Re: [PATCH net v2] net: sched: do not requeue a NULL skb

[Cong Wang]

On Mon, Apr 11, 2016 at 8:52 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> On Mon, 2016-04-11 at 17:17 +0200, Lars Persson wrote:
>>
>> On 04/11/2016 04:22 PM, Eric Dumazet wrote:
>> > On Mon, 2016-04-11 at 15:38 +0200, Lars Persson wrote:
>> >
>> >> I though it would be prudent because the queue can be non-empty even for
>> >> the case of skb=NULL. So should it be there in this patch, another patch
>> >> or not at all ?
>> >
>> > Then maybe change return code ?
>> >
>> > It seems strange that a validate_xmit_skb_list() failure stops the
>> > __qdisc_run() loop but schedules another round.
>> >
>> >
>>
>> It was suggested by Cong Wang to return 0 in order to stop the loop. Do
>> you guys agree that the loop should be stopped for such failures ? Then
>> I will put the schedule call inside the if as you proposed earlier.
>
> What are the causes of validate_xmit_skb_list() failures ?
>
> If gso segmentations fail because of memory pressure, better free more
> skbs right now.
>
> In any case, having a single test " if (skb)  " sounds better to me,
> to have a fast path.
>
> So your first patch was probably a better idea.
>
> v2 has two tests instead of one.

I am fine with either way as long as the loop stops on failure.
Folding the test "if (skb)" into one also requires to retake the spinlock.