[Cake] lockup with multiple cake instances on 3.16.7

[Pete Heist]

Thanks much for the try, only that didn’t fix it yet. I also tried changing two more calls to sch_tree_lock/unlock in cake_change to the maybe versions (recognizing that those may have still been there on purpose), but I still see the lockup. Even commented all the lock calls out to make sure.

I noticed that tc-adv is without xtables support when I compile it (TC_CONFIG_NO_XT:=y) in case that makes any difference. No libxtables-dev package available on this distro.

Pete

> On Jan 30, 2019, at 11:59 PM, Toke Høiland-Jørgensen <toke at redhat.com> wrote:
> 
> Pete Heist <pete at heistp.net> writes:
> 
>> I’m seeing a lockup with cake on 3.16.7 with 64-bit Intel when adding
>> more than 4 cake instances. I’m using cake and tc-adv from head. Does
>> anyone have an idea what this could be?
> 
> Looks like it's a compatibility issue with old kernels. Could you please
> check if the latest commit in the github repo fixes this? :)
> 
> The explanation, copied from that commit:
> 
>> The qdisc stats dumping was changed in 4.8 (by commit
>> edb09eb17ed89eaa82a52dd306beac93e292b485) to be lockless and moving the
>> responsibility for taking the qdisc root lock into the qdisc itself. Cake
>> inherited this from FQ-CoDel, but it leads to deadlocks on old kernels
>> where the core stats dumping code still takes the root qdisc lock.
> 
> 
> -Toke