[Cake] lockup with multiple cake instances on 3.16.7

[Pete Heist]

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? It can be reproduced as follows:

-----
# Either htb of hfsc can be used, but it doesn’t happen with fq_codel or sfq.
# Also, when magic number “5” below is changed to “4”, no lockup occurs.
tc qdisc add dev eth0 root handle 1: htb default 1
for i in {1..5}; do
    tc class add dev eth0 parent 1: classid 1:$i htb rate 100mbit ceil 100mbit
    tc qdisc add dev eth0 parent 1:$i cake
done

# lockup occurs on execution of this command
tc qdisc show dev eth0
-----

When the lockup occurs, all network activity stops and the serial console freezes. Eventually the machine either reboots itself or needs to be power cycled. I caught the attached output to the console. I do not see it on kernel 3.10.107 with mipsle, or any other later kernels that I have, which are all 4.x and later.

Otherwise, it looks like we’ll have to upgrade these older kernels at FreeNet to use cake… :)

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: cake_lockup.txt
URL: <https://lists.bufferbloat.net/pipermail/cake/attachments/20190130/490c2f2b/attachment.txt>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: cake_lockup2.txt
URL: <https://lists.bufferbloat.net/pipermail/cake/attachments/20190130/490c2f2b/attachment-0001.txt>