linux-kernel - RE: [PATCH net] net: xilinx: axienet: Increment Rx skb ring head pointer after BD is successfully allocated in dmaengine flow

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Message-ID:
 <MN0PR12MB5953E5B18BAC06C0116B0F7FB72DA@MN0PR12MB5953.namprd12.prod.outlook.com>
Date: Wed, 6 Aug 2025 09:03:16 +0000
From: "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
To: "Gupta, Suraj" <Suraj.Gupta2@....com>, "andrew+netdev@...n.ch"
	<andrew+netdev@...n.ch>, "davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "kuba@...nel.org"
	<kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>, "Simek, Michal"
	<michal.simek@....com>, "sean.anderson@...ux.dev" <sean.anderson@...ux.dev>,
	"horms@...nel.org" <horms@...nel.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Katakam, Harini" <harini.katakam@....com>
Subject: RE: [PATCH net] net: xilinx: axienet: Increment Rx skb ring head
 pointer after BD is successfully allocated in dmaengine flow

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Suraj Gupta <suraj.gupta2@....com>
> Sent: Wednesday, August 6, 2025 12:50 AM
> To: andrew+netdev@...n.ch; davem@...emloft.net; edumazet@...gle.com;
> kuba@...nel.org; pabeni@...hat.com; Simek, Michal <michal.simek@....com>;
> sean.anderson@...ux.dev; Pandey, Radhey Shyam
> <radhey.shyam.pandey@....com>; horms@...nel.org
> Cc: netdev@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; Katakam, Harini <harini.katakam@....com>
> Subject: [PATCH net] net: xilinx: axienet: Increment Rx skb ring head pointer after
> BD is successfully allocated in dmaengine flow
>
> In DMAengine flow, AXI DMA driver invokes callback before freeing BD in
> irq handling path.
> In Rx callback (axienet_dma_rx_cb()), axienet driver tries to allocate
> new BD after processing skb.
> This will be problematic if both AXI-DMA and AXI ethernet have same
> BD count as all Rx BDs will be allocated initially and it won't be
> able to allocate new one after Rx irq. Incrementing head pointer w/o
> checking for BD allocation will result in garbage values in skb BD and
> cause the below kernel crash:
>
> Unable to handle kernel paging request at virtual address fffffffffffffffa
> <snip>
> Internal error: Oops: 0000000096000006 [#1]  SMP
> pc : axienet_dma_rx_cb+0x78/0x150
> lr : axienet_dma_rx_cb+0x78/0x150
>  Call trace:
>   axienet_dma_rx_cb+0x78/0x150 (P)
>   xilinx_dma_do_tasklet+0xdc/0x290
>   tasklet_action_common+0x12c/0x178
>   tasklet_action+0x30/0x3c
>   handle_softirqs+0xf8/0x230
> <snip>
>
> Fixes: 6a91b846af85 ("net: axienet: Introduce dmaengine support")
> Signed-off-by: Suraj Gupta <suraj.gupta2@....com>

Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@....com>

> ---
>  drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 6011d7eae0c7..acd5be60afec 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -1457,7 +1457,6 @@ static void axienet_rx_submit_desc(struct net_device
> *ndev)
>       if (!skbuf_dma)
>               return;
>
> -     lp->rx_ring_head++;
>       skb = netdev_alloc_skb(ndev, lp->max_frm_size);
>       if (!skb)
>               return;
> @@ -1482,6 +1481,7 @@ static void axienet_rx_submit_desc(struct net_device
> *ndev)
>       skbuf_dma->desc = dma_rx_desc;
>       dma_rx_desc->callback_param = lp;
>       dma_rx_desc->callback_result = axienet_dma_rx_cb;
> +     lp->rx_ring_head++;
>       dmaengine_submit(dma_rx_desc);
>
>       return;
> --
> 2.25.1