Re: [PATCH net v2 2/2] net: stmmac: Stop Tx queue when (en|dis)abling XSK pools

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Mon, Oct 05, 2026 at 09:09:33AM +0200, Kurt Kanzenbach wrote:
> When enabling or disabling XSK pools in parallel to Tx traffic, kernel
> crashes occur. For VLAN tagged frames that happens in stmmac_xmit() ->
> dwmac4_set_vlan_tag() and for normal frames in stmmac_xmit() ->
> dwmac4_set_addr(). Both of these functions access the Tx DMA descriptors.
> 
> The XDP pool (en|dis)ablement frees and reallocates the Tx DMA resources:
> 
>  stmmac_disable_tx_queue:
>    __free_dma_tx_desc_resources
> 
>  stmmac_enable_tx_queue:
>    __alloc_dma_tx_desc_resources
>    __init_dma_tx_desc_rings
> 
> NAPI is disabled during that allocation window, but the Tx queue is not
> stopped. Therefore, add the stopping of the Tx queue during the enabling
> and disabling of XSK pools. Update trans_start when stopping the queue
> to avoid spurious watchdog timeouts.
> 
> The issue can be easily reproduced by:
> 
>  1. Run iperf
>  2. Run application which opens an AF_XDP/ZC socket
> 
> Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket")
> Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> index d7e4db7224b0..883bd3fe8089 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_xdp.c
> @@ -6,6 +6,16 @@
>  #include "stmmac.h"
>  #include "stmmac_xdp.h"
>  
> +static void stmmac_xdp_stop_tx_queue(struct stmmac_priv *priv, u16 queue)
> +{
> +	struct netdev_queue *nq = netdev_get_tx_queue(priv->dev, queue);
> +
> +	__netif_tx_lock_bh(nq);
> +	txq_trans_cond_update(nq);
> +	netif_tx_stop_queue(nq);
> +	__netif_tx_unlock_bh(nq);
> +}
> +
>  static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  				  struct xsk_buff_pool *pool, u16 queue)
>  {
> @@ -36,6 +46,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  	if (need_update) {
>  		napi_disable(&ch->rx_napi);
>  		napi_disable(&ch->tx_napi);
> +		stmmac_xdp_stop_tx_queue(priv, queue);

FWIW you can look at what I did at ice driver (ice_qp_dis()) where I used
a bigger hammer here; I think updating trans_start is kinda a workaround.

https://lore.kernel.org/netdev/20240708221416.625850-1-anthony.l.nguyen@intel.com/

>  		stmmac_disable_rx_queue(priv, queue);
>  		stmmac_disable_tx_queue(priv, queue);
>  	}
> @@ -46,6 +57,7 @@ static int stmmac_xdp_enable_pool(struct stmmac_priv *priv,
>  		stmmac_enable_rx_queue(priv, queue);
>  		stmmac_enable_tx_queue(priv, queue);
>  		napi_enable(&ch->rxtx_napi);
> +		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
>  
>  		err = stmmac_xsk_wakeup(priv->dev, queue, XDP_WAKEUP_RX);
>  		if (err)
> @@ -73,6 +85,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
>  
>  	if (need_update) {
>  		napi_disable(&ch->rxtx_napi);
> +		stmmac_xdp_stop_tx_queue(priv, queue);
>  		stmmac_disable_rx_queue(priv, queue);
>  		stmmac_disable_tx_queue(priv, queue);
>  		synchronize_rcu();
> @@ -87,6 +100,7 @@ static int stmmac_xdp_disable_pool(struct stmmac_priv *priv, u16 queue)
>  		stmmac_enable_tx_queue(priv, queue);
>  		napi_enable(&ch->rx_napi);
>  		napi_enable(&ch->tx_napi);
> +		netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, queue));
>  	}
>  
>  	return 0;
> 
> -- 
> 2.47.3
> 
>