On Fri, Jul 17, 2015 at 5:27 PM, Alex Gartrell <alexgartr...@gmail.com> wrote:
> On Fri, Jul 17, 2015 at 5:10 PM, Cong Wang <cw...@twopensource.com> wrote:
>> Hmm, but in htb_delete() we do reset the leaf qdisc before removing the
>> class from ha
>>
>> if (!cl->level) {
>> qlen = cl->un.leaf.q->q.qlen;
>> qdisc_reset(cl->un.leaf.q);
>> qdisc_tree_decrease_qlen(cl->un.leaf.q, qlen);
>> }
>>
>> therefore, the leaf fq_codel qdisc is supposed to have 0 skb after that,
>> that is, the second fq_codel_reset() is supposed to return NULL immediately?
>> Why is qdidsc_tree_decrease_qlen() called in the second fq_codel_reset()?
>>
>> Or there is a race condition between ->delete() and ->put()? In which new
>> skb can be enqueued?
>
> This makes the most sense to me, but I have ~32 hours of experience
> with this subsystem :)
>
> Taking that for granted, it seems like it'd be appropriate to note the
> invariant in the code i've changed with a WARN_ON and to skip it, and
> then to otherwise find a way to close the hole. Do you agree?
>
Your patch _does_ make sense for me, I was just trying to check
if there is any better way to fix it. :)
I was thinking about locking the qdisc tree before ->get(), but it is not
easy and may not worth the effort either. So, unless others have a
better idea here, I think your patch is fine, just please update the
changelog and rebase it against latest -net tree.
Thanks!
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