Re: [PATCH] net: usb: kaweth: remove TX queue manipulation in kaweth_set_rx_mode

[Paolo Abeni <pabeni@redhat.com>]

On 2/9/26 6:48 PM, Ziyi Guo wrote:
> On Mon, Feb 9, 2026 at 7:56 AM Andrew Lunn <andrew@lunn.ch> wrote:
>>
>> I think there needs to be a better explanation why it is safe to
>> remove these stop and wake queue operations. r8152 does the same. Is
>> it also broken? Rather than removing these, should we actually be
>> waiting for the completion of the urb?
>>
>>         Andrew
> 
> Hi Andrew,
> 
> Thank you for your time and email, here is my understanding (correct
> me if I'm wrong).
> 
> I think ndo_set_rx_mode runs in atomic context with a spinlock held,
> if we wait for the completion, this would sleep under a spinlock.
> 
> And it seems the architecture of r8152 is different from kaweth and
> rtl8150. In r8152, the ndo_set_rx_mode callback (rtl8152_set_rx_mode)
> won't directly call netif_stop_queue/netif_wake_queue. It only sets a
> flag and schedules delayed work.
> The function that does call netif_stop_queue/netif_wake_queue is
> _rtl8152_set_rx_mode(), which runs from the work handler
> rtl_work_func_t() under tp->control mutex, not from the ndo callback
> under netif_addr_lock_bh.
> Also, r8152's start_xmit never submits URBs directly. It only queues
> SKBs to a software queue. Actual URB submission happens in a separate
> tasklet using a pool of 4 independent TX aggregation buffers, each
> with its own URB.
> 
> So even if netif_wake_queue() triggers start_xmit, it just adds an SKB
> to the software queue, no URB is touched, and no double-submission can
> occur.
> 
> In kaweth and rtl8150, start_xmit calls usb_submit_urb() directly on a
> single shared tx_urb, so the netif_wake_queue() from the ndo callback
> causes the stack to call start_xmit while that URB is still in-flight.

It looks like kaweth_set_rx_mode() is already functionally broken: the
real set_rx_mode action is performed by kaweth_async_set_rx_mode, which
in turn is not a no-op only at ndo_open() time.

So this looks safe to me.

/P