[PATCH net] net: stmmac: Complete meta data only when enabled

[Maciej Fijalkowski]

On Thu, Feb 22, 2024 at 11:53:14AM -0800, Stanislav Fomichev wrote:
> On Thu, Feb 22, 2024 at 1:45 AM Kurt Kanzenbach <kurt at linutronix.de> wrote:
> >
> > Currently using XDP/ZC sockets on stmmac results in a kernel crash:
> >
> > |[  255.822584] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

would be good to explain where it comes from, no?

xsk_tx_metadata_to_compl() works on meta == NULL, it does not set
compl->tx_timestamp and later on xsk_tx_metadata_complete() tries to
dereference that.

> > |[...]
> > |[  255.822764] Call trace:
> > |[  255.822766]  stmmac_tx_clean.constprop.0+0x848/0xc38
> >
> > The program counter indicates xsk_tx_metadata_complete(). However, this
> > function shouldn't be called unless metadata is actually enabled.
> >
> > Tested on imx93 without XDP, with XDP and with XDP/ZC.
> >
> > Fixes: 1347b419318d ("net: stmmac: Add Tx HWTS support to XDP ZC")
> > Suggested-by: Serge Semin <fancer.lancer at gmail.com>
> > Signed-off-by: Kurt Kanzenbach <kurt at linutronix.de>
> > Tested-by: Serge Semin <fancer.lancer at gmail.com>
> > Link: https://lore.kernel.org/netdev/87r0h7wg8u.fsf@kurt.kurt.home/
> 
> Acked-by: Stanislav Fomichev <sdf at google.com>
> 
> LGTM, thanks!
> 
> > ---
> >  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index e80d77bd9f1f..8b77c0952071 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -2672,7 +2672,8 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue,
> >                         }
> >                         if (skb) {
> >                                 stmmac_get_tx_hwtstamp(priv, p, skb);
> > -                       } else {
> > +                       } else if (tx_q->xsk_pool &&
> > +                                  xp_tx_metadata_enabled(tx_q->xsk_pool)) {
> >                                 struct stmmac_xsk_tx_complete tx_compl = {
> >                                         .priv = priv,
> >                                         .desc = p,
> >
> > ---
> > base-commit: 603ead96582d85903baec2d55f021b8dac5c25d2
> > change-id: 20240222-stmmac_xdp-585ebf1680b3
> >
> > Best regards,
> > --
> > Kurt Kanzenbach <kurt at linutronix.de>
> >