netdev - Re: [PATCH net] net: stmmac: fix the crash issue for zero copy XDP

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Message-ID: <aUUjJH1tQkN1UcYL@test-OptiPlex-Tower-Plus-7010>
Date: Fri, 19 Dec 2025 15:34:20 +0530
From: Hariprasad Kelam <hkelam@...vell.com>
To: Wei Fang <wei.fang@....com>
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Subject: Re: [PATCH net] net: stmmac: fix the crash issue for zero copy
 XDP_TX action

On 2025-12-18 at 12:06:47, Wei Fang (wei.fang@....com) wrote:
> > On 2025-12-17 at 18:19:19, Wei Fang (wei.fang@....com) wrote:
> > > > > -	res = stmmac_xdp_xmit_xdpf(priv, queue, xdpf, false);
> > > > > -	if (res == STMMAC_XDP_TX)
> > > > > +	/* For zero copy XDP_TX action, dma_map is true */
> > > > > +	res = stmmac_xdp_xmit_xdpf(priv, queue, xdpf, zc);
> > > > 	Seems stmmac_xdp_xmit_xdpf is using dma_map_single if we pass zc is
> > > > true.
> > > >         Ideally in case of zc, driver can use
> > > > page_pool_get_dma_addr, may be you
> > > >         need pass zc param as false. Please check
> > > >
> > >
> > > No, the memory type of xdpf->data is MEM_TYPE_PAGE_ORDER0 rather than
> > > MEM_TYPE_PAGE_POOL, so we should use dma_map_single().
> > > Otherwise, it will lead to invalid mappings and cause the crash.
> > >
> > >
> >  ACK, found below code bit confusing
> > 		case STMMAC_XDP_CONSUMED:
> >  			xsk_buff_free(buf->xdp);
> > +			fallthrough;
> > +		case STMMAC_XSK_CONSUMED:
> >  			rx_dropped++;
> > 
> >      Ideally in case of STMMAC_XSK_CONSUMED, driver needs to call
> > xsk_buff_free.
> >      And in case of STMMAC_XDP_CONSUMED, driver needs to call
> > xdp_return_frame.
> >      May be you can move all buffer free logic to stmmac_rx_zc with above
> > suggested
> >      changes.
> 
> For zero copy, the xdp_buff is freed by xdp_convert_buff_to_frame()
> when converting the xdp_xdp to xdp_frame. So STMMAC_XSK_CONSUMED
> means the xdp_buff has been freed, it tells stmmac_rx_zc() no to free a
> xdp_buff that has been freed.
> 
> I have added a comment for STMMAC_XSK_CONSUMED, see
> 
> +       } else if (res == STMMAC_XDP_CONSUMED && zc) {
> +               /* xdp has been freed by xdp_convert_buff_to_frame(),
> +                * no need to call xsk_buff_free() again, so return
> +                * STMMAC_XSK_CONSUMED.
> +                */
> +               res = STMMAC_XSK_CONSUMED;
> +               xdp_return_frame(xdpf);
> +       }
> 
>
 ACK. 
Reviewed-by: Hariprasad Kelam <hkelam@...vell.com>