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Message-ID: <20250805202848.GC61519@horms.kernel.org>
Date: Tue, 5 Aug 2025 21:28:48 +0100
From: Simon Horman <horms@...nel.org>
To: Ammar Faizi <ammarfaizi2@...weeb.org>
Cc: Oliver Neukum <oneukum@...e.com>, Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Linux Netdev Mailing List <netdev@...r.kernel.org>,
Linux USB Mailing List <linux-usb@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Armando Budianto <sprite@...weeb.org>, gwml@...r.gnuweeb.org,
stable@...r.kernel.org, John Ernberg <john.ernberg@...ia.se>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH net v2] net: usbnet: Fix the wrong netif_carrier_on()
call placement
+ 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:
> > 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 <sprite@...weeb.org>
> > Cc: stable@...r.kernel.org
> > 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@...weeb.org>
> > ---
> >
> > 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/
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@...nel.org>
> >
> > 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
> >
> >
>
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