netdev - Re: [RGC PATCH v3.10] net: sched: validate that class is found in qdisc_tree_decrease

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Message-ID: <CALCkm3fPck6QKRRqOUxwB18WMG8wAqGyRR+bMKPtu8mn2apbww@mail.gmail.com>
Date:	Fri, 17 Jul 2015 17:27:01 -0700
From:	Alex Gartrell <alexgartrell@...il.com>
To:	Cong Wang <cwang@...pensource.com>
Cc:	Alex Gartrell <agartrell@...com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	kernel-team <kernel-team@...com>
Subject: Re: [RGC PATCH v3.10] net: sched: validate that class is found in qdisc_tree_decrease_qlen

On Fri, Jul 17, 2015 at 5:10 PM, Cong Wang <cwang@...pensource.com> wrote:
> Hmm, but in htb_delete() we do reset the leaf qdisc before removing the
> class from ha
>
>         if (!cl->level) {
>                 qlen = cl->un.leaf.q->q.qlen;
>                 qdisc_reset(cl->un.leaf.q);
>                 qdisc_tree_decrease_qlen(cl->un.leaf.q, qlen);
>         }
>
> therefore, the leaf fq_codel qdisc is supposed to have 0 skb after that,
> that is, the second fq_codel_reset() is supposed to return NULL immediately?
> Why is qdidsc_tree_decrease_qlen() called in the second fq_codel_reset()?
>
> Or there is a race condition between ->delete() and ->put()? In which new
> skb can be enqueued?

This makes the most sense to me, but I have ~32 hours of experience
with this subsystem :)

Taking that for granted, it seems like it'd be appropriate to note the
invariant in the code i've changed with a WARN_ON and to skip it, and
then to otherwise find a way to close the hole.  Do you agree?

-- 
Alex Gartrell <agartrell@...com>
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