linux-kernel - Re: [PATCH net v3] net: usb: Remove disruptive netif_wake_queue in rtl8150_set

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Message-ID: <20250924135814.GC5387@cabron.k.g>
Date: Wed, 24 Sep 2025 16:58:14 +0300
From: Petko Manolov <petkan@...leusys.com>
To: I Viswanath <viswanathiyyappan@...il.com>
Cc: kuba@...nel.org, michal.pecio@...il.com, edumazet@...gle.com,
	andrew+netdev@...n.ch, davem@...emloft.net, pabeni@...hat.com,
	linux-usb@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev, david.hunter.linux@...il.com,
	syzbot+78cae3f37c62ad092caa@...kaller.appspotmail.com
Subject: Re: [PATCH net v3] net: usb: Remove disruptive netif_wake_queue in
 rtl8150_set_multicast

On 25-09-24 19:13:50, I Viswanath wrote:
> syzbot reported WARNING in rtl8150_start_xmit/usb_submit_urb.
> This is the sequence of events that leads to the warning:
> 
> rtl8150_start_xmit() {
> 	netif_stop_queue();
> 	usb_submit_urb(dev->tx_urb);
> }
> 
> rtl8150_set_multicast() {
> 	netif_stop_queue();
> 	netif_wake_queue();		<-- wakes up TX queue before URB is done
> }
> 
> rtl8150_start_xmit() {
> 	netif_stop_queue();
> 	usb_submit_urb(dev->tx_urb);	<-- double submission
> }
> 
> rtl8150_set_multicast being the ndo_set_rx_mode callback should not be calling
> netif_stop_queue and notif_start_queue as these handle TX queue
> synchronization.

netif_[stop|wake]_queue() should have been removed from rtl8150_set_multicast()
long time ago, but somehow it has slipped under the radar.  As far as i can tell
this is the only change needed.


		Petko


> The net core function dev_set_rx_mode handles the synchronization
> for rtl8150_set_multicast making it safe to remove these locks.
> 
> Reported-and-tested-by: syzbot+78cae3f37c62ad092caa@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=78cae3f37c62ad092caa
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Tested-by: Michal Pecio <michal.pecio@...il.com>
> Signed-off-by: I Viswanath <viswanathiyyappan@...il.com>
> ---
> v1: 
> Link: https://lore.kernel.org/netdev/20250920045059.48400-1-viswanathiyyappan@gmail.com/
>  
> v2:
> - Add explanation why netif_stop_queue/netif_wake_queue can be safely removed
> - Add the net prefix to the patch, designating it to the net tree
> Link: https://lore.kernel.org/netdev/20250920181852.18164-1-viswanathiyyappan@gmail.com/
>  
> v3:
> - Simplified the event sequence that lead to the warning
> - Added Tested-by tag
> 
>  drivers/net/usb/rtl8150.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
> index ddff6f19ff98..92add3daadbb 100644
> --- a/drivers/net/usb/rtl8150.c
> +++ b/drivers/net/usb/rtl8150.c
> @@ -664,7 +664,6 @@ static void rtl8150_set_multicast(struct net_device *netdev)
>  	rtl8150_t *dev = netdev_priv(netdev);
>  	u16 rx_creg = 0x9e;
>  
> -	netif_stop_queue(netdev);
>  	if (netdev->flags & IFF_PROMISC) {
>  		rx_creg |= 0x0001;
>  		dev_info(&netdev->dev, "%s: promiscuous mode\n", netdev->name);
> @@ -678,7 +677,6 @@ static void rtl8150_set_multicast(struct net_device *netdev)
>  		rx_creg &= 0x00fc;
>  	}
>  	async_set_registers(dev, RCR, sizeof(rx_creg), rx_creg);
> -	netif_wake_queue(netdev);
>  }
>  
>  static netdev_tx_t rtl8150_start_xmit(struct sk_buff *skb,
> -- 
> 2.47.3
>