Re: net: r8169: a question of memory barrier in the r8169 driver

[Jia-Ju Bai]

On 2018/1/19 9:11, Francois Romieu wrote:
> Jia-Ju Bai <baijiaju1990@xxxxxxxxx> :
> [...]
> > The function rtl8169_start_xmit reads tp->dirty_tx in TX_FRAGS_READY_FOR:
> >      if (unlikely(!TX_FRAGS_READY_FOR(tp, skb_shinfo(skb)->nr_frags))) {
> >          netif_err(tp, drv, dev, "BUG! Tx Ring full when queue awake!\n");
> >          goto err_stop_0;
> >      }
> > But there is no memory barrier around this code.
> >
> > Is there a possible data race here?
> This code would not even be needed if rtl8169_start_xmit was only your
> usual ndo_start_xmit handler: Realtek {ab / re}used it for GSO handling
> (see r8169_csum_workaround).
>
> If the test is not a no-op in this GSO context, it's racy.

Thanks for reply.
I didn't clearly understand your meaning...
I wonder whether there is a possible data race and whether a "smp_mb" is 
needed before this code?
By the way, do you mean that this code can be removed?


Thanks,
Jia-Ju Bai