The commit referenced in the Fixes tag causes usbnet to malfunction
(identified via git bisect). Post-commit, my external RJ45 LAN cable
fails to connect. Linus also reported the same issue after pulling that
commit.

The code has a logic error: netif_carrier_on() is only called when the
link is already on. Fix this by moving the netif_carrier_on() call
outside the if-statement entirely. This ensures it is always called
when EVENT_LINK_CARRIER_ON is set and properly clears it regardless
of the link state.

Cc: stable@vger.kernel.org
Cc: Armando Budianto <sprite@gnuweeb.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/all/CAHk-=wjqL4uF0MG_c8+xHX1Vv8==sPYQrtzbdA3kzi96284nuQ@mail.gmail.com
Closes: https://lore.kernel.org/netdev/CAHk-=wjKh8X4PT_mU1kD4GQrbjivMfPn-_hXa6han_BTDcXddw@mail.gmail.com
Closes: https://lore.kernel.org/netdev/0752dee6-43d6-4e1f-81d2-4248142cccd2@gnuweeb.org
Fixes: 0d9cfc9b8cb1 ("net: usbnet: Avoid potential RCU stall on LINK_CHANGE event")
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

v3:
  - Move the netif_carrier_on() call outside of the if-statement
    entirely (Linus).

v2:
  - Rebase on top of the latest netdev/net tree. The previous patch was
    based on 0d9cfc9b8cb1. Line numbers have changed since then.
  Link: https://lore.gnuweeb.org/gwml/20250801190310.58443-1-ammarfaizi2@gnuweeb.org

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

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index a38ffbf4b3f0..511c4154cf74 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1113,32 +1113,32 @@ static const struct ethtool_ops usbnet_ethtool_ops = {
 	.set_link_ksettings	= usbnet_set_link_ksettings_mii,
 };
 
 /*-------------------------------------------------------------------------*/
 
 static void __handle_link_change(struct usbnet *dev)
 {
 	if (!test_bit(EVENT_DEV_OPEN, &dev->flags))
 		return;
 
+	if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
+		netif_carrier_on(dev->net);
+
 	if (!netif_carrier_ok(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

On Wed, Aug 06, 2025 at 07:31:05AM +0700, Ammar Faizi wrote:
> The commit referenced in the Fixes tag causes usbnet to malfunction
> (identified via git bisect). Post-commit, my external RJ45 LAN cable
> fails to connect. Linus also reported the same issue after pulling that
> commit.
> 
> The code has a logic error: netif_carrier_on() is only called when the
> link is already on. Fix this by moving the netif_carrier_on() call
> outside the if-statement entirely. This ensures it is always called
> when EVENT_LINK_CARRIER_ON is set and properly clears it regardless
> of the link state.
> 
> Cc: stable@vger.kernel.org
> Cc: Armando Budianto <sprite@gnuweeb.org>
> Reviewed-by: Simon Horman <horms@kernel.org>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Link: https://lore.kernel.org/all/CAHk-=wjqL4uF0MG_c8+xHX1Vv8==sPYQrtzbdA3kzi96284nuQ@mail.gmail.com
> Closes: https://lore.kernel.org/netdev/CAHk-=wjKh8X4PT_mU1kD4GQrbjivMfPn-_hXa6han_BTDcXddw@mail.gmail.com
> Closes: https://lore.kernel.org/netdev/0752dee6-43d6-4e1f-81d2-4248142cccd2@gnuweeb.org
> Fixes: 0d9cfc9b8cb1 ("net: usbnet: Avoid potential RCU stall on LINK_CHANGE event")
> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>

FTR, this patch was applied directly by Linus:

- net: usbnet: Fix the wrong netif_carrier_on() call
  https://git.kernel.org/torvalds/c/8466d393700f