Thanks for all your replies!
One thing I did notice in examining tc_ctl_tfilter was that there is
something like:
qdisc_lock_tree(dev);
tp->next = *back;
*back = tp;
qdisc_unlock_tree(dev);
And then proceed to the data structure down below with:
err = tp->ops->change(tp, cl, t->tcm_handle, tca, &fh);
Simply reordering these seems to ameliorate the problem greatly. I
don't know if this is a generic solution or something specific to the
basic filter only.
Chris Madden
jamal wrote:
> On Tue, 2007-20-03 at 08:29 +0100, Patrick McHardy wrote:
>
>> jamal wrote:
>>
>>> On Tue, 2007-20-03 at 07:58 +0100, Patrick McHardy wrote:
>>>
>>> Ok. It certainly used to matter in the old days.
>>>
>> Actually it has never been used anywhere else but in ing_filter,
>> it was introduced together with the TC actions.
>>
>>
>
> You are correct. I looked at old 2.4 and all i saw was:
>
> ----------
> /*
> revisit later: Use a private since lock dev->queue_lock is also
> used on the egress (might slow things for an iota)
> */
>
> if (dev->qdisc_ingress) {
> spin_lock(&dev->queue_lock);
> if ((q = dev->qdisc_ingress) != NULL)
> fwres = q->enqueue(skb, q);
> spin_unlock(&dev->queue_lock);
> }
> ------
>
> So the resolution (as Dave points out) was wrong. In any case, restoring
> queue_lock for now would slow things but will remove the race.
>
>
>> I'll try, but no promises, I'm a bit behind with various things myself.
>>
>
> I will ping you in a few days and if you havent done anything i will
> take it up.
> I am almost tempted to make the ingress filters to not have any
> dependencies on egress whatsoever. It will create more locks but
> will make the datapath faster. Actions can still be shared, but thats
> lesser of an overhead.
>
> cheers,
> jamal
>
>
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