From nobody Fri Dec 19 15:49:11 2025 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 CC36833BBA8; Wed, 5 Nov 2025 17:28:18 +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=1762363698; cv=none; b=V0V00yfMMXEJG8kuZg+NuOJjTURFXsPqF1KJ+DR8dJQhoEgu3PVO9rJwycV5IbwnVLFNm/jtfjh9+nRdaiphGK+zaZF9SVvqiN/OT2MjQ/s48P7M6/dDYch0DKsun/iHJKcG8u9t7BFOvoXFv3fTJnCSCpECWOhV8RlomXnjUCw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762363698; c=relaxed/simple; bh=qBxeUGo0ojlcdD0EQyP1rqmZRW7Xn9CXpQtmjLZHoB0=; h=Subject:From:To:Cc:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=k1st348h3X3rruqvcK50jOkFi5XLOg039PAuNOzLx74J8UEIh8VVJIA7aSnXH3XPBTTLTnQOFSwAKKTBF+iHB7RIZzEMjW50bBZqm4UzvXZSnus2CKQ1fO9Qhedw4/19WjXeWLylkcnM41XHeI5Crqv4RyqQ7JUWf+4CGbr0mL4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GA9epBiG; 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="GA9epBiG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F358C116B1; Wed, 5 Nov 2025 17:28:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762363698; bh=qBxeUGo0ojlcdD0EQyP1rqmZRW7Xn9CXpQtmjLZHoB0=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=GA9epBiGmB07XAPsrd6KyTHrW4yo49Q48S2PhkZCGqWDMQu8mlt+Irij0p76pLBAN 1dqk5mfppEWysjH1JlFifOkvVYqResdD2MhA0myvyzM0AMwznDCerASkaLLwpdWrqz jhXI2+MZIolN990eAk+1z9Paz/Pq6j0oM8HX6BB9X7XrpThBiBJn1FxtrhZnoxV5TC 6iCiNQzi5LOWsgjOtKb3s5/7t1jrmbQVTlFZuHyz712Pa2Ouy2Vgi6Ft8boRb/yOSG 1B5ElQ6771jeiRsPULU0yLtEEGfjbYfLwFvVo+Wwn/JHFmuMPQjrlHVugWsMf4tobU 3kbyNSS4/0RLg== Subject: [PATCH net V3 1/2] veth: enable dev_watchdog for detecting stalled TXQs From: Jesper Dangaard Brouer To: netdev@vger.kernel.org, =?utf-8?q?Toke_H=C3=B8iland-J=C3=B8rgensen?= Cc: Jesper Dangaard Brouer , Eric Dumazet , "David S. Miller" , Jakub Kicinski , Paolo Abeni , ihor.solodrai@linux.dev, "Michael S. Tsirkin" , makita.toshiaki@lab.ntt.co.jp, toshiaki.makita1@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel-team@cloudflare.com Date: Wed, 05 Nov 2025 18:28:12 +0100 Message-ID: <176236369293.30034.1875162194564877560.stgit@firesoul> In-Reply-To: <176236363962.30034.10275956147958212569.stgit@firesoul> References: <176236363962.30034.10275956147958212569.stgit@firesoul> User-Agent: StGit/1.5 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: quoted-printable The changes introduced in commit dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops") have been found to cause a race condition in production environments. Under specific circumstances, observed exclusively on ARM64 (aarch64) systems with Ampere Altra Max CPUs, a transmit queue (TXQ) can become permanently stalled. This happens when the race condition leads to the TXQ entering the QUEUE_STATE_DRV_XOFF state without a corresponding queue wake-= up, preventing the attached qdisc from dequeueing packets and causing the network link to halt. As a first step towards resolving this issue, this patch introduces a failsafe mechanism. It enables the net device watchdog by setting a timeout value and implements the .ndo_tx_timeout callback. If a TXQ stalls, the watchdog will trigger the veth_tx_timeout() function, which logs a warning and calls netif_tx_wake_queue() to unstall the queue and allow traffic to resume. The log message will look like this: veth42: NETDEV WATCHDOG: CPU: 34: transmit queue 0 timed out 5393 ms veth42: veth backpressure stalled(n:1) TXQ(0) re-enable This provides a necessary recovery mechanism while the underlying race condition is investigated further. Subsequent patches will address the root cause and add more robust state handling. Fixes: dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to re= duce TX drops") Reviewed-by: Toke H=C3=B8iland-J=C3=B8rgensen Signed-off-by: Jesper Dangaard Brouer --- drivers/net/veth.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/drivers/net/veth.c b/drivers/net/veth.c index a3046142cb8e..7b1a9805b270 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -959,8 +959,10 @@ static int veth_xdp_rcv(struct veth_rq *rq, int budget, rq->stats.vs.xdp_packets +=3D done; u64_stats_update_end(&rq->stats.syncp); =20 - if (peer_txq && unlikely(netif_tx_queue_stopped(peer_txq))) + if (peer_txq && unlikely(netif_tx_queue_stopped(peer_txq))) { + txq_trans_cond_update(peer_txq); netif_tx_wake_queue(peer_txq); + } =20 return done; } @@ -1373,6 +1375,16 @@ static int veth_set_channels(struct net_device *dev, goto out; } =20 +static void veth_tx_timeout(struct net_device *dev, unsigned int txqueue) +{ + struct netdev_queue *txq =3D netdev_get_tx_queue(dev, txqueue); + + netdev_err(dev, "veth backpressure stalled(n:%ld) TXQ(%u) re-enable\n", + atomic_long_read(&txq->trans_timeout), txqueue); + + netif_tx_wake_queue(txq); +} + static int veth_open(struct net_device *dev) { struct veth_priv *priv =3D netdev_priv(dev); @@ -1711,6 +1723,7 @@ static const struct net_device_ops veth_netdev_ops = =3D { .ndo_bpf =3D veth_xdp, .ndo_xdp_xmit =3D veth_ndo_xdp_xmit, .ndo_get_peer_dev =3D veth_peer_dev, + .ndo_tx_timeout =3D veth_tx_timeout, }; =20 static const struct xdp_metadata_ops veth_xdp_metadata_ops =3D { @@ -1749,6 +1762,7 @@ static void veth_setup(struct net_device *dev) dev->priv_destructor =3D veth_dev_free; dev->pcpu_stat_type =3D NETDEV_PCPU_STAT_TSTATS; dev->max_mtu =3D ETH_MAX_MTU; + dev->watchdog_timeo =3D msecs_to_jiffies(5000); =20 dev->hw_features =3D VETH_FEATURES; dev->hw_enc_features =3D VETH_FEATURES;