netdev - Re: [PATCH v2 2/3] net_sched: Add accessor function for packet length for qdiscs

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Message-ID: <20080726141844.GB2873@ami.dom.local>
Date:	Sat, 26 Jul 2008 16:18:44 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>, jussi.kivilinna@...et.fi,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/3] net_sched: Add accessor function for packet
	length for qdiscs

On Sat, Jul 26, 2008 at 03:21:42PM +0200, Patrick McHardy wrote:
> David Miller wrote:
>> From: Jarek Poplawski <jarkao2@...il.com>
>> Date: Fri, 25 Jul 2008 11:37:57 +0000
>>
>>> On Fri, Jul 25, 2008 at 03:57:12AM -0700, David Miller wrote:
>>>> Even TCP depends upon that NET_XMIT_* return value having some real
>>>> meaning, remember the HTB bug we tracked down last week? :-)
>>> Do you mean this bug you've forgotten to fix yet?
>>
>> I have not forgotten, it is in TODO list. :)
>>
>> I want to also inquire with Patrick about whether he is going to
>> perform the audit in this area which he said he wanted to do :-)
>
> I'm a bit backlogged, so it will take some more time.
>
>> Well, we have patch which fixes the problem for the tester, so we
>> could just merge that and at least have HTB fixed.  But we know there
>> are other instances of the same return value propagation problem and
>> Patrick's audit is sure to turn up other similar turds...

My proposal (as before) is to apply this patch now (it could hit more
people than we know), but I would do small changes yet:
- to do htb_activate() if (cl->un.leaf.q->q.qlen),
- to skip bstats.packets and .bytes updating for anything but
  NET_XMIT_SUCCESS,
so, both things just like in sch_hfsc.

> The other problem that affects all qdiscs supporting actions is
> TC_ACT_QUEUED/TC_ACT_STOLEN getting mapped to NET_XMIT_SUCCESS
> even though the packet is not queued, corrupting upper qdiscs'
> qlen counters.

Why can't we (temporarily) simply check such cl->un.leaf.q->q.qlen
before and after enqueing?

Jarek P.
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