Re: [PATCH net v2] net: usbnet: Fix the wrong netif_carrier_on() call placement

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, 5 Aug 2025 at 23:28, Simon Horman <horms@kernel.org> wrote:
>
> 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 I agree that there was a logic error.

I'm not 100% sure about the "straightforward" part.

In particular, the whole *rest* of the code in that

        if (!netif_carrier_ok(dev->net)) {

no longer makes sense after we've turned the link on with that

                if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
                        netif_carrier_on(dev->net);

sequence.

Put another way - once we've turned the carrier on, now that whole

                /* 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
                 */

thing makes no sense.

So my gut feel is that the

                if (test_and_clear_bit(EVENT_LINK_CARRIER_ON, &dev->flags))
                        netif_carrier_on(dev->net);

should actually be done outside that if-statement entirely, because it
literally ends up changing the thing that if-statement is testing.

And no, I didn't actually test that version, because I was hoping that
somebody who actually knows this code better would pipe up.

                Linus