Re: [PATCH net] net: bcmasp: fix lost TX wakeup race with lockless queue API

[Justin Chen <justin.chen@broadcom.com>]

On 9/28/26 2:35 PM, Nicolai Buchwitz wrote:
> Hi Justin
> 
> On 28.9.2026 22:18, justin.chen@broadcom.com wrote:
>> From: Justin Chen <justin.chen@broadcom.com>
>>
>> netif_stop_queue() in bcmasp_xmit() raced with netif_wake_queue() in
>> bcmasp_tx_poll(): a reclaim landing between the ring-full check and
>> the stop call left the queue stopped despite free descriptors,
>> hanging TX until timeout.
>>
>> Switch to netif_txq_maybe_stop()/netif_txq_completed_wake() (the
>> lockless TX queue API, which also brings in BQL), replace
>> tx_spb_ring_full() with a live bcmasp_tx_avail() count.
>>
>> Fixes: 490cb412007d ("net: bcmasp: Add support for ASP2.0 Ethernet 
>> controller")
>> Signed-off-by: Justin Chen <justin.chen@broadcom.com>
>> Assisted-by: Claude:claude-sonnet-5
>> ---
>>  .../net/ethernet/broadcom/asp2/bcmasp_intf.c  | 68 +++++++++++--------
> 
>> [...]
> 
>>  static struct sk_buff *bcmasp_csum_offload(struct net_device *dev,
>> @@ -241,16 +239,18 @@ static netdev_tx_t bcmasp_xmit(struct sk_buff 
>> *skb, struct net_device *dev)
>>      struct bcmasp_tx_cb *txcb;
>>      dma_addr_t mapping, valid;
>>      struct bcmasp_desc *desc;
>> +    struct netdev_queue *txq;
>>      bool csum_hw = false;
>>      struct device *kdev;
>>      skb_frag_t *frag;
>>
>>      kdev = &intf->parent->pdev->dev;
>> +    txq = netdev_get_tx_queue(dev, 0);
>>
>>      nr_frags = skb_shinfo(skb)->nr_frags;
>>
>> -    if (tx_spb_ring_full(intf, nr_frags + 1)) {
>> -        netif_stop_queue(dev);
>> +    if (unlikely(bcmasp_tx_avail(intf) < nr_frags + 1)) {
>> +        netif_tx_stop_queue(txq);
> 
> nit: AFAIU this is unreachable for now, but to prevent future races maybe
> better use netif_txq_try_stop()?

Will use netif_txq_try_stop() in v2. My understanding is this is still 
reachable since the maybe_stop call at the end of the xmit may have 
false wake ups when the ring is full. That is what is documented in the 
function header description for netif_txq_try_stop().

Thanks,
Justin
> 
>> [...]
> 
> Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
> 
> Thanks,
> Nicolai