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Fri, 19 Jun 2026 00:55:36 -0700 (PDT) Received: from [127.0.1.1] ([47.253.114.73]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c7209bc296sm15297755ad.49.2026.06.19.00.55.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2026 00:55:36 -0700 (PDT) From: Wayen Yan To: netdev@vger.kernel.org Cc: lorenzo@kernel.org, horms@kernel.org, pabeni@redhat.com, kuba@kernel.org, edumazet@google.com, andrew+netdev@lunn.ch, angelogioacchino.delregno@collabora.com, matthias.bgg@gmail.com, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org Subject: [PATCH net v4] net: airoha: Fix skb->priority underflow in airoha_dev_select_queue() Date: Fri, 19 Jun 2026 15:50:16 +0800 Message-ID: <178185573207.2378135.3729126358670287878@gmail.com> Content-Type: text/plain; charset=utf-8 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In airoha_dev_select_queue(), the expression: queue = (skb->priority - 1) % AIROHA_NUM_QOS_QUEUES; implicitly converts to unsigned arithmetic: when skb->priority is 0 (the default for unclassified traffic), (0u - 1u) wraps to UINT_MAX, and UINT_MAX % 8 = 7, routing default best-effort packets to the highest-priority QoS queue. This causes QoS inversion where the majority of traffic on a PON gateway starves actual high-priority flows (VoIP, gaming, etc.). The "- 1" offset was a leftover from the ETS offload implementation that has since been removed. The correct mapping is a direct modulo: queue = skb->priority % AIROHA_NUM_QOS_QUEUES; This maps priority 0 → queue 0 (lowest), priority 7 → queue 7 (highest), with higher priorities wrapping around. This is the standard Linux sk_prio → HW queue mapping used by other drivers. Fixes: 2b288b81560b ("net: airoha: Introduce ndo_select_queue callback") Acked-by: Lorenzo Bianconi Reviewed-by: Joe Damato Signed-off-by: Wayen Yan --- Changes in v4: - Remove the "- 1" offset entirely as suggested by Lorenzo and Jakub. The offset was an ETS offload leftover; the correct mapping is a direct modulo of skb->priority to AIROHA_NUM_QOS_QUEUES, matching the standard Linux sk_prio → HW queue convention. (v3 used a ternary guard which addressed the underflow but kept the unneeded offset.) Link: https://lore.kernel.org/netdev/20260617164448.31e189bc@kernel.org/ Link: https://lore.kernel.org/netdev/ajPCgH7E_ke6Fdur@lore-desk/ drivers/net/ethernet/airoha/airoha_eth.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/net/ethernet/airoha/airoha_eth.c b/drivers/net/ethernet/airoha/airoha_eth.c index d0c0c0ec8a..9ec3f22754 100644 --- a/drivers/net/ethernet/airoha/airoha_eth.c +++ b/drivers/net/ethernet/airoha/airoha_eth.c @@ -1928,7 +1928,7 @@ static u16 airoha_dev_select_queue(struct net_device *dev, struct sk_buff *skb, */ channel = netdev_uses_dsa(dev) ? skb_get_queue_mapping(skb) : port->id; channel = channel % AIROHA_NUM_QOS_CHANNELS; - queue = (skb->priority - 1) % AIROHA_NUM_QOS_QUEUES; /* QoS queue */ + queue = skb->priority % AIROHA_NUM_QOS_QUEUES; queue = channel * AIROHA_NUM_QOS_QUEUES + queue; return queue < dev->num_tx_queues ? queue : 0; -- 2.51.0