[PATCH net] usbnet: fix crash due to missing BQL accounting after resume

[Simon Schippers]

In commit 7ff14c52049e ("usbnet: Add support for Byte Queue Limits
(BQL)"), it was missed that usbnet_resume() may enqueue SKBs using
__skb_queue_tail() without reporting them to BQL. As a result, the next
call to netdev_completed_queue() triggers a BUG_ON() in dql_completed(),
since the SKBs queued during resume were never accounted for.

This patch fixes the issue by adding a corresponding netdev_sent_queue()
call in usbnet_resume() when SKBs are queued after suspend. Because
dev->txq.lock is held at this point, no concurrent calls to
netdev_sent_queue() from usbnet_start_xmit() can occur.

The crash can be reproduced by generating network traffic
(e.g. iperf3 -c ... -t 0), suspending the system, and then waking it up
(e.g. rtcwake -m mem -s 5).

When testing USB2 Android tethering (cdc_ncm), the system crashed within
three suspend/resume cycles without this patch. With the patch applied,
no crashes were observed after 90 cycles. Testing with an AX88179 USB
Ethernet adapter also showed no crashes.

Reported-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
Tested-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
Tested-by: Simon Schippers <simon.schippers@xxxxxxxxxxxxxx>
Signed-off-by: Simon Schippers <simon.schippers@xxxxxxxxxxxxxx>
---
 drivers/net/usb/usbnet.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 36742e64cff7..35789ff4dd55 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1984,6 +1984,7 @@ int usbnet_resume(struct usb_interface *intf)
 			} else {
 				netif_trans_update(dev->net);
 				__skb_queue_tail(&dev->txq, skb);
+				netdev_sent_queue(dev->net, skb->len);
 			}
 		}
 
-- 
2.43.0