrkXHnAlvmY+C57w8Nx77wf+2hiM1BE5vgm8izFJjP/Kjwh/ivOij915kXnuMgaVVJTuSX7wnWzaxwCJET20labH1tFBzPhdYsk8LluSbLNi+OLJ8SKiod15U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777483288; c=relaxed/simple; bh=gb8XJrhOM7OyaOgd25hPYdSzkbBzhMyrw+KarXVSWas=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=mTrwtx8bnsTy8rbiMYNLvikZT1k14U8FkOLgaJ2p0zgtT5b4CBE9X1GJ5H39vtGonAl36PksMtqdcoIlb1p0JJX0BK+dieFpseFYAYuk7NaMewPchLv34P9d5kTElnLbPFQHmgfmhPupW0UCmGVqq8eJpm1EeYztBvAMxhKpYRc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=t6AROYrr; 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="t6AROYrr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 29485C2BCB8; Wed, 29 Apr 2026 17:21:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777483288; bh=gb8XJrhOM7OyaOgd25hPYdSzkbBzhMyrw+KarXVSWas=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=t6AROYrrEC8WYQK7q5MEgFPqxh5OfU7Quppx2hbSMZHonkGmbcdUnBV+NsWyF7kfW uMOWxOAaEk407f983AC9x4wx7azewxwdaj/oFdEcffxLUwo/phc76U2riZxXa3NkW9 B5HXLUqU4c9Pvhjr1+WO+Nb0Na7yuVfQqEkGmp0RazVY05TkhFqbpRB1VtoOeiapdT lrNwQrTw01ufd6dPRQYh/etCZNRx+yrzbisxvIA70LH1AUnsfrWT9jTVvroRoX9v8u Log6p81e7SYF63SeFkhEv+Bf/38+TwhxQMIozbZtwYFM792aBT/WwCtuagIsgwNzER 6y1kOh3b3u2/g== From: hawk@kernel.org To: netdev@vger.kernel.org Cc: hawk@kernel.org, kernel-team@cloudflare.com, =?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 v3 3/5] veth: add tx_timeout watchdog as BQL safety net Date: Wed, 29 Apr 2026 19:20:30 +0200 Message-ID: <20260429172036.1028526-4-hawk@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260429172036.1028526-1-hawk@kernel.org> References: <20260429172036.1028526-1-hawk@kernel.org> Precedence: bulk X-Mailing-List: netdev@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 3de25ba34a90..9d7b085c9548 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -1431,6 +1431,22 @@ 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); @@ -1769,6 +1785,7 @@ 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 = { @@ -1808,6 +1825,7 @@ 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