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

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Date:   Tue, 24 Sep 2019 16:47:59 -0700
From:   Grant Grundler <grundler@...omium.org>
To:     Hayes Wang <hayeswang@...ltek.com>
Cc:     Prashant Malani <pmalani@...omium.org>,
        "grundler@...omium.org" <grundler@...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 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"?

> 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
>