On 12/20/2017 02:41 PM, Cong Wang wrote:
> On Wed, Dec 20, 2017 at 12:09 PM, John Fastabend
> <john.fastab...@gmail.com> wrote:
>> RCU grace period is needed for lockless qdiscs added in the commit
>> c5ad119fb6c09 ("net: sched: pfifo_fast use skb_array").
>>
>> It is needed now that qdiscs may be lockless otherwise we risk
>> free'ing a qdisc that is still in use from datapath. Additionally,
>> push list cleanup into RCU callback. Otherwise we risk the datapath
>> adding skbs during removal.
>
> What about qdisc_graft() -> dev_deactivate() -> synchronize_net() ?
> It doesn't work with your "lockless" patches?
>
Well this is only in the 'parent == NULL' case otherwise we call
cops->graft(). Most sch_* seem to use qdisc_replace and this uses
sch_tree_lock().
The only converted qdisc mq and mqprio at this point don't care
though and do their own dev_deactivate/activate. So its not fixing
anything in the above mentioned commit.
I still think it will need to be done eventually. If it resolves
the miniq case it seems like a good idea. Although per Jakub's comment
perhaps I pulled too much into the RCU handler.
