netdev - Re: [PATCH] r8152: Use guard clause and fix comment typos

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Date:   Tue, 24 Sep 2019 17:28:01 -0700
From:   Grant Grundler <grundler@...omium.org>
To:     Grant Grundler <grundler@...omium.org>
Cc:     Hayes Wang <hayeswang@...ltek.com>,
        Prashant Malani <pmalani@...omium.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>
Subject: Re: [PATCH] r8152: Use guard clause and fix comment typos

On Tue, Sep 24, 2019 at 4:47 PM Grant Grundler <grundler@...omium.org> wrote:
>
> On Mon, Sep 23, 2019 at 7:47 PM Hayes Wang <hayeswang@...ltek.com> wrote:
> >
> > Prashant Malani [mailto:pmalani@...omium.org]
> > > Sent: Tuesday, September 24, 2019 6:27 AM
> > > To: Hayes Wang
> > [...]
> > > -     do {
> > > +     while (1) {
> > >               struct tx_agg *agg;
> > > +             struct net_device *netdev = tp->netdev;
> > >
> > >               if (skb_queue_empty(&tp->tx_queue))
> > >                       break;
> > > @@ -2188,26 +2189,25 @@ static void tx_bottom(struct r8152 *tp)
> > >                       break;
> > >
> > >               res = r8152_tx_agg_fill(tp, agg);
> > > -             if (res) {
> > > -                     struct net_device *netdev = tp->netdev;
> > > +             if (!res)
> > > +                     break;
> >
> > I let the loop run continually until an error occurs or the queue is empty.
> > However, you stop the loop when r8152_tx_agg_fill() is successful.
>
> Hayes,
> Are you sure about both assertions?
> The do/while loop exits if "res == 0". Isn't that the same as "!res"?

Hayes,
Sorry, You are correct.

thanks,
grant

>
> > If an error occurs continually, the loop may not be broken.
>
> And what prevents that from happening with the current code?
>
> Should current code break out of the loop in -ENODEV case, right?
>
> That would be more obvious if the code inside the loop were:
>     ...
>     res = r8152_tx_agg_fill(tp, agg);
>     if (res == -ENODEV) {
>        ...
>        break;
>      }
>      if (!res)
>          break;
>     ...
>
> (Or whatever the right code is to "loop until an error occurs or queue
> is empty").
>
> cheers,
> grant
>
> >
> > > -                     if (res == -ENODEV) {
> > > -                             rtl_set_unplug(tp);
> > > -                             netif_device_detach(netdev);
> > > -                     } else {
> > > -                             struct net_device_stats *stats = &netdev->stats;
> > > -                             unsigned long flags;
> > > +             if (res == -ENODEV) {
> > > +                     rtl_set_unplug(tp);
> > > +                     netif_device_detach(netdev);
> > > +             } else {
> > > +                     struct net_device_stats *stats = &netdev->stats;
> > > +                     unsigned long flags;
> > >
> > > -                             netif_warn(tp, tx_err, netdev,
> > > -                                        "failed tx_urb %d\n", res);
> > > -                             stats->tx_dropped += agg->skb_num;
> > > +                     netif_warn(tp, tx_err, netdev,
> > > +                                "failed tx_urb %d\n", res);
> > > +                     stats->tx_dropped += agg->skb_num;
> > >
> > > -                             spin_lock_irqsave(&tp->tx_lock, flags);
> > > -                             list_add_tail(&agg->list, &tp->tx_free);
> > > -                             spin_unlock_irqrestore(&tp->tx_lock, flags);
> > > -                     }
> > > +                     spin_lock_irqsave(&tp->tx_lock, flags);
> > > +                     list_add_tail(&agg->list, &tp->tx_free);
> > > +                     spin_unlock_irqrestore(&tp->tx_lock, flags);
> > >               }
> > > -     } while (res == 0);
> > > +     }
> >
> > I think the behavior is different from the current one.
> >
> > Best Regards,
> > Hayes
> >