+ Linus

On Mon, Aug 04, 2025 at 11:00:50AM +0100, Simon Horman wrote:

+ John Ernberg

On Sat, Aug 02, 2025 at 02:03:10AM +0700, Ammar Faizi wrote:

quoted

The commit in the Fixes tag breaks my laptop (found by git bisect).
My home RJ45 LAN cable cannot connect after that commit.

The call to netif_carrier_on() should be done when netif_carrier_ok()
is false. Not when it's true. Because calling netif_carrier_on() when
__LINK_STATE_NOCARRIER is not set actually does nothing.

Cc: Armando Budianto <redacted>
Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/netdev/0752dee6-43d6-4e1f-81d2-4248142cccd2@gnuweeb.org (local)
Fixes: 0d9cfc9b8cb1 ("net: usbnet: Avoid potential RCU stall on LINK_CHANGE event")
Signed-off-by: Ammar Faizi <redacted>
---

v2:
  - Rebase on top of the latest netdev/net tree. The previous patch was
    based on 0d9cfc9b8cb1. Line numbers have changed since then.

 drivers/net/usb/usbnet.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

It seems this has escalated a bit as it broke things for Linus while
he was travelling. He tested this patch and it resolved the problem.
Which I think counts for something.

https://lore.kernel.org/netdev/CAHk-=wgkvNuGCDUMMs9bW9Mz5o=LcMhcDK_b2ThO6_T7cquoEQ@mail.gmail.com/ (local)

I have looked over the patch and it appears to me that it addresses a
straightforward logic error: a check was added to turn the carrier on only
if it is already on. Which seems a bit nonsensical. And presumably the
intention was to add the check for the opposite case.

This patch addresses that problem.

So let me try and nudge this on a bit by providing a tag.

Reviewed-by: Simon Horman <horms@kernel.org>

quoted

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index a38ffbf4b3f0..a1827684b92c 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c

@@ -1114,31 +1114,31 @@ static const struct ethtool_ops usbnet_ethtool_ops = {
 };
 
 /*-------------------------------------------------------------------------*/
 
 static void __handle_link_change(struct usbnet *dev)
 {
 	if (!test_bit(EVENT_DEV_OPEN, &dev->flags))
 		return;
 
 	if (!netif_carrier_ok(dev->net)) {
+		if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
+			netif_carrier_on(dev->net);
+
 		/* kill URBs for reading packets to save bus bandwidth */
 		unlink_urbs(dev, &dev->rxq);
 
 		/*
 		 * tx_timeout will unlink URBs for sending packets and
 		 * tx queue is stopped by netcore after link becomes off
 		 */
 	} else {
-		if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
-			netif_carrier_on(dev->net);
-
 		/* submitting URBs for reading packets */
 		queue_work(system_bh_wq, &dev->bh_work);
 	}
 
 	/* hard_mtu or rx_urb_size may change during link change */
 	usbnet_update_max_qlen(dev);
 
 	clear_bit(EVENT_LINK_CHANGE, &dev->flags);
 }
 

-- 
Ammar Faizi