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Tue, 06 Oct 2026 05:08:39 -0700 (PDT) From: =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= To: netdev@vger.kernel.org Cc: oneukum@suse.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, =?UTF-8?q?=C3=96mer=20Mete=20Kaya?= Subject: [PATCH net v2] usbnet: fix EVENT_RX_PAUSED race in usbnet_skb_return() Date: Tue, 6 Oct 2026 15:07:04 +0300 Message-ID: <20261006120825.342164-1-omermetekaya0@gmail.com> X-Mailer: git-send-email 2.55.0 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 usbnet_resume_rx() disables local BHs before clearing EVENT_RX_PAUSED, but this does not synchronize with usbnet_skb_return() running on another CPU. On SMP, usbnet_skb_return() on CPU0 can pass the test_bit() check while CPU1 runs usbnet_resume_rx(), clears the flag and drains the queue, leaving the skb stranded in rxq_pause until the next MTU change or device stop. Fix with a double-check pattern: move clear_bit() in usbnet_resume_rx() under rxq_pause.lock; in usbnet_skb_return() take the lock and recheck the flag only on the slow path (unlikely paused), keeping the normal RX fast path lock-free. Fixes: 43daa96b166c ("usbnet: Stop RX Q on MTU change") Signed-off-by: Ömer Mete Kaya --- v2: Squash usbnet_resume_rx() fix into same patch; previous version only changed usbnet_skb_return() and was missing the clear_bit() change. drivers/net/usb/usbnet.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 84f97f448b2d..5eba2cef8bac 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -329,9 +329,14 @@ void usbnet_skb_return(struct usbnet *dev, struct sk_buff *skb) unsigned long flags; int status; - if (test_bit(EVENT_RX_PAUSED, &dev->flags)) { - skb_queue_tail(&dev->rxq_pause, skb); - return; + if (unlikely(test_bit(EVENT_RX_PAUSED, &dev->flags))) { + spin_lock_bh(&dev->rxq_pause.lock); + if (test_bit(EVENT_RX_PAUSED, &dev->flags)) { + __skb_queue_tail(&dev->rxq_pause, skb); + spin_unlock_bh(&dev->rxq_pause.lock); + return; + } + spin_unlock_bh(&dev->rxq_pause.lock); } /* only update if unset to allow minidriver rx_fixup override */ @@ -701,8 +706,9 @@ void usbnet_resume_rx(struct usbnet *dev) struct sk_buff *skb; int num = 0; - local_bh_disable(); + spin_lock_bh(&dev->rxq_pause.lock); clear_bit(EVENT_RX_PAUSED, &dev->flags); + spin_unlock_bh(&dev->rxq_pause.lock); while ((skb = skb_dequeue(&dev->rxq_pause)) != NULL) { usbnet_skb_return(dev, skb); @@ -710,7 +716,6 @@ void usbnet_resume_rx(struct usbnet *dev) } queue_work(system_bh_wq, &dev->bh_work); - local_bh_enable(); netif_dbg(dev, rx_status, dev->net, "paused rx queue disabled, %d skbs requeued\n", num); -- 2.55.0