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 E3CC147CC84; Tue, 5 May 2026 13:22:23 +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=1777987344; cv=none; b=DGaAKi9Pgur91eDp7S2iGzjA3wnv/7pLy8dNS6WyOKrLWDe9mbySPv7WqefCbIc49u+yOGQRMjYXmGAePRZKByNOCA0nuGga0mzTU6qwNrEmXrmUAmO1Uu1P/U3KpmIBo5I/lB4TlQfaANa+YmbqzVPCj272WUwZnj71qc3F8vU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777987344; c=relaxed/simple; bh=LB5PthOb3W1gdqxwjDr6F75P1lpC1n8DPti/KatVVHI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=tLDNg5/VkbeItIUtCRQq0IBR3Oz5MhiYgeCQK9miLxEz/j274K/I1FE+/umaOK+RCbwVOfx0a9251zA/Zp/m5tn/kWa2G43GO2lfpqqYwb97lBSub19CCOM27MKA3lokWjdJNSja1GgnLDBsN3RNVdKUUIjkDJBv1JWwSx+tPno= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eV8enOOn; 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="eV8enOOn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50335C2BCB4; Tue, 5 May 2026 13:22:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777987343; bh=LB5PthOb3W1gdqxwjDr6F75P1lpC1n8DPti/KatVVHI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eV8enOOnmpTqXxC7Fn8EoSIWAYDJDi2A3wpBZa0SRNrZNWvwRfQKRBMB9tLz7mp+V cgfpZnG4ugSqZHgr+8w3TykrkisPbQU50sHNMI7hPpiECoLkSMdi9SgRo4KqZnXSxz cfiGw8lm3ds+G/cU2rzlOtTRhQZnyIzncK7uqzPax9kBGYOY/5DF7tXtDYqbvZ7BHN QTnDChVEm23duCCgNZG9mYdF7zNAU4GHjA/bekANpl0Z6w52X57t8KiZI+VqOI6VrY /n1wNvNU07LiQcSyaOVozExFAdSAH6THAXNCiX7AhZORbVKTAoXgIhPo/C25QTmtd/ TA1QrjO/zh4Hg== 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 v5 4/5] veth: add tx_timeout watchdog as BQL safety net Date: Tue, 5 May 2026 15:21:56 +0200 Message-ID: <20260505132159.241305-5-hawk@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260505132159.241305-1-hawk@kernel.org> References: <20260505132159.241305-1-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 86b78900c48e..4103d298aa9b 100644 --- a/drivers/net/veth.c +++ b/drivers/net/veth.c @@ -1442,6 +1442,22 @@ 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); @@ -1780,6 +1796,7 @@ 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 = { @@ -1819,6 +1836,7 @@ 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