netdev - Re: [PATCH 2/2] net: sched: convert qdisc linked list to hashtable

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Date:	Fri, 12 Aug 2016 16:44:32 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Jiri Kosina <jikos@...nel.org>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Phil Sutter <phil@....cc>,
	Cong Wang <xiyou.wangcong@...il.com>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: sched: convert qdisc linked list to hashtable

On 08/12/2016 04:36 PM, Jiri Kosina wrote:
> On Fri, 12 Aug 2016, Daniel Borkmann wrote:
>
>>> I was thinking about something like the patch below (the reasong being
>>> that ->dev would be NULL only in cases of singletonish qdiscs) ...
>>> wouldn't that also fix the issue you're seeing? Have to think it
>>> through a little bit more ..
>>
>> Ahh, so this has the same effect as previously observed with the other fix.
>
> Thanks a lot for confirming that this fixes the panic. I still have to
> think a little bit more about this though.
>
>> Perhaps it's just a dumping issue, but to the below clsact, there shouldn't
>> be pfifo_fast instances appearing.
>>
>> # tc qdisc show dev wlp2s0b1
>> qdisc mq 0: root
>> qdisc pfifo_fast 0: parent :4 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :3 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :2 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :1 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> # tc qdisc add dev wlp2s0b1 clsact
>> # tc qdisc show dev wlp2s0b1
>> qdisc mq 0: root
>> qdisc pfifo_fast 0: parent :4 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :3 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :2 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :1 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc clsact ffff: parent ffff:fff1
>> qdisc pfifo_fast 0: parent :4 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :3 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :2 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>> qdisc pfifo_fast 0: parent :1 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>
> Hmm, no immediate idea where those are coming from, we'll have to figure
> it out. The mq device used here has 4 queues, right?

Yes, the first tc qdisc show is after boot and how it should normally
look like, so 4 tx queues.

# ls /sys/class/net/wlp2s0b1/queues/
rx-0  tx-0  tx-1  tx-2  tx-3

When adding clsact, only the 'qdisc clsact' line should be extra. Given
the extra pfifo_fast ones look the same as above, I would suspect a htab
dumping issue, perhaps. I can debug a bit later tonight on this.