netdev - Re: [Patch net-next 4/5] net_sched: forbid setting default qdisc to inappropriate ones

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Message-ID: <CAM_iQpWap83uA1CsR5rryLEoc4ffrJp3+=zPs+uAAhAtkKtG_w@mail.gmail.com>
Date:	Thu, 27 Aug 2015 18:49:09 -0700
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [Patch net-next 4/5] net_sched: forbid setting default qdisc to
 inappropriate ones

On Thu, Aug 27, 2015 at 4:18 PM, David Miller <davem@...emloft.net> wrote:
> From: Cong Wang <xiyou.wangcong@...il.com>
> Date: Thu, 27 Aug 2015 15:47:55 -0700
>
>> On Thu, Aug 27, 2015 at 3:42 PM, David Miller <davem@...emloft.net> wrote:
>>> If you fix it properly, by making every qdisc capable of being ->init()'d
>>> without explicit parameters, it will be the best behavior overall.
>>
>> The problem is ->init() is not even called when setting it as default,
>> since setting a default qdisc doesn't need to create a qdisc. This is
>> why the flag has to be in ops->flags rather than qdisc->flags.
>
> Just sounds like another shortcoming of how default qdiscs are handled,

It has to, due to its definition. I don't see any other way except we change
the meaning of the default qdisc.

> rather than a reason to not fix things properly.

If you mean the crash, my patch can fix it too by simply rejecting the
invalid and buggy case like HTB, even though I do have local patches
to fix it directly.

Like I said, the more important question is not if it crashes, it is if we
should reject invalid case as early as possible or just wait for an error
to happen later.
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