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From:   Shenwei Wang <shenwei.wang@nxp.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
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Subject: RE: [EXT] Re: [PATCH v2 1/1] net: fec: add initial XDP support
Thread-Topic: [EXT] Re: [PATCH v2 1/1] net: fec: add initial XDP support
Thread-Index: AQHY7UT3Rg7ikccfbkSHV941HzNcma4ovLaAgAAVGBA=
Date:   Mon, 31 Oct 2022 18:34:02 +0000
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 <Y2ABb+G+ykcUd413@lunn.ch>
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Monday, October 31, 2022 12:10 PM
> To: Shenwei Wang <shenwei.wang@nxp.com>
> > +                     cbd_base =3D rxq->bd.base;
> > +                     if (bpf->prog)
> > +                             rxq->bd.ring_size =3D XDP_RX_RING_SIZE;
> > +                     else
> > +                             rxq->bd.ring_size =3D RX_RING_SIZE;
> > +                     size =3D dsize * rxq->bd.ring_size;
> > +                     cbd_base =3D (struct bufdesc *)(((void *)cbd_base=
) + size);
> > +                     rxq->bd.last =3D (struct bufdesc *)(((void
> > + *)cbd_base) - dsize);
>=20
> This does not look safe. netif_tx_disable(dev) will stop new transmission=
s, but
> the hardware can be busy receiving, DMAing frames, using the descriptors,=
 etc.
> Modifying rxq->bd.last in particular seems risky. I think you need to dis=
able the
> receiver, wait for it to indicate it really has stopped, and only then ma=
ke these
> modifications.
>=20

Sounds reasonable. How about moving the codes of updating ring size to the =
place
right after the enet reset inside the fec_restart? This should clear those =
risky corner
cases.

Thanks,
Shenwei

>         Andrew