Re: [PATCH net] net: ethernet: ti: am65-cpsw: Fix NAPI registration sequence

[Sverdlin, Alexander]

Hi Siddharth!

On Tue, 2025-03-11 at 11:42 +0530, Siddharth Vadapalli wrote:
> From: Vignesh Raghavendra <vigneshr@xxxxxx>
> 
> Registering the interrupts for TX or RX DMA Channels prior to registering
> their respective NAPI callbacks can result in a NULL pointer dereference.
> This is seen in practice as a random occurrence since it depends on the
> randomness associated with the generation of traffic by Linux and the
> reception of traffic from the wire.
> 
> Fixes: 681eb2beb3ef ("net: ethernet: ti: am65-cpsw: ensure proper channel cleanup in error path")

The patch Vignesh mentions here...

> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
> Co-developed-by: Siddharth Vadapalli <s-vadapalli@xxxxxx>
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@xxxxxx>
> ---
> 
> Hello,
> 
> This patch is based on commit
> 4d872d51bc9d Merge tag 'x86-urgent-2025-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> of Mainline Linux.
> 
> Regards,
> Siddharth.
> 
>  drivers/net/ethernet/ti/am65-cpsw-nuss.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> index 2806238629f8..d5291281c781 100644
> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> @@ -2314,6 +2314,9 @@ static int am65_cpsw_nuss_ndev_add_tx_napi(struct am65_cpsw_common *common)
>  		hrtimer_init(&tx_chn->tx_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
>  		tx_chn->tx_hrtimer.function = &am65_cpsw_nuss_tx_timer_callback;
>  
> +		netif_napi_add_tx(common->dma_ndev, &tx_chn->napi_tx,
> +				  am65_cpsw_nuss_tx_poll);
> +
>  		ret = devm_request_irq(dev, tx_chn->irq,
>  				       am65_cpsw_nuss_tx_irq,
>  				       IRQF_TRIGGER_HIGH,
> @@ -2323,9 +2326,6 @@ static int am65_cpsw_nuss_ndev_add_tx_napi(struct am65_cpsw_common *common)
>  				tx_chn->id, tx_chn->irq, ret);
>  			goto err;
>  		}
> -
> -		netif_napi_add_tx(common->dma_ndev, &tx_chn->napi_tx,
> -				  am65_cpsw_nuss_tx_poll);

... has accounted for the fact ..._napi_add_... happens after [possibly unsuccessful] request_irq,
please grep for "for (--i ;". Is it necessary to adjust both loops, in the below case too?

>  	}
>  
>  	return 0;
> @@ -2569,6 +2569,9 @@ static int am65_cpsw_nuss_init_rx_chns(struct am65_cpsw_common *common)
>  			     HRTIMER_MODE_REL_PINNED);
>  		flow->rx_hrtimer.function = &am65_cpsw_nuss_rx_timer_callback;
>  
> +		netif_napi_add(common->dma_ndev, &flow->napi_rx,
> +			       am65_cpsw_nuss_rx_poll);
> +
>  		ret = devm_request_irq(dev, flow->irq,
>  				       am65_cpsw_nuss_rx_irq,
>  				       IRQF_TRIGGER_HIGH,
> @@ -2579,9 +2582,6 @@ static int am65_cpsw_nuss_init_rx_chns(struct am65_cpsw_common *common)
>  			flow->irq = -EINVAL;
>  			goto err_flow;
>  		}
> -
> -		netif_napi_add(common->dma_ndev, &flow->napi_rx,
> -			       am65_cpsw_nuss_rx_poll);
>  	}
>  
>  	/* setup classifier to route priorities to flows */

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com