linux-kernel - Re: [PATCH net v2] net: usbnet: Fix the wrong netif_carrier

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Message-ID: <20250804100050.GQ8494@horms.kernel.org>
Date: Mon, 4 Aug 2025 11:00:50 +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>
Subject: Re: [PATCH net v2] net: usbnet: Fix the wrong netif_carrier_on()
 call placement

+ 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(-)
> 
> 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
> 
>