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Wed, 07 Oct 2026 04:36:25 -0700 (PDT) Received: from LAPTOP-450UDG4J ([223.185.133.64]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-16168f586f8sm8680304c88.13.2026.10.07.04.36.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Oct 2026 04:36:24 -0700 (PDT) From: Yogesh Gaur To: Marc Kleine-Budde , Vincent Mailhol Cc: linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, Yogesh Gaur , syzbot+937a3a1fbfbc99d6fcaf@syzkaller.appspotmail.com Subject: [PATCH] can: vcan: use per-CPU device stats Date: Wed, 7 Oct 2026 17:06:11 +0530 Message-ID: <20261007113611.2082-1-yogeshgaur.83@gmail.com> X-Mailer: git-send-email 2.55.0.windows.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit vcan_tx() and vcan_rx() update dev->stats with plain increments and rely on the tx queue lock to serialise them. That only holds for a single tx queue. vcan does not implement get_num_tx_queues(), so rtnl_create_link() honours IFLA_NUM_TX_QUEUES and a vcan device can be created with several queues, each with its own xmit lock. Two CPUs transmitting on different queues then update the same counters concurrently and lose increments: BUG: KCSAN: data-race in vcan_tx / vcan_tx read-write to 0xffff88811aad8228 of 8 bytes by interrupt on cpu 1: vcan_tx+0x325/0x5d0 drivers/net/can/vcan.c:110 dev_hard_start_xmit+0x10c/0x380 net/core/dev.c:3969 __dev_queue_xmit+0xbfd/0x1ec0 net/core/dev.c:4958 can_send+0x584/0x720 net/can/af_can.c:279 bcm_can_tx+0x3ba/0x5b0 net/can/bcm.c:367 read-write to 0xffff88811aad8228 of 8 bytes by interrupt on cpu 0: vcan_tx+0x325/0x5d0 drivers/net/can/vcan.c:110 value changed: 0x00000000000025ef -> 0x00000000000025f0 Switch the packet and byte counters to the core's per-CPU dstats. The core allocates them for NETDEV_PCPU_STAT_DSTATS and folds them together with dev->stats in dev_get_stats(), so tx_dropped from can_dropped_invalid_skb() is still reported. Reported-by: syzbot+937a3a1fbfbc99d6fcaf@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=937a3a1fbfbc99d6fcaf Assisted-by: LLM Signed-off-by: Yogesh Gaur --- drivers/net/can/vcan.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/drivers/net/can/vcan.c b/drivers/net/can/vcan.c index 76e6b7b5c6a1..2ff90cb7eee9 100644 --- a/drivers/net/can/vcan.c +++ b/drivers/net/can/vcan.c @@ -71,10 +71,7 @@ MODULE_PARM_DESC(echo, "Echo sent frames (for testing). Default: 0 (Off)"); static void vcan_rx(struct sk_buff *skb, struct net_device *dev) { - struct net_device_stats *stats = &dev->stats; - - stats->rx_packets++; - stats->rx_bytes += can_skb_get_data_len(skb); + dev_dstats_rx_add(dev, can_skb_get_data_len(skb)); skb->pkt_type = PACKET_BROADCAST; skb->dev = dev; @@ -85,7 +82,6 @@ static void vcan_rx(struct sk_buff *skb, struct net_device *dev) static netdev_tx_t vcan_tx(struct sk_buff *skb, struct net_device *dev) { - struct net_device_stats *stats = &dev->stats; unsigned int len; int loop; @@ -93,8 +89,7 @@ static netdev_tx_t vcan_tx(struct sk_buff *skb, struct net_device *dev) return NETDEV_TX_OK; len = can_skb_get_data_len(skb); - stats->tx_packets++; - stats->tx_bytes += len; + dev_dstats_tx_add(dev, len); /* set flag whether this packet has to be looped back */ loop = skb->pkt_type == PACKET_LOOPBACK; @@ -107,8 +102,7 @@ static netdev_tx_t vcan_tx(struct sk_buff *skb, struct net_device *dev) /* only count the packets here, because the * CAN core already did the echo for us */ - stats->rx_packets++; - stats->rx_bytes += len; + dev_dstats_rx_add(dev, len); } consume_skb(skb); return NETDEV_TX_OK; @@ -185,6 +179,7 @@ static void vcan_setup(struct net_device *dev) dev->netdev_ops = &vcan_netdev_ops; dev->ethtool_ops = &vcan_ethtool_ops; dev->needs_free_netdev = true; + dev->pcpu_stat_type = NETDEV_PCPU_STAT_DSTATS; } static struct rtnl_link_ops vcan_link_ops __read_mostly = { -- 2.55.0.windows.5